fix(engine): assignment load must be resolved per task — #2787 P1 follow-up (#2796)

Fix-forward for the P1 that arrived on **#2787 after it merged** — so it
lands as its own PR rather than a thread reply on merged code.

## The finding

`selectPermanentAgentForTask`'s `activeColumns` was resolved from the
**candidate** task's workflow and then applied to every row `listTasks`
returned. On a project running several workflows — the normal case —
assignments living in another workflow's load-bearing lanes vanished
from the tally, and the already-loaded-agent-wins bug returned through a
different door.

**A column id means something only relative to its OWN workflow.**
`blocker-fanout.ts` documents exactly this and offers a per-task
`classify`; the option is now that same shape rather than a third
invention:

```ts
countsAsAssignmentLoad?: (task: Task) => boolean
```

The scheduler resolves each assigned row against its own IR, sharing one
cache for the selection, so a board spanning three workflows reads three
IRs — not one per assigned card.

## Why this is the third round on the same parameter, stated plainly

1. I added the parameter and **never wired the caller** — inert in
production.
2. I wired it as a **union of wip+review**, which dropped hold/intake
and made it a *regression* for backlog work.
3. I resolved it from **one workflow** and applied it to all — this fix.

Each round was a smaller version of the same error: treating a lane
answer as global when it is per-task, and per-role when it is
per-membership. Worth recording because the first two rounds both looked
correct and both passed their tests — the tests asserted the renamed
case I was thinking about, not the shape of the data.

## Verification

- new cross-workflow case; reverting the predicate to a single
workflow's lanes **fails it**
- `agent-assignment` suite **14 passed**
- `pnpm test:gate` — **161 / 13 / 487 / 71** · lint clean · census
`--strict` exits 0

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

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

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

@@ -101,6 +101,8 @@
   },
   "deliberateByFile": {
     "packages/dashboard/src/reliability-metrics.ts\u0000in-review": 4,
+    "packages/engine/src/scheduler.ts\u0000in-progress": 3,
+    "packages/engine/src/scheduler.ts\u0000in-review": 3,
     "packages/core/src/live-agent-count.ts\u0000in-progress": 2,
     "packages/core/src/live-agent-count.ts\u0000in-review": 2,
     "packages/core/src/store.ts\u0000in-review": 2,
@@ -109,8 +111,6 @@
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     "packages/dashboard/app/components/TaskCard.tsx\u0000triage": 2,
     "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,
     "plugins/fusion-plugin-reports/src/store/report-store.ts\u0000archived": 2,
@@ -154,6 +154,7 @@
     "packages/engine/src/project-engine.ts\u0000in-review": 1,
     "packages/engine/src/scheduler.ts\u0000archived": 1,
     "packages/engine/src/scheduler.ts\u0000done": 1,
+    "packages/engine/src/scheduler.ts\u0000todo": 1,
     "packages/engine/src/triage.ts\u0000triage": 1,
     "plugins/fusion-plugin-even-cards/src/cards/board-cards.ts\u0000archived": 1,
     "plugins/fusion-plugin-even-cards/src/cards/board-cards.ts\u0000done": 1,