docs(#2674): amend ADR-1411 — corrupt is not absent (epic #1879 Phase 0) (#2678)

* docs(#2674): amend adr-1411 with the corrupt-is-not-absent house pattern

ADR-1411 reasons only about a resolution miss. It is silent on input that
is present but not usable, which is how five engine read paths (#1879) could
fold an unusable input into the value meaning 'genuinely absent' without
contradicting an Accepted ADR.

Read together, ADR-1411 and ADR-227 converge and do not license throwing as
the cluster's answer: ADR-227 requires malformed input to be coerced rather
than propagated and carves out only genuinely-fatal fields, while ADR-1411
already permits a fallback provided it is 'a visible value, not a silent
substitution'. The defect in these five sites is therefore not that they fall
back but that they fall back invisibly.

Records the pattern that follows: every current return value is preserved, and
the cause is made visible in-band where the result already carries a
provenance envelope, or out-of-band via a deduplicated stderr diagnostic where
it returns a bare value it cannot extend. Throwing stays confined to ADR-227's
genuinely-fatal carve-out, decided per call. Also names the per-applier caller
audit and the lint-resolution-provenance registry gap.

Refs #1879

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* test(#2674): prove the warning-state reset misses the unknown-key dedup set

The two existing cases in this suite only pass because each picks a key
name no other case reuses, so neither can observe whether the reset the
beforeEach calls actually runs.

Failing-first: asserts the exported _warnedUnknownConfigKeys is empty after
_resetRuntimeWarningCacheForTests(). It is not - the helper clears only
_warnedConfigKeys despite documenting itself as resetting per-process
warning state.

Refs #1879

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* fix(#2674): reset the unknown-key dedup set with the runtime warning cache

_resetRuntimeWarningCacheForTests documents itself as resetting per-process
warning state but cleared only _warnedConfigKeys, leaving
_warnedUnknownConfigKeys populated across cases. The suite that exists to
test that set - 'loadConfig - unknown-key warning dedup' - calls the helper
in beforeEach expecting exactly this, so the reset was a silent no-op for
it; both cases passed only because each picked a key name the other never
reused. Any later case reusing a key would have had its warning suppressed
by leaked state.

Found while amending ADR-1411, which names this dedup guard as the pattern
five downstream PRs (#1880-#1884) will adopt - shipping the ADR without the
fix would have propagated the footgun to each of them. Folded in here per
CLAUDE.md's no-defer rule rather than filed.

RED verified on 3c4895841 (test only, no fix): linux-node22 reported
'FAIL tests/config-loader.test.cjs - the documented per-process
warning-state reset must clear the unknown-key dedup set too'.

Refs #1879

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* docs(#2674): document src/ in the changeset-lint trigger list

CONTRIBUTING.md presented the Changeset Required trigger list as bin/,
gsd-core/, agents/, commands/, hooks/, sdk/src/ - omitting src/, which
scripts/changeset/lint.cjs has in USER_FACING_PREFIXES. src/ is the
TypeScript source of truth compiled into gsd-core/bin/lib/*.cjs, so it is
the most-edited user-facing path in the repo and the omission sends any
contributor who touches it into a CI failure the doc says cannot happen.

Also documents that the lint reads GITHUB_BASE_REF, which only CI sets, so
running it bare locally reports success without evaluating the branch. This
PR hit exactly that: a local run said ok_fragment_present and CI failed
fail_missing_fragment on the same diff.

Found while opening this PR; folded in per the no-defer rule.

Refs #1879

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* docs(#2674): add Fixed changeset for the src/ trigger-list and reset fixes

Refs #1879

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* docs(#2674): restore the round-2 review corrections to the amendment

These edits were made in response to the second isolated review pass but
never staged: later commits used targeted `git add <file>` for the test and
the source fix, so the two markdown files stayed dirty and shipped nothing.
The branch carried the round-1 text, including the ADR-227 misquote the
reviewer raised as a blocker.

Restores: the unconditional-diagnostic clause (ADR-227's GSD_DEBUG opt-in
was never implemented, so citing it as the precedent was wrong), the dedup
key, #1882 folded into the out-of-band mechanism instead of a fourth
mechanism-less category, the narrowed caller-audit rationale, and the
test-methodology clause.

Refs #1879

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

.changeset/eager-tigers-greet.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 2678
+---
+**Editing `src/` no longer trips an undocumented changeset-lint failure** — CONTRIBUTING.md listed the Changeset Required triggers without `src/`, the path that compiles into every `gsd-core/bin/lib/*.cjs`, so contributors touching it hit a CI failure the docs said could not happen — and a local run of the lint reported success regardless, because it silently requires `GITHUB_BASE_REF` to see the branch at all. Both are now documented, and the config-loader test-helper that reset only one of its two warning-dedup sets now resets both. (#2674)