Log SQL with placeholders, never bound values (closes #207) (#222)

README.md

@@ -256,6 +256,51 @@ On first startup, webhooker creates an `admin` user
 with a randomly generated password and logs it to stdout. This password
 is only displayed once.
 
+#### What `DEBUG=true` exposes
+
+`DEBUG=true` lowers the log level to `DEBUG`, which turns on every
+statement GORM runs, the two by-design lookup misses on the
+unauthenticated routes, and the rate limiter's own rejections. It is
+meant to be safe to turn on while diagnosing a live service and safe to
+paste the output of into a bug report.
+
+What it does **not** put in the log:
+
+- **Values bound to a SQL statement.** Statements are logged with their
+  placeholders, never with the values substituted into them, at every
+  level. That is what keeps the session encryption key out of the first
+  boot's `INSERT INTO settings` and the `admin` account's Argon2id
+  password hash out of its `INSERT INTO users` — the two statements
+  that made a debug log worth stealing. It applies to every table and
+  every statement rather than to a list of tables known to hold a
+  secret, so a table added later is covered without anyone remembering
+  to add it. The cost is that a failing statement can no longer be
+  replayed from the log alone: the statement, the table, the driver
+  error and the row count are all still there, but its values have to
+  come from the database.
+  `internal/gormlog/firstboot_test.go` boots the real graph with
+  `DEBUG=true` against an empty `DATA_DIR` and asserts that neither
+  secret appears in what that boot wrote to stdout.
+  The one exception is `(*gorm.DB).Scan`, which GORM logs through its
+  own trace recorder rather than through this filter. No production
+  code path calls it, and `internal/gormlog/scan_guard_test.go` fails
+  if a non-test file adds one.
+- **Session cookies, API keys or target credentials.** None of these is
+  logged at any level.
+
+What is in the log regardless of `DEBUG`, and is not a debug-logging
+decision:
+
+- **The initial `admin` password**, in the clear, once, at `INFO`, on
+  the first boot that creates the account. That line is the only place
+  it is ever shown; the database stores the hash. A first boot's output
+  is not safe to paste anywhere until that account's password has been
+  changed.
+- **An authenticated operator's own configuration**, echoed back
+  untruncated — webhook names, target hostnames. See the logging
+  section under Security for the full list and for the per-line size
+  bound that covers unauthenticated traffic.
+
 ### Running with Docker
 
 ```bash
@@ -1464,6 +1509,24 @@ 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.
 
+The adapter also logs no bound value at all: it implements
+`gorm.ParamsFilter` and discards the parameters, so GORM renders the
+statement with its placeholders intact instead of substituting the
+values into it. That is a separate property from the size bound and it
+is what a bound is no substitute for — the session encryption key is 44
+base64 characters and an Argon2id hash under 100, so both fit inside
+every budget above and a truncated secret is still a secret. It holds
+on all three arms of `Trace`, including the routine one an operator
+reaches at `DEBUG`, which is the only level at which a successful
+`INSERT` is written at all. One GORM path does not consult the filter —
+`(*gorm.DB).Scan`, which records the statement through GORM's own trace
+recorder. No production code path calls it; its one caller is
+`internal/database/database_test.go:91`, whose `SELECT 1` binds
+nothing, and `internal/gormlog/scan_guard_test.go` fails if a non-test
+file calls it. `Pluck`, `Row` and `Raw` all run through the normal
+callback processor and are filtered.
+See `#### What DEBUG=true exposes` under Configuration.
+
 What that ceiling does **not** cover, stated here so the figure is not
 read as more than it is: