[Fix] Live transcript converges to persisted envelopes on every history refetch

[daniel-lxs]

What problem this solves

Root-cause fix for the live-session transcript corruption from the steering test pass (tasks 190holbb4xm2k, 11nl0xsy05oyl on openmote): transcripts collapsing to the initial prompt + latest answer after a reload, blank renders mid-session, steered messages rendering out of chronological order, and missed live replies staying missing — always self-resolving once the sandbox slept (historical rendering was always correct, and server envelope data was always intact).

Root cause

The live page reconstructed history through two different code paths:

• Initial load: loadAcpEnvelopes — the envelope-aware builder the historical view uses (always correct).
• Every subsequent refetch: _mergeAcpHistory patched the in-memory list envelope-by-envelope through the live-event handler, and skipped any envelope whose id was already present.

The skip-by-id rule means any drift in the live in-memory state (missed socket events, replacements at stale indexes, ordering skew) could never be corrected by a refetch — it persisted until the sandbox slept and the page fell back to the historical loader.

What changed

• _mergeAcpHistory now rebuilds the transcript from the fetched envelopes with the same loadAcpEnvelopes builder, then carries over only messages the fetch doesn't cover yet: optimistic sends and live-only events, matched via logical event id, user clientMessageId, toolCallId, or the originating event timestamp. Every refetch — which fires on every socket (re)connect — is now a convergence point to the server's authoritative transcript.
• Duplicate live/persisted twins resolve to the persisted message (its id is the durable anchor reloads and the historical view use). One existing test expectation updated accordingly.
• An identical refetch returns the exact previous references (no re-render churn).

Provability

The new steered-task-history.client.test.ts suite (7 tests) includes a drift-healing case — content corrupted under a matching envelope id — that fails against the previous merge implementation (verified: 1 failed / 6 passed on the old code) and passes with the rebuild. Also covered: collapse-recovery to full transcript, carried-over optimistic + unpersisted live messages, timestamp ordering for envelopes the socket missed, and the no-change fast path.

Validation

Full src/app/(sandbox)/task/ suite green (483 tests, incl. the 64-case store suite), pnpm lint:fast + check-types:fast clean.

🤖 Generated with Claude Code

[roomote-roomote-v1]

2 issues outstanding. See task

• apps/web/src/app/(sandbox)/task/[taskId]/hooks/use-sandbox-store.ts:852 preserves stale todo state when server history clears todos: rebuilt.todos.length > 0 ? rebuilt.todos : state.todos keeps the old list even when the rebuilt history's latest plan is intentionally empty, so a refetch cannot converge the sidebar todo state to server truth. Use rebuilt todos directly when history includes a plan/todowrite result, including empty arrays.
• apps/web/src/app/(sandbox)/task/[taskId]/hooks/use-sandbox-store.ts:854-865 calls acpService.setMessages(...) immediately after loadAcpEnvelopes(...), which resets the protocol service and discards pending request/user lookup state populated from history. After a refetch over a pending request_user_input, a subsequent live request_user_input_response formats with request === null, so secret answers are no longer masked by formatRequestUserInputResponseText and can render raw in the transcript; preserve or rebuild those service maps instead of clearing them.