fix(workflows): recover terminal artifact commits

[testikun]

Problem

Workflow terminal persistence writes result.json, transcripts.json, optional journal.json, and the final referencing workflow.json as separate atomic replacements. A process crash after the side artifacts but before the final manifest can leave the earlier manifest without references and the terminal evidence orphaned.

Current main already publishes a reference-free terminal manifest first, which prevents a known terminal run from remaining running, but it cannot prove that an otherwise orphaned artifact belongs to a complete terminal commit.

Closes #110.

Value

Restart recovery can now distinguish a fully prepared terminal artifact set from partial, stale, substituted, or malformed files. Exact terminal results remain discoverable after the crash window without treating an arbitrary result.json as completion evidence.

Approach

• Write one bounded, versioned .workflow-commit.json receipt before the terminal side-artifact sequence. It records the exact final manifest plus the fixed artifact names, byte counts, and SHA-256 digests.
• Keep workflow.json canonical: publish the existing reference-free terminal projection first, prepare every side artifact, atomically commit the exact recorded manifest last, then remove the receipt.
• Recover at the persisted Workflow read boundary and before delivery-state mutation. Promotion requires an exact run-directory identity, known terminal status, fixed path whitelist, matching manifest references, regular non-symlink files, byte budgets, lengths, and digests.
• Leave incomplete or invalid receipts fail-closed; a normal retry replaces the single fixed receipt. Legacy runs without receipts retain their old behavior, and orphan result.json alone never proves completion.
• Document the ownership, sequence, recovery outcomes, compatibility, and fsync limitation in docs/architecture/WORKFLOW_ARTIFACT_COMMIT.md, linked to workflows: terminal artifact set (result.json + workflow.json) is not committed atomically #110.

Validation

• bun run check — passed.
• Focused artifact and dashboard tests — 42 passed, 0 failed.
• bun run test — Node tests: 1247 passed, 0 failed, 1 skipped; Vitest: 30 passed.
• Regression cases include complete crash recovery, missing artifacts, same-size digest substitution, already-committed idempotence, delivery update after recovery, dashboard/startup hydration, normal cleanup, and dependent-write failure.

Impact

• User-visible behavior: no UI changes.
• Model-visible context/tools: none.
• Runtime/lifecycle: terminal Workflow artifact persistence gains a recoverable commit receipt at the existing filesystem boundary.
• Persisted config/data: no configuration changes. New terminal writes may briefly contain .workflow-commit.json; successful writes remove it, and legacy artifacts remain readable.
• Compatibility/risk: filenames and canonical manifest references remain unchanged. Recovery fails closed on unknown versions, identities, paths, states, sizes, symlinks, or hashes. The guarantee covers process-crash recovery at the existing atomic-rename boundary, not power-loss durability beyond writeFileAtomic.

[testikun]

CI status note: Node 22/24 completed this PR's repository checks and failed only at the final fresh-install Smoke-test packed standalone Web CLI step, where the child exits before the test can read its URL. The same failure now occurs on unrelated PRs #385, #386, and #387.

I reproduced the packed install independently: npm now admits Pi 0.85.0 through OpenPI's published peerDependencies: "*"; the CLI then exits with Cannot find module '@earendil-works/pi-server'. The checkout/lock-based bun run check and full test suite remain green. I recorded the shared packaging regression and suggested peer-range follow-up in #328: #328 (comment)

No dependency workaround is mixed into this feature PR.