Route GORM's logger through slog and bound it (closes #178 )

GORM's default logger printed the fully interpolated SQL to standard output on every statement that returned an error, including a plain record-not-found. On /webhook/{uuid} and on the login form the interpolated parameter is client-chosen and unbounded, so an unauthenticated client sized the operator's log, one line per request, at no level the operator could turn down. Every gorm.Open in the service now installs internal/gormlog, a gormlogger.Interface over the service's *slog.Logger. Its lines take the level the operator set and the handler internal/logger selected; a record-not-found is not logged as an error, since it is the expected outcome on both of those paths and each handler already records its own miss at DEBUG without the SQL; slow statements are kept at WARN above the same 200ms threshold GORM used; and every value it emits is spent through internal/logfield, the same encoded-byte budget the access log spends. MaxAccessLogLineBytes bounds a GORM line too, and internal/gormlog asserts each line against the constant directly. Trace orders its cases exactly as GORM's own Trace orders them -- error-that-is-not-a-miss, then slow, then routine -- so a statement that both missed and ran slow is still reported as slow. Ordering the drop first would have made this adapter strictly less observant than the IgnoreRecordNotFoundError option it was chosen over, on the two lookups the issue is about, and a miss is the statement most likely to be slow. The third gorm.Open, in the archive writer, was not named in the issue and had the same default. All three sites are pinned independently: internal/handlers covers the main and per-webhook databases, internal/delivery covers the archive writer, whose type is unexported. Reverting any one of the three to a bare &gorm.Config{} fails the suite. The flood test's per-line and volume assertions were vacuous, because the replaced default logger wrote only to a buffer while everything else went to the captured stdout. It now tees to stdout as GORM's real default does, so a reverted call site lands in the same capture and those assertions measure the whole writer set. internal/logfield gains the zero-headroom budget assertion and the rune-splitting case: a value built from one rune must keep exactly MaxBytes/EncodedBytes(r) of them, which a raw-byte budget fails and a LessOrEqual on the budget cannot catch. README: the ceiling now covers GORM, and the writers it does not cover are re-derived by measuring rather than by reading. fx's console logger and the Go runtime write to standard error. net/http's nil ErrorLog is not a separate writer at all -- slog.SetDefault redirects the log package's default logger into internal/logger's handler, so those lines arrive on standard output at INFO. A handler panic reaches that same path because chi's Recoverer crashes before writing, filed as #187, and is the widest line the service can write: measured at roughly 2,770 bytes against the stated 2,560, a width that moves with the goroutine number and the source paths in the stack, so only the fact that it exceeds the ceiling is stated as invariant.
Bound every slog line against client-chosen text (closes #176 )
2026-08-18 04:18:36 +00:00 · 2026-08-18 06:03:10 +02:00 · 2026-08-18 05:01:13 +02:00 · 2026-08-18 04:07:39 +02:00 · 2026-08-18 02:06:43 +00:00
20 changed files with 2042 additions and 361 deletions
--- a/README.md
+++ b/README.md
@@ -994,15 +994,16 @@ costs; log volume it caps rather than eliminates. A path that names no
 entrypoint is recorded by the handler at `DEBUG`, and the aggregate
 limiter logs its own rejections at `DEBUG` and without the path, so
 neither appears at all under the default level. The per-entrypoint
-limiter is the loud one: it still logs every rejection at `WARN` with
-the request path, which on this route is attacker-controlled text. A
-client hammering a single invented path is served `RECEIVER_RATE_LIMIT`
+limiter is the loud one: it logs every rejection at `WARN` with the
+request path, which on this route is attacker-controlled text. A client
+hammering a single invented path is served `RECEIVER_RATE_LIMIT`
 requests and has the rest of its aggregate budget rejected there, so
-the aggregate limit is what bounds those `WARN` lines — to under ten
-times `RECEIVER_RATE_LIMIT` per minute per client IP, 1080 at the
-defaults, where before it there was no bound at all. The access log is
-bounded by neither limit: every request is recorded once at `INFO`,
-served or rejected alike.
+the aggregate limit is what bounds the _number_ of those `WARN` lines —
+to under ten times `RECEIVER_RATE_LIMIT` per minute per client IP, 1080
+at the defaults, where before it there was no bound at all. Their
+_width_ is bounded by the field budgets below, the same ones the access
+log spends. The access log is bounded by neither limit: every request
+is recorded once at `INFO`, served or rejected alike.

 What the access log does bound is the _content_ of those lines. A 3xx
 or 4xx response logs the chi route pattern — `/webhook/{uuid}`,
@@ -1140,9 +1141,9 @@ the figure has headroom. `internal/middleware/accesslog_test.go`
 asserts it against 8 KB of client-chosen text in the path, in the
 query, and in each of `User-Agent`, `Referer` and `X-Request-Id`,
 including cases built from the characters the handlers escape, and
-against the widest line the service can be made to write: a 5xx that
-keeps its concrete path while all three header fields are also at their
-budget. Every case runs through both handlers `internal/logger` can
+against the widest access log line the service can be made to write: a
+5xx that keeps its concrete path while all three header fields are also
+at their budget. Every case runs through both handlers `internal/logger` can
 select — the JSON one and the text one it installs on a tty — since the
 two do not escape alike and the ceiling is quoted unqualified. Measured
 over a real connection, the widest line is 1,972 bytes.
@@ -1152,79 +1153,148 @@ that the rate is not bounded by the limits above on every route:
 `/.well-known/healthcheck` and `/s/*` sit behind no limiter, so there
 the multiplier is whatever the deployment will serve.

-That figure is now the ceiling on a second writer as well. GORM's own
-default logger printed the fully interpolated SQL — parameters and all
-— to standard output on every statement that returned an error,
-including a plain record-not-found, at a level no operator setting
-reached. Two of this service's lookups miss by design on
-unauthenticated routes: the entrypoint lookup behind `/webhook/{uuid}`
-and the user lookup behind the login form, whose path segment and
-submitted username the client picks outright. Every `gorm.Open` in the
-service now installs the adapter in `internal/gormlog` instead. It
-writes through the same `slog` logger as everything else, so its lines
-take the level the operator set and the handler `internal/logger`
-selected, and every value it emits is spent through the same 512-byte
-encoded budget (`internal/logfield`). A record-not-found is not logged
-as an error: it is the expected outcome on both of those paths, and
-each handler already records its own miss at `DEBUG`, without the SQL.
-Slow statements are kept — at `WARN`, above the same 200 ms threshold
-GORM used, with the statement bounded — because that report is the one
-thing GORM's logger gave an operator that nothing else here does, and
-a statement that both missed and ran slow is still reported as slow.
-The adapter orders those cases exactly as GORM's own `Trace` orders
-them, so dropping the miss costs an operator no report that GORM's
-`IgnoreRecordNotFoundError` would have kept. A
-GORM line spends at most two of those budgets, the statement and the
-driver error, against a smaller fixed portion than the access log's;
-`internal/gormlog/gormlog_test.go` asserts each line against
+**The same ceiling covers every other line the service writes through
+`slog` that carries text an unauthenticated client supplies.** The
+access log is not the only line a client can put its own text into, and
+a budget that held for one line and not the others would be worse than
+no stated budget at all. Every `slog` call an unauthenticated request
+can reach spends the same per-field budget through `internal/logfield`,
+and each carries strictly fewer client-supplied fields than the access
+log does, so none of them can be wider than it:
+
+| Log line                                   | Level   | Client-chosen value | Reachable unauthenticated                 |
+| ------------------------------------------ | ------- | ------------------- | ----------------------------------------- |
+| `request body exceeds limit` (413)         | `WARN`  | path, method        | yes — `MaxBodySize` precedes `RequireAuth` |
+| `csrf: token validation failed` (403)      | `WARN`  | path, method        | yes — `CSRF` precedes `RequireAuth`        |
+| `... rate limit exceeded` (429)            | `WARN`  | path                | yes, on the receiver                       |
+| `auth middleware: unauthenticated request` | `DEBUG` | path, method        | yes, by definition                         |
+| `entrypoint not found`                     | `DEBUG` | entrypoint UUID     | yes, on the receiver                       |
+| `user not found` / `invalid password`      | `DEBUG` | username            | yes, on the login form                     |
+| `login failure limit exceeded` (429)       | `WARN`  | path                | yes, on the login form                     |
+| `password verification capacity exhausted` | `WARN`  | path                | yes, on the login form                     |
+
+`DEBUG` being off by default is not a bound. An operator turning it on
+to diagnose a flood must not thereby hand the flood an unbounded write,
+so those lines are capped too.
+
+The last two rows are capped defensively rather than against a
+demonstrated width: chi routes `POST /pages/login` on a static pattern,
+so `r.URL.Path` there is the 12-byte constant `/pages/login` and each
+line lands near 120 bytes. `RecordLoginFailure` is nonetheless an
+exported method taking any `*http.Request`, and a future caller on a
+route with a URL parameter would widen the line. Since no request
+through the mux can, both caps are pinned by tests that call those two
+entry points directly with the path such a caller would supply.
+Removing either cap fails 14 subtests.
+
+`internal/middleware/logbound_test.go` and
+`internal/handlers/logbound_test.go` drive 8 KB of client-chosen text
+at each of these — 1 KB at `invalid password`, whose accounts are
+shared with the successful-login line, where a username past 4 KB
+overflows the session cookie and answers 500 before that line is
+written — through both handlers, and through seven fills: plain text
+as the baseline, and then the quotation mark, backslash, tab, newline,
+C0 control and astral non-printable, six characters the wider of the
+two handlers spends more on than the client spent sending them. Every
+case holds each line to the 2,560-byte ceiling. That per-line ceiling
+is what the figure above states, and every row establishes it.
+
+Three of the sites go further and bound the whole flood's output — the
+total bytes a run of distinct invented values wrote, which is the
+shape an operator sizing storage cares about. They are
+`request body exceeds limit`
+(`TestMaxBodySize_FloodOfOversizePathsDoesNotGrowTheLog`),
+`entrypoint not found` and `user not found` (the last two through
+`assertBoundedFlood`). The other rows carry no aggregate assertion;
+the per-line ceiling is what they establish.
+
+`internal/logfield/logfield_test.go` measures the per-rune charge
+against what the handlers really emit, over roughly 3,000 code points on
+each, so an undercharged rune fails a test rather than quietly
+falsifying the ceiling.
+
+**It covers GORM's statement logging as well.** GORM's own default
+logger printed the fully interpolated SQL — parameters and all — to
+standard output on every statement that returned an error, including a
+plain record-not-found, at a level no operator setting reached. Two of this service's lookups miss by design
+on unauthenticated routes: the entrypoint lookup behind
+`/webhook/{uuid}` and the user lookup behind the login form, whose path
+segment and submitted username the client picks outright. Every
+`gorm.Open` in the service now installs the adapter in
+`internal/gormlog` instead. It writes through the same `slog` logger as
+everything else, so its lines take the level the operator set and the
+handler `internal/logger` selected, and every value it emits is spent
+through the same `internal/logfield` budget. A record-not-found is not
+logged as an error: it is the expected outcome on both of those paths,
+and each handler already records its own miss at `DEBUG` — bounded, per
+the table above — without the SQL. Slow statements are kept, at `WARN`,
+above the same 200 ms threshold GORM used and with the statement
+bounded, because that report is the one thing GORM's logger gave an
+operator that nothing else here does. The adapter orders its cases
+exactly as GORM's own `Trace` orders them, so a statement that both
+missed and ran slow is still reported as slow, and dropping the miss
+costs an operator no report `IgnoreRecordNotFoundError` would have
+kept. A GORM line spends at most two of those budgets — the statement
+and the driver error — against a smaller fixed portion than the access
+log's, and `internal/gormlog/gormlog_test.go` asserts each line against
 `MaxAccessLogLineBytes` directly rather than leaving it as arithmetic.

-**What the ceiling does not cover.** It is a per-line bound on the
-access log and on GORM's statement logging, not a bound on every line
-this service writes. The exceptions are named here because a bound
-that is true of one writer and silently false of another is worse than
-no stated bound at all.
+What that ceiling does **not** cover, stated here so the figure is not
+read as more than it is:

- Other `slog` calls that reach a client-chosen value — the
-  `MaxBodySize` rejection, the CSRF failure, the receiver rate-limit
-  rejection, and the two lookup misses above — still log the request
-  path or the submitted username untruncated.
- The `log` delivery target (`internal/delivery/target_log.go`) writes
-  the entire inbound event, headers and body, to the log. That is what
-  the target is for. Each line is bounded per event by the 1 MB
-  receiver body cap, and it costs nothing unless an authenticated
-  operator creates a target of that type.
- Two writers that do not go through `internal/logger` at all, both on
-  standard error. `fx` prints the dependency graph and the lifecycle
+- **Lines carrying an authenticated operator's own input**, which are
+  not truncated at all. `webhook created` logs the submitted `name`
+  verbatim and `target URL blocked by SSRF protection` logs the target
+  host (both `internal/handlers/source_management.go`), as do the
+  `target_name` lines in `internal/delivery/engine.go` and
+  `internal/delivery/target_http.go`. The only bound on any of them is
+  the 1 MB form body cap, so a 100 KB `name` writes a single line of
+  roughly 600 KB — measured. This is deliberate: every one of these
+  requires an authenticated operator on a service with no
+  self-registration, and truncating the operator's own configuration
+  echoed back would cost debuggability against no adversary. It does
+  mean the 2,560-byte figure sizes unauthenticated traffic, not the
+  operator's own administrative requests.
+- The **`log` delivery target**, which writes the whole inbound event —
+  headers and body — to the log. This one is deliberate: capping it
+  would defeat the target, since emitting the payload is the delivery.
+  It costs nothing unless an authenticated operator creates a target of
+  that type on a specific webhook, and each line it writes is bounded
+  per event by the 1 MB receiver body cap. Adding one is a decision to
+  spend log volume on that webhook's payloads.
+- **Two writers that do not go through `internal/logger` at all**, both
+  on standard error. `fx` prints the dependency graph and the lifecycle
  hooks through its default console logger at startup and shutdown —
  nothing calls `fx.WithLogger`, and `fx.New` builds that logger over
-  `os.Stderr`. The Go runtime writes a panic or a fatal error itself;
-  a panic in a background worker rather than in a request handler is
-  the case that reaches it, since nothing recovers those. Neither
-  carries a client-chosen value at a client-chosen length: the five
-  `panic` calls in this service are invariant guards over constants
-  and over `crypto/rand`.
- `net/http`'s own faults, which are **not** a separate writer.
-  `internal/server/http.go` builds its server with a nil `ErrorLog`,
-  so `net/http` falls back to the `log` package's default logger — and
-  `internal/logger` calls `slog.SetDefault`, which redirects that
-  logger into whichever handler it installed. Those lines therefore
-  arrive on standard output, shaped like every other line, at `INFO`.
-  They are not truncated and they are not bounded by the ceiling: a
-  handler panic arrives as one record carrying a whole goroutine
-  stack, measured at 2,772 bytes against the ceiling's 2,560. The
-  value is the runtime's, not a client's.
- A handler panic reaches that path rather than the one it looks like
-  it should. `internal/server/routes.go` installs chi's
+  `os.Stderr`. The Go runtime writes a panic or a fatal error itself; a
+  panic in a background worker rather than in a request handler is the
+  case that reaches it, since nothing recovers those. Neither carries a
+  client-chosen value at a client-chosen length: the five `panic` calls
+  in this service are invariant guards over constants and over
+  `crypto/rand`.
+- **`net/http`'s own faults**, which are _not_ a separate writer.
+  `internal/server/http.go` builds its server with a nil `ErrorLog`, so
+  `net/http` falls back to the `log` package's default logger — and
+  `internal/logger` calls `slog.SetDefault`, which redirects that logger
+  into whichever handler it installed. Those lines therefore arrive on
+  standard output, shaped like every other line, at `INFO`. They are not
+  truncated and they are not bounded by the ceiling: a handler panic
+  arrives as one record carrying a whole goroutine stack, above the
+  ceiling's 2,560 bytes — measured at roughly 2,770 in one checkout. The
+  exact width is not an invariant, since it moves with the goroutine
+  number and with the source paths baked into the stack; that it exceeds
+  the ceiling does not move. The value is the runtime's, not a client's.
+- **A handler panic reaches that path** rather than the one it looks
+  like it should. `internal/server/routes.go` installs chi's
  `middleware.Recoverer` in front of every route, which is meant to
-  print the panic and its stack to standard error and answer 500. On
-  the Go version this service builds against it does neither: chi
-  v1.5.5's stack pretty-printer looks for a `panic(0x` frame that the
-  runtime no longer emits, walks past the end of its own slice, and
-  panics before writing a byte. That second panic escapes to
-  `net/http`, which drops the connection and reports it through the
-  nil `ErrorLog` above. Tracked separately in
-  https://git.eeqj.de/sneak/webhooker/issues/187.
+  print the panic and its stack to standard error and answer 500. On the
+  Go version this service builds against it does neither: chi v1.5.5's
+  stack pretty-printer looks for a `panic(0x` frame that the runtime no
+  longer emits, walks past the end of its own slice, and panics before
+  writing a byte. That second panic escapes to `net/http`, which drops
+  the connection and reports it through the nil `ErrorLog` above.
+  Tracked separately in
+  <https://git.eeqj.de/sneak/webhooker/issues/187>.

 Every limiter here — receiver, login, and password change — identifies
 the client the same way, through one shared key function: the
--- a/TODO.md
+++ b/TODO.md
@@ -24,8 +24,9 @@ event retention (#63), the database archiving target (#43), the admin
 password change flow (#65), policy compliance (#6), pinned lint tooling
 (#55), and fail-loud configuration parsing (#80).

-`next` holds the completed 1.0.0 milestone: every issue in it is closed,
-and it is verified green by cache-defeated container runs
+`next` holds the 1.0.0 milestone less its final four issues (#176, #178,
+#186, #187 — all in review or held on merge order), and is verified
+green by cache-defeated container runs
 (`docker build --no-cache-filter=lint --no-cache-filter=builder`). The
 CI status is not independently claimed here: a superseded run is
 recorded as `skipped` and still rolls up green, so a commit status on
@@ -39,15 +40,78 @@ of 2026-07-06.

 # Next Step

-Merge the milestone PR to `main` and tag 1.0.0 from it.
+Land the last four 1.0.0 issues, then merge the milestone PR to `main`
+and tag 1.0.0 from it. Merge order is forced by a real conflict on
+`README.md` and `internal/middleware/middleware.go`: #186, then #176,
+then #178, then #187.

-Two decisions are open and belong to the owner, neither blocking the
-tag: #115 (mask the `http` target's destination URL, implemented
-speculatively and awaiting a yes or no) and #125 (whether IPv6
-rate-limit keys should bucket by `/64`).
+Two items belong to the owner, neither blocking the tag. #150 was
+decided by the manager rather than left to stall the queue and is
+flagged on the issue for reversal if that call was wrong. #112 (whether
+`Completed Steps` should exist at all, given it once conflicted on every
+unit) is unanswered; the provisional ruling in force is that issue
+branches do not touch this file.

 # Completed Steps

+- 2026-08-18 Send the chi route pattern to Sentry rather than the
+  concrete path. The receiver's path carries the entrypoint capability
+  token, so every Sentry event from `/webhook/{uuid}` shipped a live
+  credential to a third party. Request `Data`, `QueryString`, `Cookies`
+  and `Env` are dropped and headers reduced to an allowlist (#179)
+- 2026-08-18 Read form fields from the POST body only. `r.FormValue`
+  merges the query string, so a login could be driven by URL parameters
+  — putting the password somewhere that lands in access logs, proxy
+  logs and browser history (#160)
+- 2026-08-18 Verify login credentials before spending rate-limit
+  budget, so a flood of wrong passwords cannot lock out the account it
+  is guessing at. The manager took this decision rather than stall the
+  queue; it is flagged on the issue for reversal (#150)
+- 2026-08-18 Run all linting in Docker via `Dockerfile.lint`. Host lint
+  was wrong in both directions from version skew and shared caches.
+  `script/lint` asserts the summary line, because `--no-cache-filter`
+  silently ignores a stage name it does not match — the flag that makes
+  the gate meaningful fails open (#109)
+- 2026-08-18 Serve an event's full stored body over HTTP. The list
+  query truncates for rendering, and that truncated value was the only
+  way to read a body, so the full payload was unreachable (#157)
+- 2026-08-18 Bound the access log line against client-chosen text.
+  `internal/logfield` budgets by *encoded* bytes, not runes, so a
+  handler's JSON escaping cannot multiply a field past its allowance
+  (#146)
+- 2026-08-18 Mark superseded CI commits `failure` rather than
+  `skipped`. A skipped run rolls up green, so a commit that was never
+  tested reported success (#152)
+- 2026-08-18 Set `fx.StopTimeout` inside the container stop grace, so
+  shutdown hooks are bounded by a deadline the orchestrator will
+  actually honour rather than being killed mid-flush (#134)
+- 2026-08-17 Bucket IPv6 rate-limit keys by `/64`. A single allocation
+  hands out 2^64 addresses, so per-address keying let one client mint
+  unlimited buckets. Manager decision, recorded on the issue (#125)
+- 2026-08-17 Correct release-blocking README and startup-warning
+  inaccuracies, including claims about behaviour the code does not have
+  (#151)
+- 2026-08-17 Fetch and verify Alpine.js at build time against
+  `static/vendor.sha256` instead of committing the minified blob, so
+  the dependency is pinned by hash rather than by trust (#145)
+- 2026-08-17 Bound the event log's rendered bodies in the query itself,
+  so a large stored payload cannot be read into memory just to be
+  truncated for display (#135)
+- 2026-08-17 Mask the `http` target's destination URL in the UI: it can
+  carry a bearer credential in its path or query, and was rendered
+  verbatim. Manager decision to mask unconditionally (#115)
+- 2026-08-14 Bound shutdown hooks by their stop context, so a hook that
+  hangs cannot hold the process past its grace period (#102)
+- 2026-08-14 Render templates via a buffer rather than the
+  `ResponseWriter`, so a template error part-way through cannot commit
+  a 200 and then fail — the response is written only once it is whole
+  (#123)
+- 2026-08-14 Align the session codec's max-age with the 7-day absolute
+  cap. The codec accepted cookies the session layer considered expired,
+  so the cap was enforced in one place and not the other (#108)
+- 2026-08-12 Warn when `TRUSTED_PROXIES` is empty in production, where
+  the safe default silently discards forwarded headers and every client
+  rate-limits as the proxy's address (#149)
 - 2026-08-12 Bound the receiver rate limit per client IP across the
  whole `/webhook/*` route. The existing limiter keyed on the request
  path and `/webhook/{uuid}` matches any single segment, so a client
--- a/internal/database/webhook_db_manager_test.go
+++ b/internal/database/webhook_db_manager_test.go
@@ -339,7 +339,12 @@ func TestWebhookDBManager_MultipleWebhooks(t *testing.T) {
 	var events []database.Event

 	require.NoError(t, db2.Find(&events).Error)
-	assert.Len(t, events, 1)
+
+	// require, not assert: this is exactly the regression the test
+	// guards, so the empty slice is the expected failure, and a
+	// non-fatal length check would index into it on the next line and
+	// panic the whole package test binary instead of failing here.
+	require.Len(t, events, 1)
 	assert.Equal(t, "PUT", events[0].Method)
 }

--- a/internal/delivery/target_log.go
+++ b/internal/delivery/target_log.go
@@ -11,6 +11,17 @@ import (
 // inbound webhook — the full request body and headers, plus
 // the method, content type, and the webhook and entrypoint
 // ids — then records a single successful attempt.
+//
+// This is the one log call in the service that deliberately writes
+// unbounded client-chosen bytes, so it is the one exception to the
+// per-field budgets in internal/logfield and to the ceiling stated on
+// middleware.MaxAccessLogLineBytes. Capping here would defeat the
+// target: emitting the payload IS the delivery. It costs nothing by
+// default — an authenticated operator has to create a target of this
+// type on a specific webhook before a single line is written — and the
+// bytes it writes are bounded per event by maxWebhookBodySize (1 MB).
+// An operator who adds one is choosing to spend log volume on the
+// payloads that webhook receives.
 type logTarget struct {
 	eng *Engine
 }
--- a/internal/gormlog/gormlog_test.go
+++ b/internal/gormlog/gormlog_test.go
@@ -334,13 +334,17 @@ func TestStatementError_LineIsBounded(t *testing.T) {
 func TestSucceedingStatement_LineIsBoundedOnEitherArm(t *testing.T) {
 	t.Parallel()

+	// "sql statement" is a substring of "slow sql statement", so the
+	// routine arm carries notWant as well: Contains alone cannot tell
+	// the two arms apart in that direction.
 	arms := []struct {
-		name string
-		slow time.Duration
-		want string
+		name    string
+		slow    time.Duration
+		want    string
+		notWant string
 	}{
-		{"slow", alwaysSlow, "slow sql statement"},
-		{"routine", neverSlow, "sql statement"},
+		{"slow", alwaysSlow, "slow sql statement", ""},
+		{"routine", neverSlow, "sql statement", "slow sql statement"},
 	}

 	for _, a := range arms {
@@ -362,6 +366,13 @@ func TestSucceedingStatement_LineIsBoundedOnEitherArm(t *testing.T) {
 					).Find(&got).Error)

 					assert.Contains(t, buf.String(), a.want)
+
+					if a.notWant != "" {
+						assert.NotContains(
+							t, buf.String(), a.notWant,
+						)
+					}
+
 					assertBounded(t, buf.String())
 				})
 			}
--- a/internal/handlers/auth.go
+++ b/internal/handlers/auth.go
@@ -5,6 +5,7 @@ import (
 	"strconv"

 	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/logfield"
 )

 // HandleLoginPage returns a handler for the login page (GET)
@@ -70,7 +71,9 @@ func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {

 		h.log.Info(
 			"user logged in",
-			"username", username,
+			"username", logfield.Truncate(
+				username, logfield.MaxBytes,
+			),
 			"user_id", user.ID,
 		)

@@ -117,7 +120,9 @@ func (h *Handlers) authenticateUser(
 	if !ok {
 		h.log.Warn(
 			"password verification capacity exhausted",
-			"path", r.URL.Path,
+			"path", logfield.Truncate(
+				r.URL.Path, logfield.MaxBytes,
+			),
 		)
 		h.renderLoginError(
 			w, r,
@@ -142,7 +147,17 @@ func (h *Handlers) authenticateUser(
 		h.dummyVerifications.Add(1)
 		database.VerifyDummyPassword(password)

-		h.log.Debug("user not found", "username", username)
+		// Login is unauthenticated, and the submitted username is
+		// a form field the client fills to any length the 1 MB
+		// body cap allows. On this branch it matched no row, so
+		// nothing else bounds it. The rate limiter caps how often
+		// the line is written, not how wide it is.
+		h.log.Debug(
+			"user not found",
+			"username", logfield.Truncate(
+				username, logfield.MaxBytes,
+			),
+		)
 		h.rejectLogin(w, r, username)

 		return user, err
@@ -160,7 +175,17 @@ func (h *Handlers) authenticateUser(
 	}

 	if !valid {
-		h.log.Debug("invalid password", "username", username)
+		// Reached only once the username matched a stored row, so
+		// it is bounded by the operator's own data. Capped anyway,
+		// so that every username this unauthenticated endpoint
+		// logs is capped and no reader has to work out which
+		// branch narrowed it.
+		h.log.Debug(
+			"invalid password",
+			"username", logfield.Truncate(
+				username, logfield.MaxBytes,
+			),
+		)
 		h.rejectLogin(w, r, username)

 		return user, errInvalidPassword
--- a/internal/handlers/export_test.go
+++ b/internal/handlers/export_test.go
@@ -2,11 +2,19 @@ package handlers

 import (
 	"html/template"
+	"log/slog"
 	"net/http"

 	"sneak.berlin/go/webhooker/internal/database"
 )

+// SetLogForTest replaces the handler's logger, so the handlers_test
+// package can assert on what a log line actually contains rather than
+// on what it is meant to contain.
+func (s *Handlers) SetLogForTest(log *slog.Logger) {
+	s.log = log
+}
+
 // MaxRenderedBodyBytesForTest exposes the event log's body cap
 // to the handlers_test package.
 const MaxRenderedBodyBytesForTest = maxRenderedBodyBytes
--- a/internal/handlers/gormlogbound_test.go
+++ b/internal/handlers/gormlogbound_test.go
@@ -7,7 +7,6 @@ import (
 	"log"
 	"net/http"
 	"net/http/httptest"
-	"net/url"
 	"os"
 	"strconv"
 	"strings"
@@ -244,7 +243,7 @@ func floodUnauthenticated(

 		for range reps {
 			postWebhook(t, h, value)
-			postLogin(t, h, value)
+			postUnknownLogin(t, h, value)

 			requests += 2
 		}
@@ -324,29 +323,15 @@ func postWebhook(
 	require.Equal(t, http.StatusNotFound, w.Code)
 }

-// postLogin submits the login form with an unknown username. The
-// field is bounded only by the 1 MB body cap, and the lookup behind
-// it misses by design.
-func postLogin(
+// postUnknownLogin submits the login form with an unknown username,
+// through the postLogin helper in logbound_test.go. The field is
+// bounded only by the 1 MB body cap, and the lookup behind it misses
+// by design.
+func postUnknownLogin(
 	t *testing.T, h *handlers.Handlers, username string,
 ) {
 	t.Helper()

-	form := url.Values{}
-	form.Set("username", username)
-	form.Set("password", "not-the-password")
-
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodPost, "/pages/login",
-		strings.NewReader(form.Encode()),
-	)
-	req.Header.Set(
-		"Content-Type", "application/x-www-form-urlencoded",
-	)
-
-	w := httptest.NewRecorder()
-	h.HandleLoginSubmit().ServeHTTP(w, req)
-
 	// 401 while the client still has failure budget against this
 	// username, 429 once the login guard has taken it away. Both
 	// outcomes sit behind the user lookup, which is the query this
@@ -354,7 +339,7 @@ func postLogin(
 	require.Contains(
 		t,
 		[]int{http.StatusUnauthorized, http.StatusTooManyRequests},
-		w.Code,
+		postLogin(t, h, username),
 	)
 }

@@ -405,11 +390,11 @@ func assertFloodBounded(t *testing.T, label, out string) {
 //     the adapter drops the record-not-found, so the capture holds
 //     nothing but fixed-string warnings.
 //
-// The level is left where newTestApp leaves it, at INFO, deliberately.
-// At DEBUG the handlers' own miss lines log the client-chosen
-// entrypoint and username untruncated — the first carve-out in the
-// README's ceiling section, and https://git.eeqj.de/sneak/webhooker/issues/176's
-// to fix, not this one's.
+// The level is left where newTestApp leaves it, at INFO: the level an
+// operator runs at by default, and the one the defect was visible at.
+// The handlers' own miss lines sit at DEBUG and spend the same
+// logfield budget as everything else, so they are not what makes
+// either assertion above bite at any level.
 //
 // It is deliberately not parallel: it redirects os.Stdout and replaces
 // gormlogger.Default, both of which are process-global. Go runs every
--- a/internal/handlers/logbound_test.go
+++ b/internal/handlers/logbound_test.go
@@ -0,0 +1,543 @@
+package handlers_test
+
+// The handler-side half of the log-field audit. Two slog calls in
+// this package reach a value an UNAUTHENTICATED client picks outright
+// and of a length it picks outright:
+//
+//   - the unknown-entrypoint DEBUG line on /webhook/{uuid}, whose
+//     path segment matched no stored entrypoint and so is bounded by
+//     nothing;
+//   - the failed-login DEBUG lines, whose username is a form field.
+//
+// Both are at DEBUG, which is off in production by default. That is
+// not a bound: an operator turning DEBUG on to diagnose a flood must
+// not thereby hand the flood an unbounded write. Both spend the same
+// internal/logfield budget as the access log, and both are held here
+// to middleware.MaxAccessLogLineBytes.
+//
+// The two login lines past the username lookup — "invalid password"
+// and "user logged in" — carry the same cap without needing it, since
+// by then the value is a stored row rather than the client's. They are
+// pinned here too, so the caps cannot be dropped silently.
+//
+// So is the "password verification capacity exhausted" WARN line,
+// whose path chi pins to the constant "/pages/login" on the one route
+// that reaches it. Its cap is defensive, and the test below drives the
+// handler directly with the path a parameterised route would give it,
+// because an unasserted cap is one a later edit removes for free.
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	"github.com/go-chi/chi"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/handlers"
+	"sneak.berlin/go/webhooker/internal/middleware"
+)
+
+// floodRequests is the number of distinct invented values each flood
+// drives through the call site under test.
+const floodRequests = 32
+
+// oversizedFillBytes is the length of the single client-chosen value
+// used to show that line size does not track input size.
+const oversizedFillBytes = 8192
+
+// attackerMarker and tailMarker sit at the END of every oversized
+// value, past every budget. Their absence from the log is what
+// proves the value was cut rather than merely being short.
+const (
+	attackerMarker = "QQATTACKERTEXTQQ"
+	tailMarker     = "QQTRUNCATEDTAILQQ"
+)
+
+// escapeFills are the characters the log handlers escape, so a value
+// built out of them costs more on the line than it did on the wire. A
+// budget counted in raw bytes passes the plain case and fails these.
+//
+// U+1000C is unassigned, hence non-printable, and strconv.Quote
+// spells it as a ten-byte \UXXXXXXXX while the JSON handler passes
+// its four UTF-8 bytes through; only the text shape of these tests
+// reaches that charge.
+func escapeFills() map[string]string {
+	return map[string]string{
+		"plain":     "x",
+		"quote":     `"`,
+		"backslash": `\`,
+		"tab":       "\t",
+		"newline":   "\n",
+		// A C0 control neither handler has a short escape for, so
+		// each one costs six bytes on the line against the single
+		// byte it cost to send: the widest multiplier a client can
+		// drive, and the case a raw-byte budget breaks on first.
+		//
+		// This fill is load-bearing, not decoration. Budgeting raw
+		// bytes instead of encoded is caught by this fill alone,
+		// and only under the JSON handler, at 3,072 bytes against
+		// the 2,560 ceiling. Drop it and that mutation passes.
+		"control": "\x01",
+		"astral":  "\U0001000C",
+	}
+}
+
+// logHandlers are the two handlers internal/logger can install.
+func logHandlers() map[string]func(
+	io.Writer, *slog.HandlerOptions,
+) slog.Handler {
+	return map[string]func(
+		io.Writer, *slog.HandlerOptions,
+	) slog.Handler{
+		"json": func(
+			w io.Writer, o *slog.HandlerOptions,
+		) slog.Handler {
+			return slog.NewJSONHandler(w, o)
+		},
+		"text": func(
+			w io.Writer, o *slog.HandlerOptions,
+		) slog.Handler {
+			return slog.NewTextHandler(w, o)
+		},
+	}
+}
+
+// oversizedFill builds an 8 KB client-chosen value out of
+// repetitions of ch, with both markers at its far end.
+func oversizedFill(ch string) string {
+	return "x" + strings.Repeat(ch, oversizedFillBytes) +
+		attackerMarker + tailMarker
+}
+
+// capturingHandlers builds a Handlers whose log is captured into the
+// returned buffer at DEBUG through the named handler.
+//
+// extra is passed to fx.Populate alongside the Handlers, for the call
+// sites that also need the database the client's value is looked up
+// in, or the Middleware whose resource has to be exhausted before the
+// branch under test is reached.
+func capturingHandlers(
+	t *testing.T,
+	newHandler func(io.Writer, *slog.HandlerOptions) slog.Handler,
+	extra ...any,
+) (*handlers.Handlers, *bytes.Buffer) {
+	t.Helper()
+
+	var h *handlers.Handlers
+
+	app := newTestApp(t, append([]any{&h}, extra...)...)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	buf := new(bytes.Buffer)
+	h.SetLogForTest(slog.New(newHandler(
+		buf, &slog.HandlerOptions{Level: slog.LevelDebug},
+	)))
+
+	return h, buf
+}
+
+// logLines splits the captured buffer into non-empty lines, holding
+// each to the stated per-line ceiling.
+func logLines(t *testing.T, buf *bytes.Buffer) []string {
+	t.Helper()
+
+	var lines []string
+
+	for line := range strings.SplitSeq(
+		strings.TrimSpace(buf.String()), "\n",
+	) {
+		if line == "" {
+			continue
+		}
+
+		require.LessOrEqual(
+			t, len(line), middleware.MaxAccessLogLineBytes,
+			"log line exceeded its bound: %s", line,
+		)
+
+		lines = append(lines, line)
+	}
+
+	return lines
+}
+
+// assertNoClientText fails if the far end of the client-chosen input
+// survived into the log.
+func assertNoClientText(t *testing.T, buf *bytes.Buffer) {
+	t.Helper()
+
+	assert.NotContains(
+		t, buf.String(), attackerMarker,
+		"log carried attacker-chosen text",
+	)
+	assert.NotContains(
+		t, buf.String(), tailMarker,
+		"log carried the tail of the attacker-chosen text",
+	)
+}
+
+// receiverRouter mounts the real receiver handler at the production
+// route pattern.
+func receiverRouter(h *handlers.Handlers) *chi.Mux {
+	router := chi.NewRouter()
+	router.Post("/webhook/{uuid}", h.HandleWebhook())
+
+	return router
+}
+
+// postReceiver sends one POST at /webhook/<segment>.
+//
+// RawPath is cleared after parsing so chi routes on the decoded path
+// and the handler sees the raw bytes rather than their percent-escaped
+// spelling. That is the harder case for the budget: the escaped
+// spelling is plain ASCII, which costs one byte per byte, while the
+// decoded bytes are what the log handler has to escape.
+func postReceiver(
+	t *testing.T, router *chi.Mux, segment string,
+) int {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(
+		context.Background(),
+		http.MethodPost,
+		"/webhook/"+url.PathEscape(segment),
+		strings.NewReader(""),
+	)
+	req.URL.RawPath = ""
+
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	return w.Code
+}
+
+// postLogin submits the login form with the given username and a
+// non-empty password.
+func postLogin(
+	t *testing.T, h *handlers.Handlers, username string,
+) int {
+	t.Helper()
+
+	return postLoginWithPassword(t, h, username, "not-the-password")
+}
+
+// postLoginWithPassword submits the login form with both credentials
+// chosen by the caller, so a test can reach the branches past the
+// username lookup.
+func postLoginWithPassword(
+	t *testing.T, h *handlers.Handlers, username, password string,
+) int {
+	t.Helper()
+
+	form := url.Values{
+		"username": {username},
+		"password": {password},
+	}
+
+	req := httptest.NewRequestWithContext(
+		context.Background(),
+		http.MethodPost,
+		"/pages/login",
+		strings.NewReader(form.Encode()),
+	)
+	req.Header.Set(
+		"Content-Type", "application/x-www-form-urlencoded",
+	)
+
+	w := httptest.NewRecorder()
+	h.HandleLoginSubmit().ServeHTTP(w, req)
+
+	return w.Code
+}
+
+// TestUnknownEntrypoint_LogLineDoesNotTrackPathSize drives 8 KB of
+// client-chosen path at the unauthenticated receiver's
+// unknown-entrypoint DEBUG line and holds it to the same ceiling the
+// access log states.
+func TestUnknownEntrypoint_LogLineDoesNotTrackPathSize(t *testing.T) {
+	t.Parallel()
+
+	for handlerName, newHandler := range logHandlers() {
+		for fillName, fill := range escapeFills() {
+			t.Run(handlerName+"/"+fillName, func(t *testing.T) {
+				t.Parallel()
+
+				h, buf := capturingHandlers(t, newHandler)
+				router := receiverRouter(h)
+
+				for i := range floodRequests {
+					assert.Equal(
+						t,
+						http.StatusNotFound,
+						postReceiver(
+							t, router,
+							oversizedFill(fill)+
+								strings.Repeat("y", i),
+						),
+					)
+				}
+
+				lines := logLines(t, buf)
+				require.Len(t, lines, floodRequests)
+				assertNoClientText(t, buf)
+
+				assertBoundedFlood(t, buf.Len())
+			})
+		}
+	}
+}
+
+// TestFailedLogin_LogLineDoesNotTrackUsernameSize drives 8 KB of
+// client-chosen username at the unauthenticated login endpoint's
+// DEBUG line and holds it to the same ceiling.
+func TestFailedLogin_LogLineDoesNotTrackUsernameSize(t *testing.T) {
+	t.Parallel()
+
+	for handlerName, newHandler := range logHandlers() {
+		for fillName, fill := range escapeFills() {
+			t.Run(handlerName+"/"+fillName, func(t *testing.T) {
+				t.Parallel()
+
+				h, buf := capturingHandlers(t, newHandler)
+
+				for i := range floodRequests {
+					assert.Equal(
+						t,
+						http.StatusUnauthorized,
+						postLogin(
+							t, h,
+							oversizedFill(fill)+
+								strings.Repeat("y", i),
+						),
+					)
+				}
+
+				lines := logLines(t, buf)
+				require.Len(t, lines, floodRequests)
+				assertNoClientText(t, buf)
+
+				assertBoundedFlood(t, buf.Len())
+			})
+		}
+	}
+}
+
+// storedUserPassword is the password held by the oversize accounts
+// the test below creates.
+const storedUserPassword = "correct-horse-battery-staple"
+
+// storedFillBytes is the raw length of the client-chosen value in
+// those accounts' usernames. It is well past the 512-byte field
+// budget, so the line is still truncated, but short enough that the
+// session cookie a successful login writes stays inside
+// securecookie's 4 KB limit: the cookie is written BEFORE the
+// "user logged in" line, so an 8 KB username answers 500 and never
+// reaches it.
+const storedFillBytes = 1024
+
+// storedFill builds a username fill of storedFillBytes raw bytes out
+// of repetitions of ch, with both markers at its far end.
+func storedFill(ch string) string {
+	return "x" + strings.Repeat(ch, storedFillBytes/len(ch)) +
+		attackerMarker + tailMarker
+}
+
+// TestStoredUsername_LogLinesDoNotTrackUsernameSize pins the two
+// login lines that are reached only AFTER the username matched a
+// stored row: "invalid password" and "user logged in". Neither
+// strictly needs its cap — the value is the operator's own data by
+// then, not the client's — but both carry one so that every username
+// this unauthenticated endpoint logs is capped, and an unasserted cap
+// is one a later edit removes for free.
+//
+// One app per handler with the accounts created inside it, and no
+// parallelism below that level: every account costs an Argon2id hash
+// and every attempt costs a verification.
+func TestStoredUsername_LogLinesDoNotTrackUsernameSize(t *testing.T) {
+	t.Parallel()
+
+	for handlerName, newHandler := range logHandlers() {
+		t.Run(handlerName, func(t *testing.T) {
+			t.Parallel()
+
+			var db *database.Database
+
+			h, buf := capturingHandlers(t, newHandler, &db)
+
+			hash, err := database.HashPassword(storedUserPassword)
+			require.NoError(t, err)
+
+			fills := escapeFills()
+			for fillName, fill := range fills {
+				username := storedFill(fill) + fillName
+
+				require.NoError(t, db.DB().Create(&database.User{
+					Username: username,
+					Password: hash,
+				}).Error)
+
+				// Matched the row, wrong secret: "invalid
+				// password".
+				assert.Equal(
+					t, http.StatusUnauthorized,
+					postLoginWithPassword(
+						t, h, username, "not-the-password",
+					),
+				)
+
+				// Matched the row, right secret: "user logged
+				// in".
+				assert.Equal(
+					t, http.StatusSeeOther,
+					postLoginWithPassword(
+						t, h, username, storedUserPassword,
+					),
+				)
+			}
+
+			lines := logLines(t, buf)
+			require.Len(t, lines, 2*len(fills))
+			assertNoClientText(t, buf)
+		})
+	}
+}
+
+// maxVerificationSlots bounds how many slots the loop below will
+// take before it gives up, so a semaphore that never fills fails the
+// test instead of hanging it. It is deliberately larger than the
+// real concurrency bound, which is not exported to this package.
+const maxVerificationSlots = 64
+
+// canceledContext returns a context that is already done. A
+// verification request carrying one takes the ctx.Done() branch of
+// the semaphore's bounded wait immediately, so these cases turn on
+// the semaphore being full rather than on a five-second timer firing.
+// Nothing here is timing-dependent.
+func canceledContext() context.Context {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	return ctx
+}
+
+// holdEveryVerificationSlot takes verification slots until one is
+// refused, and releases them when the test ends. A free slot is
+// handed out before any context is consulted, so a canceled context
+// cannot make this loop stop early: it stops exactly when the slots
+// are gone.
+func holdEveryVerificationSlot(
+	t *testing.T, mw *middleware.Middleware,
+) {
+	t.Helper()
+
+	for range maxVerificationSlots {
+		release, ok := mw.BeginPasswordVerification(canceledContext())
+		if !ok {
+			return
+		}
+
+		t.Cleanup(release)
+	}
+
+	require.Fail(t, "the verification semaphore never filled")
+}
+
+// postLoginAtPath submits the login form at a path of the caller's
+// choosing, with a canceled context.
+func postLoginAtPath(
+	t *testing.T, h *handlers.Handlers, path string,
+) int {
+	t.Helper()
+
+	form := url.Values{
+		"username": {"someone"},
+		"password": {"not-the-password"},
+	}
+
+	req := httptest.NewRequestWithContext(
+		canceledContext(),
+		http.MethodPost,
+		path,
+		strings.NewReader(form.Encode()),
+	)
+	req.Header.Set(
+		"Content-Type", "application/x-www-form-urlencoded",
+	)
+
+	w := httptest.NewRecorder()
+	h.HandleLoginSubmit().ServeHTTP(w, req)
+
+	return w.Code
+}
+
+// TestVerificationCapacity_LogLineDoesNotTrackPathSize pins the cap
+// on the "password verification capacity exhausted" WARN line.
+//
+// The one route that reaches it is chi's static "/pages/login", so no
+// request through the mux can widen the line; the handler is driven
+// directly here with the path a parameterised route would give it,
+// which is what that cap exists for. Without this test, removing the
+// logfield.Truncate there fails nothing.
+func TestVerificationCapacity_LogLineDoesNotTrackPathSize(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	for handlerName, newHandler := range logHandlers() {
+		for fillName, fill := range escapeFills() {
+			t.Run(handlerName+"/"+fillName, func(t *testing.T) {
+				t.Parallel()
+
+				var mw *middleware.Middleware
+
+				h, buf := capturingHandlers(t, newHandler, &mw)
+
+				holdEveryVerificationSlot(t, mw)
+
+				assert.Equal(
+					t,
+					http.StatusServiceUnavailable,
+					postLoginAtPath(
+						t, h,
+						"/source/"+url.PathEscape(
+							oversizedFill(fill),
+						)+"/login",
+					),
+				)
+
+				lines := logLines(t, buf)
+				require.Len(t, lines, 1)
+				assertNoClientText(t, buf)
+			})
+		}
+	}
+}
+
+// assertBoundedFlood holds the whole flood's log output to what the
+// stated per-line ceiling allows. The flood sent
+// floodRequests * oversizedFillBytes bytes of client-chosen text;
+// this is the assertion that the log did not grow with it.
+func assertBoundedFlood(t *testing.T, got int) {
+	t.Helper()
+
+	sent := floodRequests * oversizedFillBytes
+
+	require.Less(
+		t, got, sent/2,
+		"log volume tracked the size of the flood's input",
+	)
+	require.LessOrEqual(
+		t, got,
+		floodRequests*middleware.MaxAccessLogLineBytes,
+	)
+}
--- a/internal/handlers/webhook.go
+++ b/internal/handlers/webhook.go
@@ -9,6 +9,7 @@ import (
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
+	"sneak.berlin/go/webhooker/internal/logfield"
 )

 const (
@@ -125,9 +126,16 @@ func (h *Handlers) lookupEntrypoint(
 		"path = ?", entrypointUUID,
 	).First(&entrypoint)
 	if result.Error != nil {
+		// The receiver is unauthenticated and /webhook/{uuid}
+		// matches any single segment, so this value is entirely
+		// client-chosen on exactly the branch where the lookup
+		// failed. DEBUG is off by default; the cap is what keeps
+		// turning it on from restoring an unbounded write.
 		h.log.Debug(
 			"entrypoint not found",
-			"path", entrypointUUID,
+			"path", logfield.Truncate(
+				entrypointUUID, logfield.MaxBytes,
+			),
 		)
 		http.NotFound(w, r)

--- a/internal/logfield/logfield.go
+++ b/internal/logfield/logfield.go
@@ -1,11 +1,14 @@
-// Package logfield bounds a client-supplied value against what the log
-// handler will actually emit for it, so a line's size is set by this
-// service rather than by the client that provoked it.
+// Package logfield bounds the client-supplied values this service
+// writes into its logs.
 //
-// It lives outside internal/middleware because more than one writer
-// needs it: the access log, and the GORM adapter in internal/gormlog,
-// which logs SQL with the client-chosen parameters interpolated into
-// it. One budget, one implementation.
+// Any log field whose content a client picks is spent against a budget
+// here, in ENCODED bytes rather than in the bytes the client sent, so
+// that escaping cannot multiply a field past its nominal size. One
+// budget and one implementation serves the access log in
+// internal/middleware and every other slog call that reaches a
+// client-chosen path, header or form value; a second, ad-hoc
+// truncation somewhere else in the tree is the thing this package
+// exists to prevent.
 package logfield

 import (
@@ -15,19 +18,20 @@ import (
 )

 const (
-	// MaxBytes is the default budget for a field whose value the
-	// client supplies outright. It is spent in ENCODED bytes (see
-	// Truncate), so 512 still holds a real browser's User-Agent whole
-	// — those are plain ASCII, which encodes one byte for one — while
-	// a value built from characters the encoder escapes keeps a
-	// shorter prefix. That is the intended trade: 500 quotation marks
-	// are not a debugging asset.
+	// MaxBytes is the default budget for a log field whose value the
+	// client supplies outright: a URL, a path, a header, a form value.
+	// The budget is spent in ENCODED bytes (see Truncate), so 512 still
+	// holds a real browser's User-Agent whole — those are plain ASCII,
+	// which encodes one byte for one — while a value built from
+	// characters the encoder escapes keeps a shorter prefix. That is
+	// the intended trade: 500 quotation marks are not a debugging
+	// asset.
 	MaxBytes = 512

-	// truncationMarker is appended to any value Truncate cut, so a
-	// short value and a truncated one cannot be confused. It is
-	// charged on top of the budget, not inside it.
-	truncationMarker = "[truncated]"
+	// TruncationMarker is appended to any field that was cut, so a
+	// short value and a truncated one cannot be confused. It is charged
+	// on top of the budget, not inside it.
+	TruncationMarker = "[truncated]"
 )

 // EncodedBytes is what r costs on the line once the log handler has
@@ -45,9 +49,9 @@ const (
 // 955,086 unassigned, private-use and format code points on planes 1
 // to 16.
 //
-// Charging ten there is what makes the stated per-line ceiling hold
-// for the tty handler as well: U+1000C encodes as F0 90 80 8C, every
-// byte >= 0x80, which httpguts.ValidHeaderFieldValue accepts and
+// Charging ten there is what makes the stated line ceilings hold for
+// the tty handler as well: U+1000C encodes as F0 90 80 8C, every byte
+// >= 0x80, which httpguts.ValidHeaderFieldValue accepts and
 // net/textproto does not strip, so a header can be filled with them.
 //
 // Both handlers pass printable runes through as their own UTF-8, so
@@ -85,20 +89,19 @@ func EncodedBytes(r rune) int {
 // grows a value, so a raw budget spent on characters the encoder
 // escapes buys a field several times its nominal size — and the line
 // is the thing an operator is told to multiply by their request rate.
-// Charging each rune what it will actually cost is what makes the
-// stated ceiling true rather than merely larger. The visible
-// consequence is that an escape-heavy value keeps a shorter prefix
-// than a plain one, which is the correct trade.
+// Charging each rune what it will actually cost is what makes a stated
+// ceiling true rather than merely larger. The visible consequence is
+// that an escape-heavy value keeps a shorter prefix than a plain one,
+// which is the correct trade.
 //
 // The result is always valid UTF-8. A cut on a byte boundary can split
-// a multi-byte rune, and a header — or a SQL literal — can carry bytes
-// that were never valid UTF-8 to begin with; both are dropped rather
-// than kept, since an encoder would otherwise spend six bytes
-// replacing each one.
+// a multi-byte rune, and a header can carry bytes that were never
+// valid UTF-8 to begin with; both are dropped rather than kept, since
+// an encoder would otherwise spend six bytes replacing each one.
 func Truncate(s string, maxBytes int) string {
 	// No rune encodes to fewer bytes than it occupies, so nothing past
 	// maxBytes raw can fit the budget. Slicing first bounds the scan
-	// below to the budget rather than to the size of the value the
+	// below to the budget rather than to the size of the header the
 	// client sent.
 	window, cut := s, false
 	if len(window) > maxBytes {
@@ -136,5 +139,5 @@ func Truncate(s string, maxBytes int) string {
 		return kept.String()
 	}

-	return kept.String() + truncationMarker
+	return kept.String() + TruncationMarker
 }
--- a/internal/logfield/logfield_test.go
+++ b/internal/logfield/logfield_test.go
@@ -2,6 +2,7 @@ package logfield_test

 import (
 	"bytes"
+	"io"
 	"log/slog"
 	"strings"
 	"testing"
@@ -12,6 +13,213 @@ import (
 	"sneak.berlin/go/webhooker/internal/logfield"
 )

+// budget is the field budget these tests spend. Small enough that a
+// cut is unambiguous, large enough to hold several runes of every
+// width.
+const budget = 64
+
+// sampleRunes is how many runes wide the values in the charge test
+// are. The handlers add a constant per field — a pair of quotes when
+// the value needs quoting — so the per-rune charge is only visible
+// once it is amortised over a run of them.
+const sampleRunes = 64
+
+// quotingSlack is that constant: the pair of quotes a handler adds to
+// a value that needs them and omits from one that does not.
+const quotingSlack = 2
+
+// newHandlers are the two handlers internal/logger can install. Time
+// is dropped so a line's width is a function of its value alone —
+// RFC3339Nano trims trailing zeros, so two consecutive timestamps do
+// not render to the same number of bytes.
+func newHandlers() map[string]func(io.Writer) slog.Handler {
+	opts := &slog.HandlerOptions{
+		Level: slog.LevelDebug,
+		ReplaceAttr: func(_ []string, a slog.Attr) slog.Attr {
+			if a.Key == slog.TimeKey {
+				return slog.Attr{}
+			}
+
+			return a
+		},
+	}
+
+	return map[string]func(io.Writer) slog.Handler{
+		"json": func(w io.Writer) slog.Handler {
+			return slog.NewJSONHandler(w, opts)
+		},
+		"text": func(w io.Writer) slog.Handler {
+			return slog.NewTextHandler(w, opts)
+		},
+	}
+}
+
+// renderedWidth is the number of bytes a handler writes for a line
+// carrying value in a single attribute.
+func renderedWidth(
+	newHandler func(io.Writer) slog.Handler,
+	value string,
+) int {
+	buf := new(bytes.Buffer)
+	slog.New(newHandler(buf)).Info("m", "v", value)
+
+	return buf.Len()
+}
+
+// chargeTestRunes is the set of code points the charge test measures:
+// every rune in the first two planes' worth of the BMP that the
+// handlers are most likely to treat specially, the separators that
+// only slog's JSON handler escapes, and a stratified sample across
+// the rest of Unicode so the astral charge is exercised on more than
+// one hand-picked rune.
+func chargeTestRunes() []rune {
+	const (
+		denseCeiling = 0x800
+		stride       = 1021
+		surrogateLo  = 0xD800
+		surrogateHi  = 0xDFFF
+	)
+
+	var runes []rune
+
+	keep := func(r rune) {
+		if r >= surrogateLo && r <= surrogateHi {
+			return
+		}
+
+		runes = append(runes, r)
+	}
+
+	for r := range rune(denseCeiling) {
+		keep(r)
+	}
+
+	for _, r := range []rune{
+		0x2028, 0x2029, 0x200B, 0x4E00, 0xE000, 0xFFFD,
+		0x1000C, 0x1F600, 0xE0001, 0x10FFFF,
+	} {
+		keep(r)
+	}
+
+	for r := rune(denseCeiling); r <= utf8.MaxRune; r += stride {
+		keep(r)
+	}
+
+	return runes
+}
+
+// TestEncodedBytes_ChargesAtLeastWhatTheHandlersEmit is the property
+// the whole capping scheme rests on: a rune may not cost more on the
+// line than the budget was charged for it. An undercharged rune is
+// how a stated ceiling becomes false without any test noticing, so
+// the charge is measured against what the handlers actually write
+// rather than against the escaping rules as read.
+func TestEncodedBytes_ChargesAtLeastWhatTheHandlersEmit(t *testing.T) {
+	t.Parallel()
+
+	for name, newHandler := range newHandlers() {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			// 'a' is a printable ASCII rune, charged exactly one
+			// byte, so it is the zero point the other runes are
+			// measured against.
+			base := renderedWidth(
+				newHandler, strings.Repeat("a", sampleRunes),
+			)
+
+			for _, r := range chargeTestRunes() {
+				got := renderedWidth(
+					newHandler,
+					strings.Repeat(string(r), sampleRunes),
+				)
+				charged := sampleRunes *
+					(logfield.EncodedBytes(r) - 1)
+
+				require.LessOrEqual(
+					t, got-base, charged+quotingSlack,
+					"U+%04X costs more on the line than "+
+						"EncodedBytes charges for it",
+					r,
+				)
+			}
+		})
+	}
+}
+
+// TestTruncate_SpendsNoMoreThanTheBudget holds the result to the
+// budget in ENCODED bytes, which is the unit the budget is stated in.
+// A raw-byte cap passes the ASCII case here and fails every other
+// one.
+func TestTruncate_SpendsNoMoreThanTheBudget(t *testing.T) {
+	t.Parallel()
+
+	for name, fill := range map[string]string{
+		"plain":     "x",
+		"quote":     `"`,
+		"backslash": `\`,
+		"tab":       "\t",
+		"newline":   "\n",
+		"control":   "\x01",
+		"astral":    "\U0001000C",
+		// U+4E00, a printable multi-byte rune, charged its three
+		// UTF-8 bytes rather than an escape. Spelled numerically
+		// because gosmopolitan rejects Han in a string literal.
+		"cjk": string(rune(0x4E00)),
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			got := logfield.Truncate(
+				strings.Repeat(fill, budget*8), budget,
+			)
+
+			require.True(
+				t, strings.HasSuffix(
+					got, logfield.TruncationMarker,
+				),
+				"an oversized value must be marked as cut",
+			)
+
+			spent := 0
+			for _, r := range strings.TrimSuffix(
+				got, logfield.TruncationMarker,
+			) {
+				spent += logfield.EncodedBytes(r)
+			}
+
+			assert.LessOrEqual(t, spent, budget)
+			assert.True(t, utf8.ValidString(got))
+		})
+	}
+}
+
+// TestTruncate_LeavesShortValuesAlone keeps the marker meaningful: a
+// value that fits comes back byte for byte, so a marked value is
+// always a cut one.
+func TestTruncate_LeavesShortValuesAlone(t *testing.T) {
+	t.Parallel()
+
+	for _, s := range []string{
+		"", "GET", "/source/abc/edit", "Mozilla/5.0 (X11)",
+	} {
+		assert.Equal(t, s, logfield.Truncate(s, budget))
+	}
+}
+
+// TestTruncate_DropsInvalidUTF8 covers the bytes a header can carry
+// that were never valid UTF-8. Keeping them would make the encoder
+// spend six bytes apiece replacing them, which is exactly the
+// amplification the budget exists to prevent.
+func TestTruncate_DropsInvalidUTF8(t *testing.T) {
+	t.Parallel()
+
+	got := logfield.Truncate("a\xffb\xfe\xfec", budget)
+
+	assert.Equal(t, "abc", got)
+	assert.True(t, utf8.ValidString(got))
+}
+
 // encodedCost is what a whole string costs on a line, by the same
 // accounting Truncate spends its budget with.
 func encodedCost(s string) int {
@@ -24,29 +232,35 @@ func encodedCost(s string) int {
 }

 // TestTruncate_SpendsEncodedBytesNotRawBytes is the zero-headroom
-// version of the line-length assertions elsewhere.
+// version of TestTruncate_SpendsNoMoreThanTheBudget above, and of the
+// line-length assertions elsewhere.
 //
-// A line ceiling has slack in it by construction, so a line-level
-// assertion only catches a raw-byte budget for the fills with the
-// widest multiplier. Here the budget is checked against exactly what
-// it bought: a value built from a single rune must keep exactly
-// MaxBytes/EncodedBytes(r) of them, for every rune, with nothing
-// spare.
+// A line ceiling has slack in it by construction, and a LessOrEqual
+// against the budget cannot tell a budget spent exactly from one
+// spent under. Here the budget is checked against exactly what it
+// bought: a value built from a single rune must keep exactly
+// MaxBytes/EncodedBytes(r) of them, with nothing spare. A raw-byte
+// budget — cost := utf8.RuneLen(r) — fails this for every rune the
+// handlers escape.
 func TestTruncate_SpendsEncodedBytesNotRawBytes(t *testing.T) {
 	t.Parallel()

 	for name, r := range map[string]rune{
-		"plain":                'x',
-		"quote":                '"',
-		"backslash":            '\\',
-		"tab":                  '\t',
-		"newline":              '\n',
-		"carriage_return":      '\r',
-		"c0_control":           '',
-		"del":                  '',
-		"line_separator":       ' ',
-		"astral_nonprintable":  '\U0001000C',
-		"multibyte_printable":  'é',
+		"plain":           'x',
+		"quote":           '"',
+		"backslash":       '\\',
+		"tab":             '\t',
+		"newline":         '\n',
+		"carriage_return": '\r',
+		"c0_control":      '\x01',
+		"del":             '\x7f',
+		// U+2028 LINE SEPARATOR, which only the JSON handler
+		// escapes.
+		"line_separator":      ' ',
+		"astral_nonprintable": '\U0001000C',
+		"multibyte_printable": 'é',
+		// U+20AC, a three-byte printable rune, charged its own
+		// UTF-8 bytes rather than an escape.
 		"three_byte_printable": '€',
 		"emoji_printable":      '\U0001F600',
 	} {
@@ -61,12 +275,16 @@ func TestTruncate_SpendsEncodedBytesNotRawBytes(t *testing.T) {

 			got := logfield.Truncate(in, logfield.MaxBytes)

-			assert.True(
-				t, strings.HasSuffix(got, "[truncated]"),
+			require.True(
+				t, strings.HasSuffix(
+					got, logfield.TruncationMarker,
+				),
 				"a value past the budget must be marked",
 			)

-			kept := strings.TrimSuffix(got, "[truncated]")
+			kept := strings.TrimSuffix(
+				got, logfield.TruncationMarker,
+			)

 			assert.Equal(
 				t, want, utf8.RuneCountInString(kept),
@@ -80,123 +298,24 @@ func TestTruncate_SpendsEncodedBytesNotRawBytes(t *testing.T) {
 	}
 }

-// TestEncodedBytes_CoversWhatTheHandlersActuallyEmit measures the
-// charge against what slog really writes rather than against a
-// reading of its source, over both handlers internal/logger can
-// install. An undercharged rune fails here rather than quietly
-// falsifying every stated line ceiling.
-func TestEncodedBytes_CoversWhatTheHandlersActuallyEmit(t *testing.T) {
-	t.Parallel()
-
-	emitted := func(h func(*bytes.Buffer) slog.Handler, r rune) int {
-		var withValue, withoutValue bytes.Buffer
-
-		slog.New(h(&withValue)).Info("m", "v", string(r))
-		slog.New(h(&withoutValue)).Info("m", "v", "")
-
-		return withValue.Len() - withoutValue.Len()
-	}
-
-	jsonHandler := func(b *bytes.Buffer) slog.Handler {
-		return slog.NewJSONHandler(b, &slog.HandlerOptions{
-			ReplaceAttr: dropTime,
-		})
-	}
-	textHandler := func(b *bytes.Buffer) slog.Handler {
-		return slog.NewTextHandler(b, &slog.HandlerOptions{
-			ReplaceAttr: dropTime,
-		})
-	}
-
-	// Every code point below U+0800 densely — which covers all of C0,
-	// DEL, C1 and the two-byte range — plus the separators only the
-	// JSON handler escapes, plus a stratified walk across the rest of
-	// the assigned space and into the astral planes.
-	var runes []rune
-
-	for r := rune(1); r < 0x800; r++ {
-		runes = append(runes, r)
-	}
-
-	runes = append(
-		runes,
-		' ',          // LINE SEPARATOR, escaped only by the JSON handler
-		' ',          // PARAGRAPH SEPARATOR, likewise
-		rune(0xFEFF), // ZERO WIDTH NO-BREAK SPACE
-		rune(0xFFFD), // REPLACEMENT CHARACTER
-	)
-
-	for r := rune(0x800); r <= 0x10FFFF; r += 0x1D1 {
-		runes = append(runes, r)
-	}
-
-	for _, r := range runes {
-		if !utf8.ValidRune(r) {
-			continue
-		}
-
-		charged := logfield.EncodedBytes(r)
-
-		require.LessOrEqual(
-			t, emitted(jsonHandler, r), charged,
-			"json handler spends more than U+%04X is charged", r,
-		)
-		require.LessOrEqual(
-			t, emitted(textHandler, r), charged,
-			"text handler spends more than U+%04X is charged", r,
-		)
-	}
-}
-
-func dropTime(_ []string, a slog.Attr) slog.Attr {
-	if a.Key == slog.TimeKey {
-		return slog.Attr{}
-	}
-
-	return a
-}
-
-// TestTruncate_LeavesShortValuesAlone keeps the marker meaningful: a
-// value that fits is returned untouched, so a reader can tell a short
-// value from a cut one.
-func TestTruncate_LeavesShortValuesAlone(t *testing.T) {
-	t.Parallel()
-
-	const in = "Mozilla/5.0 (X11; Linux x86_64)"
-
-	assert.Equal(t, in, logfield.Truncate(in, logfield.MaxBytes))
-}
-
-// TestTruncate_DropsInvalidUTF8 covers a value that was never valid
-// UTF-8 — a SQL parameter or a header can carry one. Replacing each
-// bad byte would cost six encoded bytes apiece, so they are dropped.
-func TestTruncate_DropsInvalidUTF8(t *testing.T) {
-	t.Parallel()
-
-	got := logfield.Truncate("a\xffb\xfec", logfield.MaxBytes)
-
-	assert.Equal(t, "abc", got)
-	assert.True(t, utf8.ValidString(got))
-}
-
 // TestTruncate_NeverSplitsARune covers a cut landing inside a
-// multi-byte encoding.
+// multi-byte encoding rather than between two of them.
 func TestTruncate_NeverSplitsARune(t *testing.T) {
 	t.Parallel()

-	// A three-byte printable rune, so a small budget lands inside the
-	// encoding rather than between two of them.
+	// U+20AC, three bytes and printable, so a small budget lands
+	// inside an encoding rather than on a boundary.
 	in := strings.Repeat("€", logfield.MaxBytes)

-	for budget := 1; budget <= 16; budget++ {
+	for b := 1; b <= 16; b++ {
 		got := strings.TrimSuffix(
-			logfield.Truncate(in, budget), "[truncated]",
+			logfield.Truncate(in, b), logfield.TruncationMarker,
 		)

 		assert.True(
 			t, utf8.ValidString(got),
-			"budget %d produced invalid UTF-8", budget,
+			"budget %d produced invalid UTF-8", b,
 		)
-		assert.LessOrEqual(t, encodedCost(got), budget)
+		assert.LessOrEqual(t, encodedCost(got), b)
 	}
 }
--- a/internal/middleware/csrf.go
+++ b/internal/middleware/csrf.go
@@ -4,6 +4,7 @@ import (
 	"net/http"

 	"github.com/gorilla/csrf"
+	"sneak.berlin/go/webhooker/internal/logfield"
 )

 // CSRFToken retrieves the CSRF token from the request context.
@@ -42,9 +43,22 @@ func isClientTLS(r *http.Request) bool {
 // csrf.Secure option is set at creation time, not per-request.
 func (m *Middleware) CSRF() func(http.Handler) http.Handler {
 	csrfErrorHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// CSRF is registered ahead of RequireAuth on every route
+		// group that uses it, so this WARN is reachable by an
+		// unauthenticated client: a POST with no token to
+		// /source/<any length of any text>/edit lands here. The
+		// method and path are capped against the same budgets as
+		// the access log. remote_addr is set by net/http from the
+		// accepted connection rather than by the client, and
+		// csrf.FailureReason returns one of gorilla/csrf's own
+		// fixed error values, so neither is client-sized.
 		m.log.Warn("csrf: token validation failed",
-			"method", r.Method,
-			"path", r.URL.Path,
+			"method", logfield.Truncate(
+				r.Method, maxLogMethodBytes,
+			),
+			"path", logfield.Truncate(
+				r.URL.Path, logfield.MaxBytes,
+			),
 			"remote_addr", r.RemoteAddr,
 			"reason", csrf.FailureReason(r),
 		)
--- a/internal/middleware/logbound_test.go
+++ b/internal/middleware/logbound_test.go
@@ -0,0 +1,544 @@
+package middleware_test
+
+// This file covers the log lines OUTSIDE the access log that carry a
+// client-chosen value. accesslog_test.go bounds the one INFO line the
+// Logging middleware writes; these are the separate slog calls that
+// were never in that sweep and so never got the budget:
+//
+//   - MaxBodySize's 413 rejection, at WARN, registered ahead of
+//     RequireAuth and therefore reachable unauthenticated at a URL of
+//     the client's choosing.
+//   - CSRF's 403 rejection, at WARN, also registered ahead of
+//     RequireAuth.
+//   - The rate limiters' 429 rejection, at WARN, on the
+//     unauthenticated receiver among others.
+//   - RequireAuth's own unauthenticated-request line, at DEBUG.
+//   - RecordLoginFailure's throttle rejection, at WARN. Its cap is
+//     defensive rather than load-bearing today: chi pins the one
+//     route that calls it to the constant path "/pages/login". The
+//     method is exported and takes any *http.Request, so the test
+//     below hands it the request a caller on a parameterised route
+//     would, which is what the cap exists for.
+//
+// Every case here holds the ENCODED line to
+// middleware.MaxAccessLogLineBytes, under both handlers
+// internal/logger can install, against 8 KB of client-chosen text
+// built out of the characters those handlers escape. A budget spent
+// in raw bytes passes the plain-ASCII cases and fails the rest.
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/middleware"
+)
+
+// bodyLimitBytes is the MaxBodySize cap these tests install. Any
+// declared Content-Length above it takes the 413 branch.
+const bodyLimitBytes = 1024
+
+// declaredBodyBytes is the Content-Length an oversize request
+// declares. Nothing is actually sent: the 413 branch fires off the
+// declaration alone, which is what makes the attack free.
+const declaredBodyBytes = bodyLimitBytes * 2
+
+// receiverLimitPerMinute is the per-entrypoint receiver limit these
+// tests install. The aggregate limiter sits at ten times this, so a
+// flood stays under it and the rejections come from the
+// per-entrypoint limiter, which is the one that logs the path.
+const receiverLimitPerMinute = 8
+
+// escapeFills are the characters a client can put in a request that
+// the log handlers then escape, coming out wider than they went in.
+// A budget counted in raw bytes lets any of them buy a field several
+// times its nominal size.
+//
+// U+1000C is the case the JSON handler alone does not reach: it is
+// unassigned, so it is non-printable, and strconv.Quote spells a
+// non-printable rune at or above U+10000 as a ten-byte \UXXXXXXXX
+// while the JSON handler passes its four UTF-8 bytes through. Only
+// the text-handler shape of these tests holds that charge honest.
+func escapeFills() map[string]string {
+	return map[string]string{
+		"plain":     "x",
+		"quote":     `"`,
+		"backslash": `\`,
+		"tab":       "\t",
+		"newline":   "\n",
+		// A C0 control neither handler has a short escape for, so
+		// each one costs six bytes on the line against the single
+		// byte it cost to send. This is the widest multiplier a
+		// client can drive, and the case a raw-byte budget breaks
+		// on first.
+		//
+		// This fill is load-bearing, not decoration. Budgeting raw
+		// bytes instead of encoded is caught by this fill alone,
+		// and only under the JSON handler, at 3,072 bytes against
+		// the 2,560 ceiling. Drop it and that mutation passes.
+		"control": "\x01",
+		"astral":  "\U0001000C",
+	}
+}
+
+// logHandlers are the two handlers internal/logger can install: the
+// JSON one, and the text one it selects when stderr is a tty. They do
+// not escape alike, and MaxAccessLogLineBytes is quoted unqualified,
+// so every case runs through both.
+func logHandlers() map[string]func(
+	io.Writer, *slog.HandlerOptions,
+) slog.Handler {
+	return map[string]func(
+		io.Writer, *slog.HandlerOptions,
+	) slog.Handler{
+		"json": func(
+			w io.Writer, o *slog.HandlerOptions,
+		) slog.Handler {
+			return slog.NewJSONHandler(w, o)
+		},
+		"text": func(
+			w io.Writer, o *slog.HandlerOptions,
+		) slog.Handler {
+			return slog.NewTextHandler(w, o)
+		},
+	}
+}
+
+// oversizedPathSegment builds an 8 KB client-chosen path segment out
+// of repetitions of ch, percent-encoded so it survives URL parsing
+// into r.URL.Path the way it would arriving off a socket.
+//
+// Both markers sit at the END, past every budget, so their absence
+// from the log is what proves the value was cut rather than merely
+// being short. The leading 'x' keeps the segment non-empty for fills
+// that a parser might otherwise fold away.
+func oversizedPathSegment(ch string) string {
+	return url.PathEscape(
+		"x" + strings.Repeat(ch, oversizedSegmentBytes) +
+			attackerMarker + tailMarker,
+	)
+}
+
+// capturingLogger returns a logger at DEBUG writing into the returned
+// buffer through the named handler.
+func capturingLogger(
+	newHandler func(io.Writer, *slog.HandlerOptions) slog.Handler,
+) (*slog.Logger, *bytes.Buffer) {
+	buf := new(bytes.Buffer)
+	opts := &slog.HandlerOptions{Level: slog.LevelDebug}
+
+	return slog.New(newHandler(buf, opts)), buf
+}
+
+// capturingBoundMiddleware builds a Middleware with a real session
+// manager (CSRF needs its key, RequireAuth needs its store) whose log
+// is captured at DEBUG.
+func capturingBoundMiddleware(
+	t *testing.T,
+	newHandler func(io.Writer, *slog.HandlerOptions) slog.Handler,
+) (*middleware.Middleware, *bytes.Buffer) {
+	t.Helper()
+
+	log, buf := capturingLogger(newHandler)
+
+	cfg := &config.Config{
+		Environment:       config.EnvironmentDev,
+		ReceiverRateLimit: receiverLimitPerMinute,
+	}
+
+	sess := newTestSessionManager(cfg, log, nil)
+
+	return middleware.NewForTest(log, cfg, sess), buf
+}
+
+// unreachable is a next-handler that fails the test if the middleware
+// under test let the request through. Every site here rejects.
+func unreachable(t *testing.T) http.Handler {
+	t.Helper()
+
+	return http.HandlerFunc(func(http.ResponseWriter, *http.Request) {
+		assert.Fail(t, "rejected request reached the next handler")
+	})
+}
+
+// logSite is one non-access-log call site that logs a client-chosen
+// path. drive sends requests at it that all take the rejecting
+// branch; linesPerRequest is how many log lines one such request
+// produces there.
+type logSite struct {
+	// build wraps the site's middleware around a handler that must
+	// not be reached.
+	build func(
+		t *testing.T, m *middleware.Middleware,
+	) http.Handler
+	// send issues one request for the given client-chosen path and
+	// returns the status. Some sites need a warm-up request before
+	// they reject, which send performs itself.
+	send func(h http.Handler, path string) int
+	// wantStatus is the status the rejecting branch answers with.
+	wantStatus int
+}
+
+// postOversize sends a POST whose declared Content-Length exceeds the
+// body limit without sending a body, which is the whole cost of the
+// attack on the MaxBodySize branch.
+func postOversize(h http.Handler, path string) int {
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodPost, path, nil,
+	)
+	req.ContentLength = declaredBodyBytes
+	req.Header.Set(
+		"Content-Type", "application/x-www-form-urlencoded",
+	)
+
+	w := httptest.NewRecorder()
+	h.ServeHTTP(w, req)
+
+	return w.Code
+}
+
+// postNoToken sends a POST carrying no CSRF token and no session
+// cookie, which is what an unauthenticated client sends.
+func postNoToken(h http.Handler, path string) int {
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodPost, path,
+		strings.NewReader(""),
+	)
+	req.Header.Set(
+		"Content-Type", "application/x-www-form-urlencoded",
+	)
+
+	w := httptest.NewRecorder()
+	h.ServeHTTP(w, req)
+
+	return w.Code
+}
+
+// getNoSession sends a GET with no session cookie.
+func getNoSession(h http.Handler, path string) int {
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, path, nil,
+	)
+
+	w := httptest.NewRecorder()
+	h.ServeHTTP(w, req)
+
+	return w.Code
+}
+
+// logSites enumerates the call sites under test.
+func logSites() map[string]logSite {
+	return map[string]logSite{
+		// The site this file exists for: WARN, on by default, and
+		// registered ahead of RequireAuth.
+		"maxbodysize 413": {
+			build: func(
+				t *testing.T, m *middleware.Middleware,
+			) http.Handler {
+				t.Helper()
+
+				return m.MaxBodySize(bodyLimitBytes)(
+					unreachable(t),
+				)
+			},
+			send:       postOversize,
+			wantStatus: http.StatusRequestEntityTooLarge,
+		},
+		// Also ahead of RequireAuth, also WARN.
+		"csrf 403": {
+			build: func(
+				t *testing.T, m *middleware.Middleware,
+			) http.Handler {
+				t.Helper()
+
+				return m.CSRF()(unreachable(t))
+			},
+			send:       postNoToken,
+			wantStatus: http.StatusForbidden,
+		},
+		// The per-entrypoint receiver limiter, unauthenticated. Its
+		// bucket is keyed on the path, so the first request through a
+		// fresh path is served and only the ones after it are
+		// rejected; sendUntilLimited absorbs that.
+		"receiver rate limit 429": {
+			build: func(
+				t *testing.T, m *middleware.Middleware,
+			) http.Handler {
+				t.Helper()
+
+				return m.ReceiverRateLimit()(okHandler())
+			},
+			send:       sendUntilLimited,
+			wantStatus: http.StatusTooManyRequests,
+		},
+		// RequireAuth's own line. DEBUG is off in production by
+		// default, but turning it on to diagnose a flood must not
+		// restore an unbounded write.
+		"requireauth redirect": {
+			build: func(
+				t *testing.T, m *middleware.Middleware,
+			) http.Handler {
+				t.Helper()
+
+				return m.RequireAuth()(unreachable(t))
+			},
+			send:       getNoSession,
+			wantStatus: http.StatusSeeOther,
+		},
+	}
+}
+
+// sendUntilLimited drives the per-entrypoint receiver limiter past
+// its allowance on one path and returns the status of the rejected
+// request. Every request before the last is served, and only the last
+// one logs.
+func sendUntilLimited(h http.Handler, path string) int {
+	code := http.StatusOK
+
+	for range receiverLimitPerMinute + 1 {
+		req := httptest.NewRequestWithContext(
+			context.Background(), http.MethodPost, path, nil,
+		)
+		req.RemoteAddr = "203.0.113.7:5555"
+
+		w := httptest.NewRecorder()
+		h.ServeHTTP(w, req)
+		code = w.Code
+	}
+
+	return code
+}
+
+// logLines splits the captured buffer into non-empty lines, holding
+// each to bound bytes.
+func logLines(t *testing.T, buf *bytes.Buffer, bound int) []string {
+	t.Helper()
+
+	var lines []string
+
+	for line := range strings.SplitSeq(
+		strings.TrimSpace(buf.String()), "\n",
+	) {
+		if line == "" {
+			continue
+		}
+
+		require.LessOrEqual(
+			t, len(line), bound,
+			"log line exceeded its bound: %s", line,
+		)
+
+		lines = append(lines, line)
+	}
+
+	return lines
+}
+
+// assertNoClientText fails if any marker from the far end of the
+// client-chosen input survived into the log. Their absence is what
+// distinguishes a real cut from a value that merely happened to be
+// short.
+func assertNoClientText(t *testing.T, buf *bytes.Buffer) {
+	t.Helper()
+
+	assert.NotContains(
+		t, buf.String(), attackerMarker,
+		"log carried attacker-chosen text",
+	)
+	assert.NotContains(
+		t, buf.String(), tailMarker,
+		"log carried the tail of the attacker-chosen text",
+	)
+}
+
+// TestLogLines_ClientChosenPathDoesNotSizeTheLine points 8 KB of
+// client-chosen path at each non-access-log call site that logs one,
+// through both handlers and through every character those handlers
+// escape, and holds the resulting line to MaxAccessLogLineBytes.
+//
+// Removing any one of the logfield.Truncate calls at those sites
+// fails this test: the line grows to roughly the size of the input,
+// or to several times it on the escaping fills.
+func TestLogLines_ClientChosenPathDoesNotSizeTheLine(t *testing.T) {
+	t.Parallel()
+
+	for siteName, site := range logSites() {
+		for handlerName, newHandler := range logHandlers() {
+			for fillName, fill := range escapeFills() {
+				name := siteName + "/" + handlerName + "/" + fillName
+
+				t.Run(name, func(t *testing.T) {
+					t.Parallel()
+
+					m, buf := capturingBoundMiddleware(
+						t, newHandler,
+					)
+
+					path := "/source/" +
+						oversizedPathSegment(fill) + "/edit"
+
+					assert.Equal(
+						t,
+						site.wantStatus,
+						site.send(site.build(t, m), path),
+					)
+
+					lines := logLines(
+						t, buf,
+						middleware.MaxAccessLogLineBytes,
+					)
+					require.NotEmpty(
+						t, lines,
+						"the site under test logged nothing, "+
+							"so the bound proves nothing",
+					)
+					assertNoClientText(t, buf)
+				})
+			}
+		}
+	}
+}
+
+// TestLoginThrottle_LogLineDoesNotTrackPathSize pins the cap on
+// RecordLoginFailure's "login failure limit exceeded" WARN line.
+//
+// That site does not fit logSites above: it is not a middleware
+// wrapping a handler but an exported method the login handler calls,
+// and the only route that calls it today is chi's static
+// "/pages/login", so no request through the mux can widen the line.
+// Driving the method directly is therefore the whole point rather
+// than a shortcut — it is exactly the call a second caller on a route
+// with a URL parameter would make, and without this test removing the
+// logfield.Truncate there fails nothing.
+func TestLoginThrottle_LogLineDoesNotTrackPathSize(t *testing.T) {
+	t.Parallel()
+
+	for handlerName, newHandler := range logHandlers() {
+		for fillName, fill := range escapeFills() {
+			t.Run(handlerName+"/"+fillName, func(t *testing.T) {
+				t.Parallel()
+
+				m, buf := capturingBoundMiddleware(
+					t, newHandler,
+				)
+
+				req := httptest.NewRequestWithContext(
+					context.Background(),
+					http.MethodPost,
+					"/source/"+
+						oversizedPathSegment(fill)+"/login",
+					nil,
+				)
+				req.RemoteAddr = "203.0.113.9:5555"
+
+				// The budget is spent per client and username,
+				// so one more failure than the budget allows is
+				// what takes the throttled branch.
+				var throttled bool
+				for range middleware.LoginRateLimitConst + 1 {
+					throttled = m.RecordLoginFailure(
+						req, "someone",
+					)
+				}
+
+				require.True(
+					t, throttled,
+					"the throttled branch never ran, so the "+
+						"bound proves nothing",
+				)
+
+				lines := logLines(
+					t, buf, middleware.MaxAccessLogLineBytes,
+				)
+				require.NotEmpty(t, lines)
+				assertNoClientText(t, buf)
+			})
+		}
+	}
+}
+
+// TestMaxBodySize_FloodOfOversizePathsDoesNotGrowTheLog is the
+// flood shape from the issue: an unauthenticated client posting
+// oversize declarations at invented 8 KB paths, as fast as it likes.
+//
+// It asserts the property directly rather than by proxy — the bytes
+// the flood writes to the operator's log do not track the bytes the
+// flood sent. The same flood at a one-character path is the control:
+// 8 KB of extra input per request buys at most the field budget, not
+// 8 KB of log.
+func TestMaxBodySize_FloodOfOversizePathsDoesNotGrowTheLog(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	for handlerName, newHandler := range logHandlers() {
+		for fillName, fill := range escapeFills() {
+			t.Run(handlerName+"/"+fillName, func(t *testing.T) {
+				t.Parallel()
+
+				flood := func(segment func(i int) string) int {
+					m, buf := capturingBoundMiddleware(
+						t, newHandler,
+					)
+					h := m.MaxBodySize(bodyLimitBytes)(
+						unreachable(t),
+					)
+
+					for i := range floodRequests {
+						assert.Equal(
+							t,
+							http.StatusRequestEntityTooLarge,
+							postOversize(
+								h,
+								"/source/"+segment(i)+"/edit",
+							),
+						)
+					}
+
+					lines := logLines(
+						t, buf,
+						middleware.MaxAccessLogLineBytes,
+					)
+					require.Len(t, lines, floodRequests)
+					assertNoClientText(t, buf)
+
+					return buf.Len()
+				}
+
+				sent := oversizedSegmentBytes * floodRequests
+
+				oversize := flood(func(i int) string {
+					return oversizedPathSegment(fill) +
+						strings.Repeat("y", i)
+				})
+				control := flood(func(i int) string {
+					return "a" + strings.Repeat("y", i)
+				})
+
+				// The whole point: 8 KB per request of extra
+				// client-chosen input bought a bounded amount of
+				// log, not a proportional amount.
+				assert.Less(
+					t, oversize-control, sent/2,
+					"log volume tracked the size of the flood's "+
+						"input",
+				)
+				assert.LessOrEqual(
+					t,
+					oversize,
+					floodRequests*
+						middleware.MaxAccessLogLineBytes,
+				)
+			})
+		}
+	}
+}
--- a/internal/middleware/loginguard.go
+++ b/internal/middleware/loginguard.go
@@ -7,6 +7,8 @@ import (
 	"net/http"
 	"sync"
 	"time"
+
+	"sneak.berlin/go/webhooker/internal/logfield"
 )

 const (
@@ -173,10 +175,38 @@ func newLoginGuard(
 // acquire reserves a verification slot, waiting up to the guard's
 // wait for one. It reports false when the queue of waiters is
 // already full, when no slot became available in time, or when the
-// request was cancelled first; the caller must then answer 503
-// without verifying anything. The returned function releases the
+// request was cancelled while waiting; the caller must then answer
+// 503 without verifying anything. The returned function releases the
 // slot and must be called exactly once.
+//
+// ctx is consulted only once the request has to wait: a slot that is
+// free on arrival is handed out without looking at it, so an
+// already-cancelled request can be granted one. That is deliberate
+// and matches lifecycle.waitDone — the caller abandons the work on
+// its own ctx and releases the slot immediately, so nothing is spent
+// on it, and refusing instead would mean shedding a request with
+// capacity standing free.
 func (g *loginGuard) acquire(ctx context.Context) (func(), bool) {
+	// A free slot is taken before any timer is armed, and before a
+	// queue place is claimed: a request that never waits is not a
+	// waiter. Without this preamble the bounded select below can find
+	// its slot send and an already-expired timer ready at the same
+	// time, and Go picks among ready cases uniformly at random — so a
+	// process descheduled for longer than the wait sheds a request
+	// with slots standing free, which is precisely when shedding is
+	// least defensible.
+	//
+	// This cannot let a late arrival barge past a queued waiter. A
+	// waiter can only be parked on a FULL buffer, and a release
+	// refills that buffer from the head of the send queue under the
+	// channel lock, so the buffer never appears non-full while anyone
+	// is parked and this send fails whenever there is a waiter.
+	select {
+	case g.slots <- struct{}{}:
+		return func() { <-g.slots }, true
+	default:
+	}
+
 	// Shedding past the queue depth is what keeps waiting memory
 	// bounded; the wait alone only bounds how long one waiter holds
 	// its parsed form, not how many hold one at once.
@@ -344,8 +374,17 @@ func (m *Middleware) RecordLoginFailure(
 ) bool {
 	throttled := m.guard().fail(m.clientKey(r), username)
 	if throttled {
+		// Truncated even though chi pins this route's path to
+		// the 12-byte constant "/pages/login": RecordLoginFailure
+		// is exported and takes any *http.Request, so a caller on
+		// a route with a URL parameter would otherwise widen this
+		// line. logbound_test.go pins the cap by making exactly
+		// that call, since no request through the mux can.
 		m.log.Warn(
-			"login failure limit exceeded", "path", r.URL.Path,
+			"login failure limit exceeded",
+			"path", logfield.Truncate(
+				r.URL.Path, logfield.MaxBytes,
+			),
 		)
 	}

--- a/internal/middleware/loginguard_test.go
+++ b/internal/middleware/loginguard_test.go
@@ -29,6 +29,15 @@ const (

 	guardClient = "198.51.100.7"
 	guardUser   = "admin"
+
+	// racePasses is how many times a both-cases-ready select race is
+	// run. A pass can only go the wrong way once the zero-duration
+	// timer has fired, so the per-pass detection probability is
+	// somewhere below 1/2 rather than exactly it; the bound that
+	// matters is that passes are independent, so a regression that
+	// survives is exponentially unlikely in N. The test still waits
+	// on nothing.
+	racePasses = 1000
 )

 // newGuard builds a guard with production-shaped defaults and the
@@ -224,21 +233,71 @@ func TestLoginGuard_SemaphoreBoundsConcurrentVerifications(
 	const (
 		concurrency = 2
 		workers     = 12
+
+		// rendezvousDeadlock is the deadlock guard described below.
+		// It is orders of magnitude longer than any scheduling delay,
+		// so it never decides the result, and well inside script/test's
+		// 30s timeout, so a wedge fails on the assertion instead of
+		// blowing the package timeout.
+		rendezvousDeadlock = 5 * time.Second
 	)

 	g := newGuard(middleware.LoginFailureMaxKeysConst, concurrency)

 	var (
-		mu      sync.Mutex
-		inside  int
-		highest int
-		wg      sync.WaitGroup
+		mu       sync.Mutex
+		inside   int
+		highest  int
+		wg       sync.WaitGroup
+		recorded sync.WaitGroup
+		once     sync.Once
 	)

+	// Slot holders rendezvous instead of sleeping, and they hold until
+	// every worker has been answered. A sleep only makes overlap
+	// likely — on a host loaded enough to deschedule a goroutine for
+	// longer than the sleep the workers serialise and the maximum
+	// observed comes back as 1 — so the rendezvous is what makes the
+	// overlap a fact rather than a race won.
+	//
+	// The barrier must not open at the concurrency-th holder, which
+	// would fix the lower bound at the cost of the upper one this test
+	// exists to enforce: holders would leave as soon as the count
+	// reached concurrency, so a guard admitting extra requests would
+	// let them arrive after the first holders had already left and
+	// highest would report concurrency however many were really let
+	// in. It opens instead once every worker's acquire has returned
+	// and any slot it won has been counted, so under a broken guard
+	// every admitted worker is inside simultaneously and highest is
+	// the true maximum. Under a correct guard the refused workers
+	// return within the guard's own wait, which decides nothing beyond
+	// how long that takes.
+	overlapped := make(chan struct{})
+	closeOverlapped := func() {
+		once.Do(func() { close(overlapped) })
+	}
+
+	// Deadlock guard, not a timing margin: no assertion depends on its
+	// length, and the only way to reach it is a worker that never
+	// returns from acquire at all. It is here so that such a wedge
+	// fails legibly on the assertion below instead of hanging until
+	// the package test timeout.
+	abandon := time.AfterFunc(rendezvousDeadlock, closeOverlapped)
+	defer abandon.Stop()
+
+	recorded.Add(workers)
+
+	go func() {
+		recorded.Wait()
+		closeOverlapped()
+	}()
+
 	for range workers {
 		wg.Go(func() {
 			release, ok := g.AcquireForTest(context.Background())
 			if !ok {
+				recorded.Done()
+
 				return
 			}

@@ -253,9 +312,12 @@ func TestLoginGuard_SemaphoreBoundsConcurrentVerifications(

 			mu.Unlock()

-			// Hold the slot long enough that the other workers are
-			// certainly contending for it.
-			time.Sleep(10 * time.Millisecond)
+			// Counted before signalling, so the barrier can never open
+			// while an admitted worker is still on its way to being
+			// counted.
+			recorded.Done()
+
+			<-overlapped

 			mu.Lock()
 			inside--
@@ -278,6 +340,14 @@ func TestLoginGuard_SemaphoreBoundsConcurrentVerifications(
 // what happens when every slot is taken for longer than the wait: the
 // request is refused, so the caller answers 503 without allocating
 // another 64 MB hash.
+//
+// Neither half of this rides on the wait being long enough. The
+// refusal holds the only slot across the whole of the second call, so
+// there is no wait it could get lucky with — the wait fixes only how
+// long the refusal takes, not whether it happens. The reuse after
+// release is settled by acquire's non-blocking preamble, which is
+// pinned separately by TestLoginGuard_FreeSlotBeatsAnExpiredWait. So
+// the wait below is sized to keep the test quick, not to win a race.
 func TestLoginGuard_SaturatedSemaphoreRefusesRatherThanQueueing(
 	t *testing.T,
 ) {
@@ -305,13 +375,58 @@ func TestLoginGuard_SaturatedSemaphoreRefusesRatherThanQueueing(
 	release()

 	release, ok = g.AcquireForTest(context.Background())
-	assert.True(
+
+	// require, not assert: acquire returns a nil release alongside a
+	// false ok, so calling it after a non-fatal assertion turns one
+	// failed test into a segfault that takes the whole package test
+	// binary down. Every assertion whose value is dereferenced later
+	// has to stop the test.
+	require.True(
 		t, ok, "the slot must be reusable once released",
 	)

 	release()
 }

+// TestLoginGuard_FreeSlotBeatsAnExpiredWait is the determinism this
+// file used to lack. acquire selects over a slot send and a wait
+// timer, and Go chooses among ready cases uniformly at random, so a
+// call made after the timer had already fired was a coin flip: on a
+// loaded host the previous test's third acquire could be refused
+// with its slot standing free, and then dereference the nil release
+// it got back.
+//
+// The wait here is already elapsed on arrival, which is the worst
+// case that scheduling can produce, so a free slot must still be
+// granted every time. Without acquire's non-blocking preamble each
+// pass is an independent coin flip and the loop fails within a few
+// passes; with it the property holds by construction and no wall
+// clock is involved.
+func TestLoginGuard_FreeSlotBeatsAnExpiredWait(t *testing.T) {
+	t.Parallel()
+
+	g := middleware.NewLoginGuardForTest(
+		middleware.LoginRateLimitConst,
+		guardInterval,
+		middleware.LoginFailureMaxKeysConst,
+		1,
+		middleware.PasswordVerifyMaxWaitersConst,
+		0,
+	)
+
+	for pass := range racePasses {
+		release, ok := g.AcquireForTest(context.Background())
+		require.Truef(
+			t, ok,
+			"pass %d was refused a slot that was free; an expired "+
+				"wait must never beat an available slot",
+			pass,
+		)
+
+		release()
+	}
+}
+
 // TestLoginGuard_AcquireHonoursCancellation proves a client that
 // disconnects while queued frees its place immediately instead of
 // holding it for the full wait.
@@ -388,13 +503,20 @@ func TestLoginGuard_ShedsPastTheQueueCap(t *testing.T) {
 		neverElapses = time.Minute

 		// The probe carries its own deadline, so a guard that queues
-		// the probe instead of shedding it fails on the elapsed time
-		// rather than hanging until the package test timeout.
-		probeWait = 200 * time.Millisecond
-
-		// Shedding takes no measurable time; queueing takes the whole
-		// probeWait. Anything under half of it is unambiguous.
-		shedFast = probeWait / 2
+		// the probe instead of shedding it fails here rather than
+		// hanging until the package test timeout.
+		//
+		// This is a patience budget, not a margin to be won. A shed
+		// returns in microseconds and a probe that queued instead
+		// would not return for neverElapses, so the two are a whole
+		// minute apart and any budget between them separates them. It
+		// is set far above any scheduling stall a loaded host can
+		// produce, because the previous 200 ms — and the 100 ms
+		// elapsed-time assertion it fed — bounded the latency of a
+		// goroutine hand-off, which is a false red waiting to happen
+		// on the machine this suite runs on. What actually proves the
+		// probe was not queued is the queue depth asserted below.
+		probePatience = 5 * time.Second
 	)

 	g := middleware.NewLoginGuardForTest(
@@ -413,22 +535,17 @@ func TestLoginGuard_ShedsPastTheQueueCap(t *testing.T) {
 	defer release()
 	defer fillQueue(t, g, maxWaiters)()

-	got := probeQueueCap(g, probeWait)
+	granted, answered := probeQueueCap(g, probePatience)

-	require.NotNil(
-		t, got,
+	require.True(
+		t, answered,
 		"a request arriving past the queue cap is still waiting to "+
 			"be queued; it must have been shed",
 	)
 	assert.False(
-		t, got.ok,
+		t, granted,
 		"a request arriving past the queue cap must be shed",
 	)
-	assert.Less(
-		t, got.elapsed, shedFast,
-		"shedding must be immediate; waiting for a place in the "+
-			"queue is the memory growth this bounds",
-	)
 	assert.Equal(
 		t, maxWaiters, g.QueuedWaitersForTest(),
 		"a shed request must not have grown the queue",
@@ -458,10 +575,14 @@ func fillQueue(
 		})
 	}

+	// Patience budget, not a margin: the waiters park in microseconds
+	// and nothing releases them, so the only way to exhaust this is a
+	// guard that never queues. One second is the same order as the
+	// scheduling stalls this suite has to survive, so it is not one.
 	require.Eventually(
 		t,
 		func() bool { return g.QueuedWaitersForTest() == n },
-		time.Second, time.Millisecond,
+		5*time.Second, time.Millisecond,
 		"the waiters must reach the queue before the cap is tested",
 	)

@@ -471,41 +592,38 @@ func fillQueue(
 	}
 }

-// probeResult is what the queue-cap probe reports: whether it got a
-// slot, and how long it took to find out.
-type probeResult struct {
-	ok      bool
-	elapsed time.Duration
-}
-
-// probeQueueCap acquires from another goroutine and reports the
-// result, or nil if the call was still blocked after wait.
+// probeQueueCap acquires from another goroutine. It reports, in
+// order, whether the call was granted a slot and whether it was
+// answered at all within wait; a call that never returned reports
+// false for both.
 //
 // It runs off the test goroutine deliberately. Joining a full queue
 // is not cancellable by context — refusing to join is the property
 // under test — so a guard that fails this would otherwise hang the
 // package until the test timeout instead of failing here.
+//
+// It reports no elapsed time. Timing a goroutine hand-off measures
+// the host, not the guard, and the caller distinguishes shedding from
+// queueing by the queue depth instead.
 func probeQueueCap(
 	g *middleware.LoginGuard,
 	wait time.Duration,
-) *probeResult {
-	probed := make(chan probeResult, 1)
+) (bool, bool) {
+	probed := make(chan bool, 1)

 	go func() {
-		start := time.Now()
-
 		release, ok := g.AcquireForTest(context.Background())
 		if ok {
 			release()
 		}

-		probed <- probeResult{ok: ok, elapsed: time.Since(start)}
+		probed <- ok
 	}()

 	select {
 	case result := <-probed:
-		return &result
+		return result, true
 	case <-time.After(wait):
-		return nil
+		return false, false
 	}
 }
--- a/internal/middleware/middleware.go
+++ b/internal/middleware/middleware.go
@@ -57,7 +57,7 @@ const (
 	// MaxAccessLogLineBytes is the ceiling on one JSON access log line,
 	// and the number an operator multiplies by the request rate to size
 	// log storage. It is not an observation of a sample: it is the sum
-	// of the field budgets, each of which logfield.Truncate enforces in
+	// of the budgets above, each of which logfield.Truncate enforces in
 	// ENCODED bytes, plus the part of the line no client can influence.
 	//
 	//	url, useragent, referer   3*(512+11) = 1569
@@ -85,21 +85,64 @@ const (
 	// The text handler's fixed portion is 286, the smaller of the two,
 	// which puts its worst case at 2037.
 	//
-	// The access log is the widest line this service writes that
-	// carries client-chosen text, so the figure is also the ceiling on
-	// the other writer that does: the GORM adapter in
-	// internal/gormlog, whose widest line spends two logfield.MaxBytes
-	// budgets (the interpolated SQL and the driver error) against a
-	// fixed portion smaller than this one's.
-	// internal/gormlog/gormlog_test.go asserts that against this
-	// constant directly rather than leaving it as arithmetic.
+	// It is also the ceiling on every OTHER line this service writes
+	// THROUGH SLOG that carries text an UNAUTHENTICATED client
+	// supplies. Those lines — the MaxBodySize rejection, the CSRF
+	// rejection, the rate-limit rejection, the unauthenticated-request
+	// and unknown-entrypoint DEBUG lines, the failed-login DEBUG
+	// lines, and the two login-throttle WARN lines ("login failure
+	// limit exceeded" in loginguard.go and "password verification
+	// capacity exhausted" in internal/handlers/auth.go) — spend the
+	// same per-field budgets, and each carries strictly fewer
+	// client-supplied fields than the access log does,
+	// so none of them can reach a width the access log cannot. That is
+	// asserted directly, per line and under both handlers, rather than
+	// left to the reasoning: see logbound_test.go in this package and
+	// in internal/handlers.
 	//
-	// It is not the widest line the service can write. A handler panic
-	// arrives through net/http's nil ErrorLog as one record carrying a
-	// whole goroutine stack, measured at 2,772 bytes. That value is
-	// the runtime's, not a client's, so it is a carve-out this ceiling
-	// states rather than covers; see README.md and
-	// https://git.eeqj.de/sneak/webhooker/issues/187.
+	// The two login-throttle lines are capped defensively: chi pins
+	// their route to the constant path "/pages/login", so no request
+	// through the mux can widen either one. Their assertions call
+	// RecordLoginFailure and the login handler directly with the path
+	// a caller on a parameterised route would supply, which is the
+	// only way those caps can be pinned at all.
+	//
+	// One writer in that set is not a handler's own slog call. The
+	// GORM adapter in internal/gormlog logs the statement with the
+	// client-chosen parameter already interpolated into it, which on
+	// the receiver and login lookups is exactly the value the budgets
+	// above exist for. Its widest line spends two logfield.MaxBytes
+	// budgets — the statement and the driver error — against a fixed
+	// portion smaller than this one's, and
+	// internal/gormlog/gormlog_test.go asserts every line it emits
+	// against this constant directly rather than leaving it as
+	// arithmetic.
+	//
+	// What it does NOT cover, so that the figure above is not read as
+	// more than it is:
+	//
+	//   - Lines carrying an AUTHENTICATED operator's own input, which
+	//     are not truncated at all: the webhook name on "webhook
+	//     created" and the target host on "target URL blocked by SSRF
+	//     protection" (both internal/handlers/source_management.go),
+	//     and target_name in internal/delivery/engine.go and
+	//     target_http.go. Each is bounded only by the 1 MB form body
+	//     cap, so a 100 KB name writes one line of roughly 600 KB.
+	//     Deliberate: truncating the operator's own configuration
+	//     echoed back costs debuggability against no adversary.
+	//   - The "log" delivery target, which exists to write the whole
+	//     inbound event to the log. Deliberate; see
+	//     internal/delivery/target_log.go.
+	//   - The widest line the service can write, which is neither an
+	//     access log line nor client-chosen. A handler panic arrives
+	//     through net/http's nil ErrorLog as one record carrying a
+	//     whole goroutine stack, above this figure — measured at
+	//     roughly 2,770 bytes. The exact width is not an invariant: it
+	//     moves with the goroutine number and with the source paths
+	//     baked into the stack. That it exceeds this ceiling does not
+	//     move. The value is the runtime's, not a client's; see
+	//     README.md and
+	//     https://git.eeqj.de/sneak/webhooker/issues/187.
 	MaxAccessLogLineBytes = 2560
 )

@@ -351,10 +394,21 @@ func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
 			// session lands here and is sent back to the login
 			// page.
 			if !s.session.IsAuthenticated(sess) {
+				// This is the unauthenticated branch, so both
+				// fields are entirely client-chosen and neither
+				// is bounded by anything the router did. DEBUG
+				// is off by default, but turning it on to
+				// diagnose a problem must not hand a client an
+				// unbounded write into the log, so the same
+				// budgets apply here as in the access log.
 				s.log.Debug(
 					"auth middleware: unauthenticated request",
-					"path", r.URL.Path,
-					"method", r.Method,
+					"path", logfield.Truncate(
+						r.URL.Path, logfield.MaxBytes,
+					),
+					"method", logfield.Truncate(
+						r.Method, maxLogMethodBytes,
+					),
 				)
 				http.Redirect(
 					w, r, "/pages/login", http.StatusSeeOther,
@@ -514,10 +568,26 @@ func (s *Middleware) MaxBodySize(
 			}

 			if r.ContentLength > maxBytes {
+				// This runs ahead of RequireAuth (see
+				// setupUserRoutes and friends in
+				// internal/server/routes.go), so an
+				// unauthenticated client reaches it with a path
+				// of its own choosing and its own length —
+				// POST /source/<8 KB>/edit with an oversize
+				// declared Content-Length costs nothing to
+				// send. At WARN, on by default, that is a
+				// write into the operator's log sized by the
+				// attacker unless the path is capped. Same
+				// budgets as the access log, so this line
+				// cannot be wider than that one.
 				s.log.Warn(
 					"request body exceeds limit",
-					"method", r.Method,
-					"path", r.URL.Path,
+					"method", logfield.Truncate(
+						r.Method, maxLogMethodBytes,
+					),
+					"path", logfield.Truncate(
+						r.URL.Path, logfield.MaxBytes,
+					),
 					"content_length", r.ContentLength,
 					"limit", maxBytes,
 				)
--- a/internal/middleware/middleware_test.go
+++ b/internal/middleware/middleware_test.go
@@ -57,7 +57,21 @@ func testMiddlewareWithSessionClock(
 		SessionIdleTimeout: idleTimeout,
 	}

-	// Create a real session manager with a known key
+	sessManager := newTestSessionManager(cfg, log, clock)
+
+	m := middleware.NewForTest(log, cfg, sessManager)
+
+	return m, sessManager, clock
+}
+
+// newTestSessionManager builds the real session.Session the
+// middleware tests run against: an in-memory cookie store with a
+// known key, and optionally a manually advanced clock.
+func newTestSessionManager(
+	cfg *config.Config,
+	log *slog.Logger,
+	clock *fakeClock,
+) *session.Session {
 	key := make([]byte, testKeySize)

 	for i := range key {
@@ -79,11 +93,7 @@ func testMiddlewareWithSessionClock(
 		now = clock.Now
 	}

-	sessManager := session.NewForTest(store, cfg, log, key, now)
-
-	m := middleware.NewForTest(log, cfg, sessManager)
-
-	return m, sessManager, clock
+	return session.NewForTest(store, cfg, log, key, now)
 }

 // fakeClock is a manually advanced clock, so session expiry can be
--- a/internal/middleware/ratelimit.go
+++ b/internal/middleware/ratelimit.go
@@ -9,6 +9,7 @@ import (
 	"time"

 	"github.com/go-chi/httprate"
+	"sneak.berlin/go/webhooker/internal/logfield"
 )

 const (
@@ -225,11 +226,22 @@ func (m *Middleware) clientKey(r *http.Request) string {
 // rejection with logMessage and answers with responseMessage.
 // httprate adds the Retry-After header (RFC 6585). The aggregate
 // receiver limiter uses floodTooManyRequests instead.
+//
+// The path is capped against the same budget as the access log's url
+// field. The per-entrypoint receiver limiter is unauthenticated and
+// its path is a client-chosen segment of client-chosen length, so at
+// WARN an uncapped path would let a sender pick the size of the line
+// it writes — the same defect the access log capping closed.
 func (m *Middleware) tooManyRequests(
 	logMessage, responseMessage string,
 ) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		m.log.Warn(logMessage, "path", r.URL.Path)
+		m.log.Warn(
+			logMessage,
+			"path", logfield.Truncate(
+				r.URL.Path, logfield.MaxBytes,
+			),
+		)
 		http.Error(w, responseMessage, http.StatusTooManyRequests)
 	}
 }
--- a/internal/server/routes.go
+++ b/internal/server/routes.go
@@ -14,6 +14,28 @@ import (
 // maxFormBodySize is the maximum allowed request body size (in
 // bytes) for form POST endpoints. 1 MB is generous for any form
 // submission while preventing abuse from oversized payloads.
+//
+// Every route group below installs MaxBodySize(maxFormBodySize) as
+// its FIRST middleware, ahead of both CSRF and RequireAuth. Both
+// orderings are deliberate.
+//
+// Ahead of CSRF because gorilla/csrf parses the form. The cap has to
+// be installed before anything reads the body, or the parse runs
+// under net/http's 10 MB default instead of this one.
+//
+// Ahead of RequireAuth because an oversize body should be refused
+// before the request buys a cookie decrypt, a session load and the
+// database read behind it. Rejecting first is the cheaper failure,
+// and it is the ordering that keeps an unauthenticated flood from
+// choosing how much session work the process does.
+//
+// What that ordering costs: the 413 branch is reachable
+// unauthenticated, at a URL of the client's choosing and of the
+// client's chosen length. So is the CSRF rejection, which sits in
+// front of RequireAuth for the same reason. Both log that path, so
+// both cap it — see the log calls in Middleware.MaxBodySize and
+// Middleware.CSRF, which spend the same per-field budget as the
+// access log.
 const maxFormBodySize int64 = 1 * 1024 * 1024 // 1 MB

 // requestTimeout is the maximum time allowed for a single HTTP
@@ -90,8 +112,8 @@ func (s *Server) setupRoutes() {

 func (s *Server) setupPageRoutes() {
 	s.router.Route("/pages", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
+		// MaxBodySize precedes CSRF and RequireAuth deliberately;
+		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
@@ -111,8 +133,8 @@ func (s *Server) setupPageRoutes() {

 func (s *Server) setupUserRoutes() {
 	s.router.Route("/user/{username}", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
+		// MaxBodySize precedes CSRF and RequireAuth deliberately;
+		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
@@ -126,8 +148,8 @@ func (s *Server) setupUserRoutes() {

 func (s *Server) setupSourceRoutes() {
 	s.router.Route("/sources", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
+		// MaxBodySize precedes CSRF and RequireAuth deliberately;
+		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
@@ -138,8 +160,8 @@ func (s *Server) setupSourceRoutes() {
 	})

 	s.router.Route("/source/{sourceID}", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
+		// MaxBodySize precedes CSRF and RequireAuth deliberately;
+		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
Author	SHA1	Message	Date
clawbot	04678d07e3	Route GORM's logger through slog and bound it (closes #178 ) All checks were successful check / check (push) Successful in 3m31s Details GORM's default logger printed the fully interpolated SQL to standard output on every statement that returned an error, including a plain record-not-found. On /webhook/{uuid} and on the login form the interpolated parameter is client-chosen and unbounded, so an unauthenticated client sized the operator's log, one line per request, at no level the operator could turn down. Every gorm.Open in the service now installs internal/gormlog, a gormlogger.Interface over the service's *slog.Logger. Its lines take the level the operator set and the handler internal/logger selected; a record-not-found is not logged as an error, since it is the expected outcome on both of those paths and each handler already records its own miss at DEBUG without the SQL; slow statements are kept at WARN above the same 200ms threshold GORM used; and every value it emits is spent through internal/logfield, the same encoded-byte budget the access log spends. MaxAccessLogLineBytes bounds a GORM line too, and internal/gormlog asserts each line against the constant directly. Trace orders its cases exactly as GORM's own Trace orders them -- error-that-is-not-a-miss, then slow, then routine -- so a statement that both missed and ran slow is still reported as slow. Ordering the drop first would have made this adapter strictly less observant than the IgnoreRecordNotFoundError option it was chosen over, on the two lookups the issue is about, and a miss is the statement most likely to be slow. The third gorm.Open, in the archive writer, was not named in the issue and had the same default. All three sites are pinned independently: internal/handlers covers the main and per-webhook databases, internal/delivery covers the archive writer, whose type is unexported. Reverting any one of the three to a bare &gorm.Config{} fails the suite. The flood test's per-line and volume assertions were vacuous, because the replaced default logger wrote only to a buffer while everything else went to the captured stdout. It now tees to stdout as GORM's real default does, so a reverted call site lands in the same capture and those assertions measure the whole writer set. internal/logfield gains the zero-headroom budget assertion and the rune-splitting case: a value built from one rune must keep exactly MaxBytes/EncodedBytes(r) of them, which a raw-byte budget fails and a LessOrEqual on the budget cannot catch. README: the ceiling now covers GORM, and the writers it does not cover are re-derived by measuring rather than by reading. fx's console logger and the Go runtime write to standard error. net/http's nil ErrorLog is not a separate writer at all -- slog.SetDefault redirects the log package's default logger into internal/logger's handler, so those lines arrive on standard output at INFO. A handler panic reaches that same path because chi's Recoverer crashes before writing, filed as #187, and is the widest line the service can write: measured at roughly 2,770 bytes against the stated 2,560, a width that moves with the goroutine number and the source paths in the stack, so only the fact that it exceeds the ceiling is stated as invariant.	2026-08-18 04:18:36 +00:00
clawbot	563e834cf2	Bound every slog line against client-chosen text (closes #176 ) All checks were successful check / check (push) Successful in 2m55s Details	2026-08-18 06:03:10 +02:00
clawbot	f6ec78e2c8	Stop a slow host turning a login-guard test into a segfault (closes #186 ) All checks were successful check / check (push) Successful in 2m49s Details	2026-08-18 05:01:13 +02:00
clawbot	9313b0fb41	Merge pull request 'Correct TODO.md milestone state and record seventeen landed units' (#192 ) from todo-md-milestone-state into next All checks were successful check / check (push) Successful in 6s Details	2026-08-18 04:07:39 +02:00
clawbot	d2cebb5783	Correct TODO.md milestone state and record seventeen landed units All checks were successful check / check (push) Successful in 6s Details The Status section claimed next held the completed 1.0.0 milestone with every issue closed. Four are open (#176, #178, #186, #187), so a merge of next to main would have shipped that claim to main. Next Step still named #115 and #125 as open owner decisions; both landed. It now names the real open items, #150 and #112, and the forced merge order for the remaining four. Completed Steps was seventeen units behind, back to 2026-08-12.	2026-08-18 02:06:43 +00:00