perf(server): bound OpenCode history hydration

[nateEc]

Closes #3601

Summary

• cap routine OpenCode thread hydration at the latest 100 messages instead of materializing the full session
• page older messages on demand when rollback needs more assistant turns
• impose a 15-second per-page timeout and pass cancellation through to the SDK request
• preserve rollback semantics across multiple history pages

Verification

• ./node_modules/.bin/vp test run apps/server/src/provider/Layers/OpenCodeAdapter.test.ts (33 passed)
• ./node_modules/.bin/vp run --filter t3 typecheck (passes; three unrelated existing Effect suggestions remain in orchestration/decider.ts)
• targeted lint and formatting for the changed files

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Note

Medium Risk
Changes how thread snapshots are built and how rollback resolves targets across paginated history; incorrect paging could mis-revert long threads, though behavior is covered by new adapter tests.

Overview
OpenCode thread hydration is capped so routine reads no longer pull the entire session history from the SDK.

readThread now loads a single page of 100 messages via session.messages (limit / optional before) instead of unbounded history. readThread therefore exposes at most the 100 most recent assistant turns—a deliberate behavior change for performance.

rollbackThread uses readOpenCodeMessagesForRollback to walk older pages only until it has enough assistant messages to pick the revert target, with deduplication and extra pagination when a full page overlaps the previous cursor.

Each history page goes through readOpenCodeMessagePage: 15s timeout, AbortSignal passed into the SDK call, and a clear timeout error on stall. runOpenCodeSdk now takes a callback (signal) => Promise<...> so cancellation can reach the client.

Tests extend the runtime mock for paged messages, hang/abort, and overlap, and add coverage for read bounds, rollback paging, overlap continuation, and timeout behavior.

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Note

Bound OpenCode history hydration to paginated reads with a 15s timeout

• readThread now reads only the latest 100 messages (one page) instead of the full session history, with a 15-second timeout per request.
• rollbackThread uses a new readOpenCodeMessagesForRollback helper that pages backwards through history only as far as needed to locate the target assistant message, deduplicating overlapping page boundaries.
• runOpenCodeSdk in opencodeRuntime.ts now passes an AbortSignal to the SDK callback so timed-out reads are cleanly cancelled.
• New tests in OpenCodeAdapter.test.ts cover page bounding, paginated rollback, overlapping-page deduplication, and timeout/abort behaviour.
• Behavioral Change: readThread no longer returns messages beyond the most recent 100; sessions with long histories will see a truncated turn list.

^{Macroscope summarized 8e48e6d.}

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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[macroscopeapp]

Approvability

Verdict: Approved

Performance optimization that bounds OpenCode history hydration to 100 messages with a 15-second timeout, preventing unbounded fetching. Changes are well-tested with comprehensive pagination and timeout test cases. No new features or schema changes—purely defensive performance improvement.

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