fix(compaction): let the core route claim the idle warm summary

[code-yeongyu]

Problem

senpi pre-generates a summary while your session sits idle so you never wait for compaction. PR #853 taught the extension route to reuse it. The core route still threw it away.

The ordering is deterministic, not a race — on a new prompt _enforceCompactionBeforeProvider runs before emitBeforeAgentStart, so core always reaches compaction first, and its handler called invalidateSpeculativeCompaction() as its first statement. Measured with a file probe on the real CLI:

IDLE_TRIGGER
CORE_ROUTE_ENTER reason=threshold hasJob=true   # core arrives first, job alive
BLOCKING_ROUTE_ENTER hasJob=false               # already destroyed

So the warm-up was aborted and re-billed in exactly the case it exists for.

Fix

Claim the job for the core route instead of invalidating it:

• Atomic — detached synchronously before any await, so exactly one route can own it.
• Not aborted — the controller is deliberately left alive; aborting is what destroyed the finished work.
• Narrow — the claim holds only for an automatic compaction with no custom instructions, a speculative origin, the same model identity, a valid WarmAnchorSnapshot, and a boundary equal to core's own preparation.firstKeptEntryId. Every other case falls through to the existing fresh generation, unchanged.

Manual compaction keeps its own instructions, a landed boundary still forces regeneration, and a mismatched cut is refused — each covered by a test.

Verification

Real-CLI A/B (core-route-warm-handoff-qa.mjs, RPC + mock provider, sandboxed HOME) — a genuine defect reproduction:

	baseline 3358d48ff	this branch
result	7/9	9/9
warm_consumed	0	1

• Unit: RED expected 'fresh summary…' to contain 'warm summary…' → GREEN; 4 cases incl. three safety paths.
• test/compaction/ 346 passed (344 before).
• Invariant files green: speculative-budget-handoff, required-compaction-deterministic-fallback, warm-summary-anchor, stale-warm-blocking-repro, metadata-side-effects, lifecycle, idle-compaction, speculative-abort-cancellation, suite/compaction-race, suite/agent-session-compaction — 88 tests.
• Root npm run check exit 0.

Scope note

An AgentSession-level test cannot drive this: shouldRunIdleCompaction requires a persistent mode (tui/rpc/app-server) and the vitest harness runs in print, so the warm-up never starts there. The end-to-end proof is the RPC QA scenario above, which runs in a real persistent mode.

---

Summary by cubic

Reuses the idle warm summary in the core route so users don’t wait for a second compaction. Previously core always invalidated the speculative job and regenerated; now it claims the job when safe, returns its result, and reliably aborts any unused claim, including on thrown exits.

• session_before_compact calls claimWarmSummaryForCoreRoute() before invalidation. The claim detaches the job synchronously, logs warm_consumed with route: "core-route" on success, and uses a try/finally to abort the controller unless the result is consumed (covers early returns and exceptions).
• Claim conditions: automatic compaction (no custom instructions), speculative origin, same model identity, valid warm anchor on the current branch, and a boundary equal to preparation.firstKeptEntryId. Otherwise it regenerates.
• Manual compaction, landed boundaries, and mismatched cuts still regenerate. Covered by core-route-warm-handoff.test.ts. Adds a real-CLI QA scenario to verify warm_consumed and that core does not regenerate.

^{Written for commit 4c91dfd. Summary will update on new commits.}

[code-yeongyu]

Test (workspaces + scripts) is red on main, not from this PR

The failing assertion is in scripts/prepare-senpi-bundled-workspaces.test.mjs:191 — an unexpected which: '1.0.0' in the bundled workspace dependency set:

+ actual - expected
  {
    '@earendil-works/pi-ai': 'npm:@code-yeongyu/[email protected]',
    'cross-spawn': '7.0.6',
+   which: '1.0.0'
  }

Reproduced on pristine origin/main (3358d48), same machine, no changes from this branch:

npm run test:scripts
ℹ pass 138
ℹ fail 1
✖ which: '1.0.0'

This branch produces the byte-identical failure. Nothing in the diff touches package.json, the lockfile, or the bundling scripts — it changes one compaction handler, adds a test file, and adds a QA scenario.

The bundled-dependency drift deserves its own fix rather than being bundled into a compaction change.