[zpyoung]

	Files	Added	Deleted	Net
Test	0	0	0	0
Prod	1	$\color{#1a7f37}{\Huge{\mathbf{+}}}$​36	$\color{#cf222e}{\Huge{\mathbf{−}}}$​2	$\color{#1a7f37}{\Huge{\mathbf{+}}}$​34

Two lessons from the v1.4.206 re-cut sync (#87). Both are rules, so both are edited into the step
that owns them — references/file-ownership.md. Nothing here touches SKILL.md or
sync-lessons.md, so it cannot conflict with #85 or #86.

1. The locale sweep pointed at a directory that does not exist

The reference told the run to sweep fork locale bundles against src/renderer/src/locales/*.json.
That directory does not exist — not at v1.4.206, and not at the previous tag either:

$ git ls-tree -r --name-only c464b10149 -- src/renderer/src/locales   # (retracted v1.4.206)
$ git ls-tree -r --name-only c62eca3988 -- src/renderer/src/locales   # (re-cut v1.4.206)
$ git ls-tree -r --name-only HEAD       -- src/renderer/src/i18n/locales | head -3
src/renderer/src/i18n/locales/en.json
src/renderer/src/i18n/locales/es.json
src/renderer/src/i18n/locales/fr.json

Run as documented with ls, the sweep errors. Run the way an agent will naturally reach for —
a Python glob or find — it returns the empty set, and every fork bundle then compares clean
against zero required locales:

upstream locales: []
(fork bundles with missing locales: 0)

That is the false-pass shape this reference warns about elsewhere, and it reported success on the
one check that exists to catch a missing locale file. Re-run against the real directory, the
answer was also zero — but only by luck.

The fix corrects the path in both places and adds the rule: resolve the directory, and confirm the
locale set is non-empty before trusting the comparison. The path has moved once, so it can move
again; a pasted path fails silent while a resolved one fails loud.

2. A fork seam threw inside upstream's own test fixture

v1.4.206 added pending-split-close-test-fixture.ts. It is upstream's fixture, built for
upstream's code, and it supplies no settingsRef. The terminal-dock seam in
terminal-pane-pane-closed.ts read:

deps.settingsRef.current?.experimentalTerminalDock === true,

Optional on .current, but not on the ref. Three of upstream's pending-close suites threw
TypeError: Cannot read properties of undefined (reading 'current') across shards 4, 5 and 6 —
one fork line failing suites the fork has no stake in, in files it does not own.

Nothing in the ownership pass sees this. --verify-seams passes (the declared line is present),
--verify-residuals passes, the guard passes, and all four typecheck projects pass. It appears
only in PR CI, and the stack reads as a renderer bug rather than a seam question.

The skill had no guidance for this at all — the only record was a note outside the repo. The new
section gives the tell (a TypeError whose stack runs upstream test → upstream fixture → one fork
line in an upstream file), the rule (optional-chain the whole access path, absent state means the
feature is off, open durable state lazily), and why the guard belongs in the seam rather than in
the fixture: upstream's fixture resets to the tag every sync, so hardening it there is undone at
the next release.

Fixed in #87 as 98ca77ac0d.