feat(task): persist task thinking effort on history items (DTE series 2/5)

[easonLiangWorldedtech]

≤400-line redo of Zoo-Code-Org#1338 — DTE series 2/5, unit 4/5

Persistence for the task-local thinking effort: the history-item schema
fields, taskMetadata propagation (key-presence contract), the Task
constructor restore, and the abort/dispose snapshot ordering. Also lands the
dispose boundary group split out of PR #38 per plan §2.6 — the task-end
override reset, its DTE JSDoc, and its test block.

Stack

• Base: feat/dte-v2-3-task-runtime-effort @ 4075c8a75 (U3, PR feat(task): task-local runtime thinking effort state with per-request override (DTE series 2/5) #38 — amended in place with its 3 mutation-killing assertion lines; U4 rebased onto it)
• Content source: feat/dte-trial-all union 27a2e97df (tag dte-legacy/union), U4 slice
• Related: DTE-v2 final ship plan - 39-unit 400-line redo of the DTE series (supersedes #28) #35 (DTE-v2 tracking ledger)

Budget (plan §2: a+d ≤ 400)

5 files changed, 248 insertions(+), 5 deletions(-) = 253 ≤ 400 ✓

File	a+d
src/core/task/Task.ts	36+/2−
src/core/task/__tests__/Task.runtime-thinking-effort.test.ts	111+/2−
src/core/task-persistence/__tests__/taskMetadata.spec.ts (new)	81+
src/core/task-persistence/taskMetadata.ts	13+/1−
packages/types/src/history.ts	7+/0−

Provenance / fidelity

• 3-way git merge-file per file — base 90b47b053 (U3 tip, before the U4
  work), ours = U3 head, theirs = 77ec064d3 (U4 tip). Task.ts and
  taskMetadata.ts merged clean (0 conflicts). history.ts had 2 conflicts
  where main's newer pendingTaskAction schema met the DTE import/fields —
  resolved by keeping both (imports alphabetical, DTE block above the
  pendingAction field; result = 7+/0− over U3 head).
• taskMetadata.spec.ts (new, 81 lines) is the byte-exact 77ec064d3
  version. The runtime-effort test is the byte-exact 77ec064d3 version
  (394 lines) plus the same 3 mutation-killing assertion lines that landed
  with U3 (PR feat(task): task-local runtime thinking effort state with per-request override (DTE series 2/5) #38) plus the 13-line constructor-restore killing test added by
  the mutation-diff fix below — 410 lines total; both carry no U5/U14 content.
• Task.ts dispose boundary group (task-end reset + DTE JSDoc, 9 lines) and
  the 13-line describe("dispose") test block are the content PR feat(task): task-local runtime thinking effort state with per-request override (DTE series 2/5) #38 split
  out under plan §2.6; they land here with the persistence work, matching the
  plan's U4 scope ("persistence + boundary cases").
• src/eslint-suppressions.json: untouched (no U4-owned count changes).

Out of scope (next unit)

• U5 (DTE-2d): the Anthropic output_config.effort adaptive envelope.

Mutation-diff fix (killing test, plan L42 — same PR)

The first CI mutation-diff run (head ac085bbe6, base d0b1a3dcd)
reported 1 Survived ConditionalExpression mutant (replacement: true) on
the constructor restore guard if (historyItem.thinkingEffort)
(Task.ts L594). Mechanism note: Stryker v10's ConditionalExpression
mutator mutates if-tests (the ?: ternary branch is commented out in
the mutator source), so this is the guard's condition → true.

It survived because the redundant restore call it introduces,
setRuntimeThinkingEffort(undefined, undefined), hits the setter's
already-inactive early return and leaves no observable state change — the
existing "leaves the override inactive" it only asserts state. Fix (same
PR): a 13-line it("never calls the restore path when the history item has no persisted effort") with a vi.spyOn(Task.prototype, "setRuntimeThinkingEffort") call-count assertion — fails on the mutant,
passes on the real guard.

Local dev-stage gate on the amended head (§5.1):
node scripts/stryker-diff.mjs ci --base 4075c8a75 --head 111cf40ae →
extension 22 changed lines, 10 ranges, exit 0, 0 Survived.

Verification (local)

• pnpm --dir src exec eslint --prune-suppressions --max-warnings=0 on the four src files → exit 0, no count change
• pnpm check-types → 11/11 projects
• pnpm --dir src exec vitest run core/task/__tests__/Task.runtime-thinking-effort.test.ts → 16/16 (3.81 s); core/task-persistence/__tests__/taskMetadata.spec.ts → 3/3 (unchanged by this amend)
• git diff --shortstat 4075c8a75 HEAD → 248+/5− = 253 ≤ 400 (the 3 shared killing-assertion lines already sit in the U3 base and do not appear in this diff)
• mutation-diff gate (dev stage, §5.1) on the amended head → exit 0, 0 Survived (see fix above)

[easonLiangWorldedtech]

Superseded — U4 will be opened on upstream (Zoo-Code-Org/Zoo-Code) when its stack slot opens (max 3 open DTE-v2 PRs, ship plan 2.2). Head 111cf40 unchanged.