Suppress the startup banner for --json (closes #106)

The banner is printed to stdout before cobra parses, and
bannerSuppressedInArgs recognised only --quiet, -q and --cron. So every
--json document was preceded by two banner lines and a blank one, and
`vaultik snapshot list --json | jq` failed. Passing opts.JSON as
extraQuiet did not help: that calls UI.SetQuiet in an fx OnStart hook,
long after Entry has printed.

The raw-argv scan is extended rather than the banner moved after
parsing. root.go documents that the banner must survive cobra rejecting
its arguments and --help, and no single post-parse location covers those
paths. The subcommand-versus-persistent distinction does not decide it:
--cron is already in the suppression list and is itself subcommand-only,
existing on snapshot create alone, so this adds another instance of an
accepted imprecision rather than a new kind. The error directions are
asymmetric - a false positive loses a decorative banner, a false negative
corrupts a document - so the scan errs toward suppression, which is also
why --json=false suppresses, exactly as --quiet=false already does.

Four of the five --json commands now pipe into jq cleanly with no other
flags: snapshot list, snapshot verify, snapshot remove, remote info.
prune does not, because pruneLocalSnapshots writes three prose lines to
stdout with no --json awareness. That reproduces identically before this
change and -q never suppressed it either, since printlnStdout and
stdoutf bypass v.UI entirely. Tracked as #108.

Also fixed: TTYHandler's human-readable byte formatting did not survive
grouping, because the key check compared against the bare attribute name
and a grouped record presents it qualified. AGENTS.md policy 9 keyed the
log format on stdout's TTY-ness, which #82 made false by moving the
logger to stderr; it now names the log stream. Vaultik.Stderr keeps its
field with the comment amended to say outright that nothing writes to
it, and the dead listEnv.stderr is removed.

AGENTS.md

@@ -83,8 +83,8 @@ Version: 2025-06-08
    possible to mock or stub these side-effects in tests.
 
 9. Always use structured logging.  Log any relevant state/context with the
-   messages (but do not log secrets).  If stdout is not a terminal, output
-   the structured logs in jsonl format.
+   messages (but do not log secrets).  If the log stream is not a terminal,
+   output the structured logs in jsonl format.
 
 10. Avoid using bare strings or numbers in code, especially if they appear
     anywhere more than once.  Always define a constant (usually at the top

README.md

@@ -139,6 +139,11 @@ Format follows the stream: when stderr is a terminal the records are
 colorized one-liners, and when it is redirected or piped they are
 JSON, one object per line.
 
+The startup banner is the other thing that writes to stdout, and
+`--json` suppresses it, as `--quiet` and `--cron` do. So
+`vaultik snapshot list --json | jq .` works on its own, with no
+additional flag to quiet the banner first.
+
 ### environment variables
 
 * `VAULTIK_AGE_SECRET_KEY`: Age private key for decryption (required for `snapshot restore` and `snapshot verify --deep`)

TODO.md

@@ -25,6 +25,44 @@ release" is exactly the contradiction
 
 # Completed Steps
 
+- 2026-08-09: Stopped the startup banner from contaminating `--json`
+  documents ([issue #106](https://git.eeqj.de/sneak/vaultik/issues/106)).
+  `Entry` writes the banner to stdout before cobra parses anything, and
+  the flag scan that suppresses it knew `--quiet`, `-q` and `--cron` but
+  not `--json`, so every `--json` document arrived behind two lines of
+  prose and a blank line, and `vaultik snapshot list --json | jq` failed.
+  With the logger already on stderr from
+  [issue #82](https://git.eeqj.de/sneak/vaultik/issues/82), this was the
+  last writer that could put something on stdout that the caller did not
+  ask for. The design question the issue raised — extend the raw-argv
+  scan, or move the banner after parsing — is answered in favour of the
+  scan: the banner is printed first deliberately, so that it still
+  appears when cobra rejects the arguments and on `--help`, and after
+  parsing there is no single place that covers those paths. The stated
+  cost of the scan, that `--json` is a subcommand flag matched anywhere
+  in the vector, is a cost `--cron` already carries — it exists only on
+  `snapshot create` — so this adds an instance of an accepted
+  imprecision rather than a new kind, and the two error directions are
+  not symmetric: a false positive loses a decorative banner, a false
+  negative corrupts a document. Regression tests at the CLI layer, where
+  `internal/vaultik`'s existing guard cannot reach: one runs `Entry`
+  itself over the process's real stdout descriptor, through cobra and fx
+  to the document, made hermetic by `file://` storage; a second covers
+  the argument vectors of all five `--json` commands; a third asserts the
+  banner is still printed without a suppressing flag, so the first
+  cannot be satisfied by deleting the banner. Also corrected `AGENTS.md`
+  policy 9, which still keyed the structured-log format on stdout's
+  TTY-ness after #82 moved that decision to stderr — a rules file that
+  misdescribes the code misleads exactly the readers who trust it most.
+  Two smaller findings from the same review: `bytesAttrKey`'s
+  human-readable byte formatting silently stopped applying under an open
+  group, because the key reaching the comparison is group-qualified
+  (`transfer.bytes`), now matched on its final segment and tested both
+  ways; and `listEnv.stderr` in `snapshot_list_test.go`, assigned but
+  never read since those tests began capturing the process's stderr, is
+  removed. `Vaultik.Stderr` is kept — nothing writes to it today, which
+  its comment now says outright.
+
 - 2026-08-09: Moved the logger to stderr and fixed `TTYHandler`'s
   discarded attributes
   ([issue #82](https://git.eeqj.de/sneak/vaultik/issues/82),

internal/cli/entry.go

@@ -1,6 +1,7 @@
 package cli
 
 import (
+	"io"
 	"os"
 	"strings"
 	"time"
@@ -14,18 +15,12 @@ import (
 const shortCommitLen = 12
 
 // Entry is the main entry point for the CLI application.
-// It prints the startup banner (unless a quiet flag is present in os.Args),
-// executes the root cobra command, and routes any returned error through
-// the ui.Writer so the user sees a properly formatted "🛑 ERROR:" line.
+// It prints the startup banner to stdout (unless a banner-suppressing
+// flag is present in os.Args — see bannerSuppressedInArgs), executes the
+// root cobra command, and routes any returned error through the
+// ui.Writer so the user sees a properly formatted "🛑 ERROR:" line.
 func Entry() {
-	if !bannerSuppressedInArgs(os.Args[1:]) {
-		short := globals.Commit
-		if len(short) > shortCommitLen {
-			short = short[:shortCommitLen]
-		}
-
-		writeStartupBanner(ui.New(os.Stdout), time.Now().UTC(), short)
-	}
+	emitStartupBanner(os.Args[1:], os.Stdout)
 
 	rootCmd := NewRootCommand()
 	rootCmd.SilenceErrors = true
@@ -37,6 +32,24 @@ func Entry() {
 	}
 }
 
+// emitStartupBanner writes the startup banner to w unless args (the
+// argument vector with the program name already stripped) contains a
+// flag that suppresses it. Split out of Entry so that the decision — the
+// only thing standing between a --json invocation and a parseable
+// stdout — is reachable from a test without running the whole CLI.
+func emitStartupBanner(args []string, w io.Writer) {
+	if bannerSuppressedInArgs(args) {
+		return
+	}
+
+	short := globals.Commit
+	if len(short) > shortCommitLen {
+		short = short[:shortCommitLen]
+	}
+
+	writeStartupBanner(ui.New(w), time.Now().UTC(), short)
+}
+
 // ReportErrorf emits a user-facing error to stderr in the standard
 // 🛑 ERROR: format. Use it from goroutine error paths (where returning
 // an error to cobra isn't an option) and anywhere else a CLI command
@@ -46,9 +59,20 @@ func ReportErrorf(format string, args ...any) {
 }
 
 // bannerSuppressedInArgs reports whether any of args is a flag that
-// should suppress the startup banner (--quiet/-q/--cron). Stops at the
-// "--" argument terminator. Recognizes both long forms and short -q,
-// including combined short flags like "-qv".
+// should suppress the startup banner (--quiet/-q/--cron/--json). Stops
+// at the "--" argument terminator. Recognizes both long forms and short
+// -q, including combined short flags like "-qv".
+//
+// This scans the raw argument vector because the banner is printed
+// before cobra parses anything — deliberately, so that it still appears
+// when cobra rejects the arguments and on --help. The consequence is
+// that a flag is matched wherever it occurs in the vector, including
+// positions where the command it belongs to would not accept it.
+// --json is a subcommand flag rather than a persistent one, but so is
+// --cron (it exists only on `snapshot create`), so this adds no new
+// class of imprecision. The only cost of a false positive is a missing
+// decorative banner; the cost of a false negative is a corrupt document
+// on stdout, so the scan errs deliberately in that direction.
 func bannerSuppressedInArgs(args []string) bool {
 	for _, a := range args {
 		if a == "--" {
@@ -56,11 +80,13 @@ func bannerSuppressedInArgs(args []string) bool {
 		}
 
 		switch a {
-		case "--quiet", "-q", "--cron":
+		case "--quiet", "-q", "--cron", "--json":
 			return true
 		}
 
-		if strings.HasPrefix(a, "--quiet=") || strings.HasPrefix(a, "--cron=") {
+		if strings.HasPrefix(a, "--quiet=") ||
+			strings.HasPrefix(a, "--cron=") ||
+			strings.HasPrefix(a, "--json=") {
 			return true
 		}
 		// Combined short flags like -qv or -vq.

internal/cli/entry_banner_test.go

@@ -0,0 +1,295 @@
+package cli //nolint:testpackage // needs access to unexported emitStartupBanner
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/adrg/xdg"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// Command words and flags used to build argument vectors below. They are
+// constants rather than repeated literals so that a rename shows up as a
+// compile error in one place.
+const (
+	cmdSnapshot = "snapshot"
+	cmdList     = "list"
+	cmdCreate   = "create"
+	cmdVerify   = "verify"
+	cmdRemove   = "remove"
+	cmdPrune    = "prune"
+	cmdRemote   = "remote"
+	cmdInfo     = "info"
+
+	flagJSON  = "--json"
+	flagQuiet = "--quiet"
+
+	// someSnapshotID is any snapshot identifier: these tests never run
+	// the command, so it only has to occupy the positional argument.
+	someSnapshotID = "host_2026-01-01T00:00:00Z"
+)
+
+// placeholderJSONDocument stands in for whatever document a --json
+// command writes to stdout. `snapshot list --json` with no snapshots
+// prints exactly this; the other --json commands print an object rather
+// than an array, but this test is not about their shape. It is about
+// what is on stdout *before* them, which is the same for all of them
+// because Entry prints the banner before cobra has parsed anything and
+// therefore before it can know which command is running.
+const placeholderJSONDocument = "[]\n"
+
+// jsonArgumentVectors are the argument vectors of every --json
+// invocation the CLI accepts, with the program name stripped exactly as
+// Entry strips it. Each one must leave stdout untouched by the banner.
+//
+//nolint:gochecknoglobals // read-only test fixture shared by two tests
+var jsonArgumentVectors = map[string][]string{
+	"snapshot list":   {cmdSnapshot, cmdList, flagJSON},
+	"snapshot verify": {cmdSnapshot, cmdVerify, someSnapshotID, flagJSON},
+	"snapshot remove": {cmdSnapshot, cmdRemove, someSnapshotID, flagJSON},
+	"prune":           {cmdPrune, flagJSON},
+	"remote info":     {cmdRemote, cmdInfo, flagJSON},
+
+	// --json before the subcommand, and with an explicit value: the
+	// scan is positional, so both forms have to be recognized.
+	"json first":      {flagJSON, cmdSnapshot, cmdList},
+	"json with value": {cmdSnapshot, cmdList, flagJSON + "=true"},
+
+	// A --json invocation that also carries a flag with a value, so the
+	// scan cannot be fooled by an argument that consumes the next one.
+	"json with config": {
+		"--config", "/nonexistent/vaultik.yml", cmdSnapshot, cmdList, flagJSON,
+	},
+}
+
+// TestJSONInvocationStdoutIsExactlyOneDocument is the CLI-layer
+// regression guard for issue #106: `vaultik snapshot list --json | jq`
+// must work with no other flags.
+//
+// internal/vaultik's TestListSnapshots_JSONStdoutIsOnlyTheDocument
+// guards the same contract one layer down, but it calls the library
+// function directly and so cannot see Entry, which is where the
+// contamination was: the startup banner is written to stdout before
+// cobra parses anything, and the suppression scan did not know about
+// --json. The two banner lines and the blank line landed ahead of the
+// document and `jq` refused the result.
+//
+// The document is a constant here because this test is about the
+// argument vectors, one per --json command; the one that runs a real
+// command end to end is TestEntryJSONStdoutIsExactlyOneDocument below.
+func TestJSONInvocationStdoutIsExactlyOneDocument(t *testing.T) {
+	t.Parallel()
+
+	for name, argv := range jsonArgumentVectors {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			var stdout bytes.Buffer
+
+			emitStartupBanner(argv, &stdout)
+
+			require.Empty(t, stdout.String(),
+				"nothing may reach stdout ahead of a --json document")
+
+			_, err := stdout.WriteString(placeholderJSONDocument)
+			require.NoError(t, err)
+
+			requireExactlyOneJSONDocument(t, stdout.String())
+		})
+	}
+}
+
+// TestBannerStillPrintedWithoutSuppressingFlag pins the other half of
+// the contract. Without it, deleting the banner outright would satisfy
+// the test above, and the banner is wanted on interactive invocations.
+func TestBannerStillPrintedWithoutSuppressingFlag(t *testing.T) {
+	t.Parallel()
+
+	for name, argv := range map[string][]string{
+		"no flags": {cmdSnapshot, cmdList},
+		"verbose":  {cmdSnapshot, cmdList, "--verbose"},
+		"after the terminator": {
+			cmdSnapshot, "restore", "--", flagJSON,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			var stdout bytes.Buffer
+
+			emitStartupBanner(argv, &stdout)
+
+			assert.Contains(t, stdout.String(), "starting up at",
+				"the banner belongs on invocations that did not opt out")
+		})
+	}
+}
+
+// TestBannerSuppressedInArgs covers the suppression scan directly,
+// including the flags that suppressed the banner before --json joined
+// them, so that adding --json cannot regress them.
+func TestBannerSuppressedInArgs(t *testing.T) {
+	t.Parallel()
+
+	for name, testCase := range map[string]struct {
+		args       []string
+		suppressed bool
+	}{
+		"quiet long":     {[]string{cmdSnapshot, cmdCreate, flagQuiet}, true},
+		"quiet short":    {[]string{cmdSnapshot, cmdCreate, "-q"}, true},
+		"quiet combined": {[]string{cmdSnapshot, cmdCreate, "-qv"}, true},
+		"cron":           {[]string{cmdSnapshot, cmdCreate, "--cron"}, true},
+		"json":           {[]string{cmdSnapshot, cmdList, flagJSON}, true},
+		"nothing":        {[]string{cmdSnapshot, cmdList}, false},
+		"empty":          {nil, false},
+		"json after dashes": {
+			[]string{cmdSnapshot, cmdList, "--", flagJSON}, false,
+		},
+		"quiet after dashes": {
+			[]string{cmdSnapshot, cmdCreate, "--", "-q"}, false,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			assert.Equal(t, testCase.suppressed,
+				bannerSuppressedInArgs(testCase.args))
+		})
+	}
+}
+
+// hermeticConfig is a complete, valid config that needs no network and
+// no credentials: file:// storage is exempt from the S3 credential
+// checks, and FileStorer over a directory that does not exist lists
+// zero objects without erroring. Chunk, blob and compression settings
+// are filled in by config.Load.
+const hermeticConfig = `age_recipients:
+  - age1278m9q7dp3chsh2dcy82qk27v047zywyvtxwnj4cvt0z65jw6a7q5dqhfj
+snapshots:
+  test:
+    paths:
+      - %s
+storage_url: file://%s
+index_path: %s
+hostname: test-host
+`
+
+// TestEntryJSONStdoutIsExactlyOneDocument runs the real thing: Entry,
+// with a real argument vector, over the process's real stdout file
+// descriptor, all the way through cobra and the fx graph to the
+// document. It is the assertion the issue asks for — `vaultik snapshot
+// list --json | jq .` with no other flags — with the pipe replaced by a
+// decoder.
+//
+// `snapshot list` is the command chosen because it is the only --json
+// command that reaches its document without a populated destination
+// store: it reads the local index, streams `metadata/` (empty here),
+// and treats a barren destination as an empty list rather than a
+// failure.
+//
+// Not parallel: it replaces os.Args, os.Stdout and the xdg globals.
+func TestEntryJSONStdoutIsExactlyOneDocument(t *testing.T) {
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.yml")
+
+	contents := fmt.Sprintf(hermeticConfig,
+		filepath.Join(dir, "source"),
+		filepath.Join(dir, "store"),
+		filepath.Join(dir, "index.sqlite"))
+
+	require.NoError(t,
+		os.WriteFile(configPath, []byte(contents), configFileMode))
+
+	// The PID lock lives under xdg.DataHome, which xdg resolves at
+	// package init; point it at the temp dir so the test neither
+	// touches nor collides with the real one.
+	t.Setenv("XDG_DATA_HOME", filepath.Join(dir, "data"))
+	xdg.Reload()
+	t.Cleanup(xdg.Reload)
+
+	previousArgs := os.Args
+
+	t.Cleanup(func() {
+		os.Args = previousArgs
+		rootFlags = RootFlags{}
+	})
+
+	os.Args = []string{
+		"vaultik", "--config", configPath, cmdSnapshot, cmdList, flagJSON,
+	}
+
+	stdout := captureProcessStdout(t, Entry)
+
+	requireExactlyOneJSONDocument(t, stdout)
+
+	var snapshots []any
+
+	require.NoError(t, json.Unmarshal([]byte(stdout), &snapshots))
+	assert.Empty(t, snapshots,
+		"a destination store with no snapshots lists none")
+}
+
+// captureProcessStdout redirects the process's own stdout to a pipe for
+// the duration of fn and returns what was written to it. The redirection
+// has to be at the file-descriptor level rather than through an injected
+// writer, because the banner and the JSON encoder reach os.Stdout
+// independently and the point of the test is that both land in the same
+// place.
+//
+// Not parallel-safe: os.Stdout is process-global.
+func captureProcessStdout(t *testing.T, fn func()) string {
+	t.Helper()
+
+	reader, writer, err := os.Pipe()
+	require.NoError(t, err)
+
+	previous := os.Stdout
+	os.Stdout = writer
+
+	captured := make(chan string, 1)
+
+	go func() {
+		var buf bytes.Buffer
+
+		_, _ = io.Copy(&buf, reader)
+		captured <- buf.String()
+	}()
+
+	fn()
+
+	os.Stdout = previous
+
+	require.NoError(t, writer.Close())
+
+	out := <-captured
+
+	require.NoError(t, reader.Close())
+
+	return out
+}
+
+// requireExactlyOneJSONDocument fails unless stdout decodes as a single
+// JSON value with nothing before or after it — the property that makes
+// `| jq` work.
+func requireExactlyOneJSONDocument(t *testing.T, stdout string) {
+	t.Helper()
+
+	decoder := json.NewDecoder(strings.NewReader(stdout))
+
+	var document any
+
+	err := decoder.Decode(&document)
+	require.NoError(t, err,
+		"stdout must parse as JSON, got:\n%s", stdout)
+
+	_, err = decoder.Token()
+	require.ErrorIs(t, err, io.EOF,
+		"stdout must hold exactly one JSON document, got:\n%s", stdout)
+}

internal/log/tty_handler.go

@@ -16,9 +16,23 @@ import (
 const groupSeparator = "."
 
 // bytesAttrKey is the attribute key whose int64 value is rendered as a
-// human-readable byte count rather than a bare number.
+// human-readable byte count rather than a bare number. Keys reaching
+// writeAttr are group-qualified, so the match is made against the final
+// dot-separated segment: without that, a "bytes" attribute logged under
+// an open group would arrive as "transfer.bytes" and silently lose its
+// formatting.
 const bytesAttrKey = "bytes"
 
+// isBytesAttr reports whether a group-qualified attribute key names the
+// byte-count attribute, i.e. whether its last segment is bytesAttrKey.
+func isBytesAttr(key string) bool {
+	if idx := strings.LastIndex(key, groupSeparator); idx >= 0 {
+		key = key[idx+len(groupSeparator):]
+	}
+
+	return key == bytesAttrKey
+}
+
 // ANSI color codes
 const (
 	colorReset  = "\033[0m"
@@ -236,7 +250,7 @@ func (h *TTYHandler) writeAttr(a slog.Attr) {
 			value = formatDuration(d)
 		}
 	case slog.KindInt64:
-		if a.Key == bytesAttrKey {
+		if isBytesAttr(a.Key) {
 			value = formatBytes(a.Value.Int64())
 		}
 	case slog.KindAny, slog.KindBool, slog.KindFloat64, slog.KindString,

internal/log/tty_handler_test.go

@@ -190,6 +190,51 @@ func TestTTYHandlerWithGroupQualifiesKeys(t *testing.T) {
 	assert.NotContains(t, attrs, "rows")
 }
 
+// TestTTYHandlerByteFormattingSurvivesGrouping guards the interaction
+// between the two features. The human-readable rendering of a "bytes"
+// attribute is selected by comparing the key, and keys reaching that
+// comparison are group-qualified, so a "bytes" attribute logged under an
+// open group arrived as "transfer.bytes" and fell back to a bare number.
+// No caller groups a byte count today, which is exactly why this needs a
+// test rather than a bug report.
+func TestTTYHandlerByteFormattingSurvivesGrouping(t *testing.T) {
+	t.Parallel()
+
+	const oneAndAHalfKiB = 1536
+
+	for name, testCase := range map[string]struct {
+		derive func(*slog.Logger) *slog.Logger
+		key    string
+	}{
+		"ungrouped": {
+			derive: func(l *slog.Logger) *slog.Logger { return l },
+			key:    "bytes",
+		},
+		"grouped": {
+			derive: func(l *slog.Logger) *slog.Logger {
+				return l.WithGroup("transfer")
+			},
+			key: "transfer.bytes",
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			var buf bytes.Buffer
+
+			logger := slog.New(log.NewTTYHandler(&buf, debugHandlerOptions()))
+			testCase.derive(logger).Info("uploaded", "bytes", oneAndAHalfKiB)
+
+			line := ansiEscape.ReplaceAllString(buf.String(), "")
+
+			assert.Contains(t, line, testCase.key+"=1.5 KB",
+				"a byte count must be human-readable however it is qualified")
+			assert.NotContains(t, line, strconv.Itoa(oneAndAHalfKiB),
+				"the raw number must not survive the formatting")
+		})
+	}
+}
+
 // TestTTYHandlerMatchesJSONHandlerAttributes is the drift guard. The
 // handler is chosen by TTY-ness, so a difference between these two is
 // invisible in whichever environment the developer is not in — which is

internal/vaultik/snapshot_list_test.go

@@ -108,7 +108,6 @@ type listEnv struct {
 	v      *vaultik.Vaultik
 	store  *observingStorer
 	stdout *bytes.Buffer
-	stderr *bytes.Buffer
 }
 
 func newListEnv(t *testing.T) *listEnv {
@@ -122,7 +121,6 @@ func newListEnv(t *testing.T) *listEnv {
 
 	store := newObservingStorer()
 	stdout := &bytes.Buffer{}
-	stderr := &bytes.Buffer{}
 
 	v := &vaultik.Vaultik{
 		Config: &config.Config{
@@ -135,13 +133,13 @@ func newListEnv(t *testing.T) *listEnv {
 		Repositories: database.NewRepositories(db),
 		DB:           db,
 		Stdout:       stdout,
-		Stderr:       stderr,
+		Stderr:       &bytes.Buffer{},
 		Stdin:        &bytes.Buffer{},
 		UI:           ui.NewWithColor(stdout, false),
 	}
 	v.SetContext(ctx)
 
-	return &listEnv{v: v, store: store, stdout: stdout, stderr: stderr}
+	return &listEnv{v: v, store: store, stdout: stdout}
 }
 
 // addLocal inserts a completed snapshot into the local index.

internal/vaultik/vaultik.go

@@ -47,7 +47,11 @@ type Vaultik struct {
 	// so that `--json | jq` works. Stderr completes the standard triple
 	// for anything a command needs to write there directly; diagnostics
 	// are not that — they go through internal/log, which writes to the
-	// process's stderr.
+	// process's stderr. No production code writes to Stderr today, so
+	// searching for its writers turns up nothing; it is kept as the
+	// injection point a direct stderr write would otherwise have to
+	// invent, and removing it would make the triple asymmetric for no
+	// gain.
 	Stdout io.Writer
 	Stderr io.Writer
 	Stdin  io.Reader