docs(engine): mark the usage-limit terminal filters DELIBERATE-LITERAL — a documented false positive that has now baited two workers (#2767)

## No behaviour change. This is the work order retracting a documented
false positive.

I went to convert the `done`/`archived` filters in
`usage-limit-detector.ts`, reasoning that on a renamed board a provider
rate limit would pause already-finished work. I wrote the conversion —
and only then read the note a previous worker had left directly above
it:

> *"The FIRST thing I suspected there — the `done`/`archived` terminal
filter — turned out to be a **FALSE POSITIVE**: its revert stayed green,
because the lane check already excludes finished cards."*

**They are right and I was wrong.** A terminal card is already excluded
downstream: `taskUsesProvider` resolves the task's active lane, a
finished card matches no active lane, so it resolves no providers and
cannot be affected. The suite pins exactly this — `pauses a PEER
executing in the renamed WIP column` asserts `FN-SHIPPED` is not paused.

My conversion is reverted. It changed nothing at runtime and would have
lowered the census count while behaviour stayed identical — the precise
shape this program keeps warning about, produced by me this time.

## Why a marker and not just the existing prose

The note was already there and I walked into it anyway, because **the
census kept listing this file as 4 unconverted guards**. The work order
advertised the work; the reasoning against it lived in a comment you
only reach after you have started. Prose informs a reader who is already
looking; a marker informs the *instrument*, so the file drops out of the
work order.

Two distinct reasons are recorded rather than one blanket marker,
because they are not the same argument:

- **the prefilter** is a deliberate cheap **superset** (#2672 review).
Converting it reintroduces the whole-board resolution that review
removed. Literals are safe here in the direction that matters — a
renamed board declares no `done`/`archived` id, so nothing is wrongly
*excluded*.
- **the final filter** is redundant with the lane check, and that
redundancy is already proven by an existing test.

## Census

| | before | after |
|---|---|---|
| `usage-limit-detector.ts` | 4 | **0** |
| repo backlog | 437 | **433** |
| DELIBERATE-LITERAL (reviewed) | 38 | **42** |

Every one of the 4 is a marker, not a conversion. The backlog moved
because reviewed literals left it honestly, not because behaviour
changed.

## Verification

`usage-limit-detector.test.ts` **58 passed**, unchanged before and after
· `pnpm test:gate` **10 / 158 / 487 / 71** · `pnpm lint` clean · engine
`tsc --noEmit` **0 errors** · `--strict` exits 0.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/lib/lifecycle-column-census-baseline.json

@@ -20,7 +20,6 @@
     "packages/engine/src/agent-heartbeat.ts": 4,
     "packages/engine/src/replan-target.ts": 4,
     "packages/engine/src/triage.ts": 4,
-    "packages/engine/src/usage-limit-detector.ts": 4,
     "packages/core/src/async-mission-store-queries.ts": 3,
     "packages/core/src/task-priority.ts": 3,
     "packages/core/src/task-store/async-merge-coordination.ts": 3,
@@ -131,6 +130,8 @@
     "packages/dashboard/app/components/TaskDetailModal.tsx\u0000triage": 2,
     "packages/engine/src/scheduler.ts\u0000in-progress": 2,
     "packages/engine/src/scheduler.ts\u0000in-review": 2,
+    "packages/engine/src/usage-limit-detector.ts\u0000archived": 2,
+    "packages/engine/src/usage-limit-detector.ts\u0000done": 2,
     "packages/cli/src/commands/task.ts\u0000archived": 1,
     "packages/cli/src/commands/task.ts\u0000done": 1,
     "packages/cli/src/extension.ts\u0000archived": 1,