enhance(#3907): gates report no-input instead of a verdict they never reached (#3932)

* feat(#3907): gates report no-input instead of asserting a verdict they never reached

The three stdin-reading gates bound 2 to a stdin read error only, with no arm for stdin closed at zero bytes - so empty input flowed into the detector, found nothing, and exited 1, which each module's own comment defines as a negative verdict. An unset PHASE_SECTION made the UI gate assert the phase has no UI. Empty and whitespace-only input now exit NO_INPUT, and a read error exits UNAVAILABLE rather than a locally-invented 2, both resolved through the registry and delivered by terminateNow.

The exit code was only half of it: under --json the same input emitted {detected:false}, byte-identical to the fabricated payload #3909 exists to fix, and the blocking coverage gate reads that payload. Empty input now emits the in-tree {skipped:true,reason} form with no detected key at all.

teams-status is excluded: it never reads stdin and has no invented 2, so the four-module framing in the issue and ADR is wrong. The dead root bin/lib/ui-safety-gate.cjs is deleted - no installer reference, no workflow invocation, and the live fallback chains are for other modules. Its removal restores the unit tests to the module that actually ships; they had been asserting the stale copy's two-field shape, which is why it drifted unnoticed.

* fix(#3907): drive gate tests through the process seam, and make removed-but-needed basename-precise

CONTRIBUTING requires every subprocess go through tests/helpers/process-seam.cjs; two of the three gate suites hand-rolled spawnSync while the third, added in the same change, used runNode correctly for the identical injection case. Converted the blocks this change added, leaving pre-existing ones alone.

Deleting one of two files sharing a basename made lint-removed-but-needed report 14 references that were all to the surviving canonical module - the false-positive class its own docstring names. It now matches on the deleted file's full path when a surviving file shares its basename, which is more precise rather than weaker: a genuine full-path reference still fails, and behaviour is unchanged when no basename collides. It immediately caught a docstring on this branch that spelled the deleted path.

* test(#3907): update the one existing assertion that pinned the old empty-stdin verdict

A pre-existing test asserted exit 1 on empty stdin - the defect this phase removes - and was missed because the change added new blocks without auditing existing ones pinning the old contract. Audited the rest: the other three status-1 assertions in that file all feed real input and are the genuine-negative controls that must keep returning 1, so exactly one was stale. The retired 2 is gone from the describe's contract comment too.

* chore(#3907): backfill changeset pr number

---------

Co-authored-by: sim <sim@local>

docs/INVENTORY.md

@@ -461,9 +461,9 @@ Full listing: `gsd-core/bin/lib/*.cjs`.
 | `agent-command-router.cjs` | Thin CJS subcommand router adapter for `gsd-tools agent` |
 | `agent-install-check.cjs` | Agent-installation probe — owns `getAgentsDir` and `checkAgentsInstalled`, the single resolution the health-diagnostic agent-install rule consumes (ADR-857, #1268) |
 | `health-diagnostic-rules/agent-install.cjs` | Health-diagnostic rule: agent-installation-completeness check (W010) — the single `checkAgentsInstalled` call site's four mutually exclusive conditions, ported behavior-preserving from `cmdValidateHealth` (ADR-3180 §8.2/§8.3/§8.5, Phase 11, #3309) |
-| `api-coverage.cjs` | API-coverage detector + matrix validator (#1562, #2365) — pure `detectApiIntegration` (fail-closed: same-clause verb+noun signal + `<Service> API/SDK` surface naming a real service; strips fenced code, inline code, and path-shaped tokens; external hosts count, first-party route paths do not) and `validateCoverageMatrix`/`parseCoverageMatrix`/`renderCoverageMatrix` for the COVERAGE.md artifact (incl. the `No external API integration: <reason>` declaration); STDIN CLI (`echo "$SCOPE" \| node .../api-coverage.cjs [--json]`, exit 0=detected/1=none/2=error); consumed by the `ai-integration` capability's `plan:pre` contribution and blocking `verify:pre` gate (`check api-coverage.verify-pre`) |
+| `api-coverage.cjs` | API-coverage detector + matrix validator (#1562, #2365) — pure `detectApiIntegration` (fail-closed: same-clause verb+noun signal + `<Service> API/SDK` surface naming a real service; strips fenced code, inline code, and path-shaped tokens; external hosts count, first-party route paths do not) and `validateCoverageMatrix`/`parseCoverageMatrix`/`renderCoverageMatrix` for the COVERAGE.md artifact (incl. the `No external API integration: <reason>` declaration); STDIN CLI (`echo "$SCOPE" \| node .../api-coverage.cjs [--json]`, exit 0=detected/1=none/NO_INPUT=empty-or-whitespace-only stdin/UNAVAILABLE=stdin read failed — registry codes, ADR-3889 Phase 3, #3907); consumed by the `ai-integration` capability's `plan:pre` contribution and blocking `verify:pre` gate (`check api-coverage.verify-pre`) |
 | `artifacts.cjs` | Canonical artifact registry — known `.planning/` root file names; used by `gsd-health` W019 lint |
-| `assumption-delta.cjs` | Detects identity-model assumption transitions in phase text for discuss-phase assumptions mode (#1561) |
+| `assumption-delta.cjs` | Detects identity-model assumption transitions in phase text for discuss-phase assumptions mode (#1561); STDIN CLI (`echo "$PHASE_SECTION" \| node .../assumption-delta.cjs [--json]`, exit 0=detected/1=none/NO_INPUT=empty-or-whitespace-only stdin/UNAVAILABLE=stdin read failed — registry codes, ADR-3889 Phase 3, #3907) |
 | `audit-command-router.cjs` | ADR-959 capability command router for `gsd-tools audit-uat` and `gsd-tools audit-open` — extracted from hardcoded cases in `gsd-tools.cjs`; dispatches to `uat.cjs:cmdAuditUat` and `audit.cjs:{auditOpenArtifacts,formatAuditReport}`; phase 4d-impl-3 |
 | `audit.cjs` | Audit dispatch, audit open sessions, audit storage helpers |
 | `capability-activation.cjs` | Capability activation resolver shared by config validation and capability-state consumers — resolves registry-owned config keys from raw runtime config without re-centralizing migrated settings |
@@ -655,7 +655,7 @@ Full listing: `gsd-core/bin/lib/*.cjs`.
 | `uat.cjs` | UAT file parsing, verification debt tracking, audit-uat support |
 | `uat-predicate.cjs` | UAT-passed predicate — markdown-aware evaluation of HUMAN-UAT results; returns pass only when all required checks pass; ignores false-positive contexts (frontmatter, fenced code, blockquotes, HTML comments) |
 | `ui-consideration-probe.cjs` | Spec-completeness UI-consideration probe (compiled from `src/ui-consideration-probe.cts`, gitignored) — the third adapter of the `probe-core` resolution model (ADR-550 Decision 7): element-kind classification, applicable-category relevance filter, consideration proposal, `proposeElements`/`autoResolve` (propose-then-confirm + the `--auto` never-dismiss floor), and the `{explicit, backstop}` validators; delegates merge/rollup/CLI to `probe-core`; exports `classifyElement`, `applicableCategories`, `proposeConsiderations`, `proposeElements`, `autoResolve`, `analyzeCoverage`, `UI_TAXONOMY` (#1867) |
-| `ui-safety-gate.cjs` | Shell-free word-boundary UI token detector (#3706, #3718); reads phase-section text from stdin, exits 0 (UI found) or 1 (no UI); also deployed to `gsd-core/bin/lib/` so the GSD installer ships it to `$RUNTIME_DIR` (#448) |
+| `ui-safety-gate.cjs` | Shell-free word-boundary UI token detector (#3706, #3718); reads phase-section text from stdin, exits 0 (UI found), 1 (no UI — real input, examined), NO_INPUT (empty/whitespace-only stdin) or UNAVAILABLE (stdin read failed) — the latter two are registry codes (ADR-3889 Phase 3, #3907); also deployed to `gsd-core/bin/lib/` so the GSD installer ships it to `$RUNTIME_DIR` (#448) |
 | `ui-frontend-evidence.cjs` | Static frontend-evidence detector (compiled from `src/ui-frontend-evidence.cts`, gitignored) — plan-time structural corroboration for `computeUiPlanGate` (#3312): a `package.json` UI-framework dependency or a component-framework file (`*.tsx/*.jsx/*.vue/*.svelte`) in the tree, so a UI-token match on a hyphenated proper noun (e.g. repo `dashboard-financeiro`) cannot block planning in a repo with no frontend; mirrors the post-wave `computeUiSafetyGate` git-diff corroboration |
 | `unusable-input.cjs` | Deduplicates stderr diagnostics for corrupt or unreadable configuration (#1879) |
 | `update-context.cjs` | Pure install-context resolver for `/gsd-update` — runtime/scope/config-dir/version detection (LOCAL/GLOBAL/UNKNOWN) ported from update.md bash; backs `gsd-tools update-context` (#498) |