[TinBane]

provider recovery must create a genuinely fresh native session before recording a portable context replacement. an adapter that returns its existing session can otherwise record a recovery that never happened, and a failed-resume retry can silently continue on that reused session.

merged current main without rebasing and preserved its broader overflow recovery, history selection, and background-work guards. the remaining change rejects missing or unchanged native identities without retrying the invalid replacement, and persists replacement handoff events only while the same run attempt is still starting. no client or wire changes.

verification: blacksmith vp run check:changed passed format, lint, knip, graphql, three affected package typechecks, and 99 tests. existing test tables reproduce reused-session overflow, failed-resume retry bypass, and cancellation during replacement before the fix and pass afterward. two independent gpt-6.1-sol reviews approved fd8380928a5e62fb38da67c12139c1f3ea88665e with no actionable findings. live authenticated provider/client behavior on this updated head is unverified; earlier runtime evidence remains in the discussion.

maintainer takeover authorized by maria. model and harness: gpt-6.1-sol through codex.

[macroscopeapp]

Approvability

Verdict: Needs Human Approval

Macroscope's review found this PR requires human approval — This PR adds substantial production orchestration for budget-based provider-thread replacement and portable context delivery, changing native session and durable handoff state during turn startup. The replacement path has an unresolved high-severity concern about preflighting the complete handoff set, so the runtime behavior merits human review.

Needs human approval because:

• 1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

^{Adjust the Minimum Blocking Severity for this repo — including turning it Off — in Settings. You can add or adjust custom eligibility rules. Learn more.}

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Walkthrough

Context handoff delivery now uses a planner to select pending handoffs and check history against a budget. Provider turn startup preflights qualifying provider-switch handoffs and can replace the native thread when the current plan overflows.

Changes: Context handoff delivery and provider switching

Layer / File(s)	Summary
Plan and deliver context handoffs apps/server/src/orchestration-v2/ContextHandoffDelivery.ts, apps/server/src/orchestration-v2/ContextHandoffDelivery.test.ts	The exported planner selects pending handoffs, builds and selects history, and returns an empty, ready, or overflow plan. Delivery uses the plan. A test verifies that empty handoffs do not evaluate the budget callback.
Prepare and persist native-thread replacements apps/server/src/orchestration-v2/ProviderTurnStartService.ts	A shared replacement path creates a fresh native binding and persists handoff and transfer events only while the run attempt is starting. Resume-failure handling uses this path.
Preflight provider-switch handoffs apps/server/src/orchestration-v2/ProviderTurnStartService.ts, apps/server/src/orchestration-v2/testkit/ProviderSwitch.integration.test.ts	Provider turn startup derives usage state and checks handoffs against the current budget. If the plan overflows, it checks a fresh-thread budget and replaces the native thread only when that plan is ready. Integration scenarios check replacement, failure, and compact-input outcomes.

Estimated code review effort: 4 (Complex) | ~45 minutes

Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant ProviderTurnStartService
  participant planContextHandoffDelivery
  participant NativeThreadReplacement
  ProviderTurnStartService->>planContextHandoffDelivery: Plan with current context budget
  planContextHandoffDelivery-->>ProviderTurnStartService: Return overflow
  ProviderTurnStartService->>planContextHandoffDelivery: Plan with fresh-thread budget
  planContextHandoffDelivery-->>ProviderTurnStartService: Return ready plan
  ProviderTurnStartService->>NativeThreadReplacement: Replace native thread

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Possibly related issues

• pingdotgg/t3code#15997 — The changes preflight provider-switch handoffs that can exceed the current budget and replace the native thread.
• pingdotgg/t3code#22198 — The changes check whether a full-thread handoff fits a fresh-thread budget.
• pingdotgg/t3code#23275 — The changes preflight handoff delivery and provide a replacement path for eligible overflow.
• pingdotgg/t3code#22636 — The changes can create a fresh native thread when a provider-switch handoff fits its budget.

Suggested reviewers: maria-rcks, t3dotgg, juliusmarminge

Merge Risk: Moderate · up to c26e1

Provider-switch turns can unnecessarily replace a working native thread with portable context, losing native session state. Align the preflight's delivered-item set with real delivery before merging.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title is concise, specific, and accurately describes the main server-side fix for oversized provider handoffs.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description check		The description covers the problem, implementation, scope, and verification. It identifies the recovery failure mode, explains the fresh-session and run-attempt safeguards, reports focused checks and …

Full details: Description check

Explanation

The description covers the problem, implementation, scope, and verification. It identifies the recovery failure mode, explains the fresh-session and run-attempt safeguards, reports focused checks and test results, and notes that live authenticated provider behavior remains unverified. It does not use the template headings or provide a linked issue or approval comment, but the required information is mostly present.

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Actionable comments posted: 1

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Inline comments:
Review comments at
@apps/server/src/orchestration-v2/ProviderTurnStartService.ts:
- Around line 1050-1057: Update the ACP overflow replacement flow in
replaceNativeThread so it creates or activates a fresh native session instead of
allowing AcpAdapterV2.ensureThread to reuse the resumed activeSessionId.
Preserve normal thread adoption behavior for non-replacement paths.

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Review comments at
@apps/server/src/orchestration-v2/ProviderTurnStartService.ts:
- Around line 1023-1028: Update the overflow preflight in the deliveryInput
setup to populate alreadyDeliveredItemIds with settled item IDs for
loadedProviderThread.nativeThreadRef, using the same target-thread and
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[maria-rcks]

Note

Written by gpt-6.1-sol on behalf of Maria

thanks @TinBane. the shared delivery planner and preflight of the prepared replacement handoff were the right foundation. i kept your commits and merged current main, then added the fixes on top.

• preflight and delivery now share the same ordered handoffs and settled-item deduplication.
• acp explicitly creates a fresh session through its existing safe replacement helper, preserving normal resume behavior and failure cleanup.
• replacement preserves native state when fresh capacity is unknown, prepared messages would be dropped, background work is pending, or the attempt was cancelled. unchanged native identity fails before replacement bookkeeping.
• removed duplicate scans, shared the acp reset path, and moved the standalone test into the existing budget tests. no new test files or client/wire changes.

verification: reproduced the failure on main and the safety regressions before fixing them. blacksmith vp run check:changed passes format, lint, knip, graphql, typechecks for 21 affected packages, and 158 tests. all 28 ci checks are green on 0e73689c9fa07a50651c69ac85dd5a0a54c4f36f.

verification transcript

unverified: live authenticated codex/claude-to-client behavior; this vm has no provider credentials. maintainer verification and approval remain required. coderabbit paused automatically; i did not invoke it.

@TinBane: muse currently returns its existing native session for replacement. this now fails safely without recording a false replacement handoff; muse support can follow separately.

[TinBane]

Thanks for picking this up. Happy to take the Muse follow-up as its own PR once this lands, tested against a live Muse session.

[maria-rcks]

Note

Written by gpt-6.1-sol on behalf of Maria

Verified in a real dev environment

verified the exact head 0e73689c9fa07a50651c69ac85dd5a0a54c4f36f in this linux boat vm, with a background vp run dev, task-local state, repository playwright, /usr/bin/google-chrome, and real codex gpt-6.1-sol through the local proxy. created the local git project, provider instances, and conversation through the app. no mocks, fixtures, replay data, telemetry edits, or source changes.

• switched between two codex instances with separate homes. small portable handoffs preserved context and resumed the same native sessions on return.
• returned to the second instance with a 178,910-byte current prompt, below the client character limit. its real usage was 15,030 of 258,400 tokens, making the resumed handoff budget zero and the fresh budget 14,890 bytes.
• the server logged handoff_overflow and replaced native session 01a18a86-e924-76d2-b383-0939614d1599 with 01a18a8a-4c26-7010-a5c5-bf893e4f5e96. persisted full-history and delta handoffs were injected with no omitted items. the real model returned maple-24579 birch-24579, including the codeword introduced on the other instance after this session's last turn.
• a normal follow-up completed on that same replacement native session. the recording shows this neighboring interaction.
• blacksmith ran vp i && vp test run apps/server/src/orchestration-v2/testkit/ProviderSwitch.integration.test.ts apps/server/src/orchestration-v2/ContextHandoffBudget.test.ts: 2 files and 60 tests passed. recorded ci at this head has 28 successful checks, none pending or failing. no push was needed.

baseline finding: first ran github/main at 44d508fd8b in ../main, installed with vp i, and exercised the same conversation. current main already recovers the overflow through https://git.cafe/pingdotgg/t3code/pulls/25610 (07242abff3), logging handoff_budget_exhausted and returning both codewords. the original bug therefore did not reproduce on today's main. these are baseline/head captures, not a failure/success comparison. padding lengths differ to compensate for the two sessions' real usage.

read-only runtime transcript, native identities, handoff delivery and check results

Not verified

native electron, ios/android, macos/windows, relay/tunnel and multi-device connections; this pass used the linux web client. claude was not authenticated. live acp, muse, cursor, grok, opencode and antigravity paths were not exercised. compact/restart, cancellation/background-work races, unknown capacity and inputs too large even for fresh history were covered only where the existing focused tests exercise them, not with real providers in this pass. full check:changed was not rerun because no source changed. the separate recovery already on main needs maintainer consideration before integrating this older implementation; i did not rebase, merge, close, change labels, or push.

[TinBane]

Thanks for the live check. Agreed that #25610 supersedes this. I compared the two:

• fix(server): recover handoffs when target context is exhausted #25610 recovers in cases this PR declines. It estimates context use when the provider reports none, includes earlier failed or interrupted runs, and recovers with a bounded selection when not every history item fits. This PR needed measured usage and refused if any item would be dropped.
• fix(server): recover handoffs when target context is exhausted #25610 has stronger guards. It checks for background work before replacing a Claude process or ACP session, and gives a clear error when that blocks recovery.
• Two safeguards here aren't on main. This PR rejected a "fresh" session that came back with the same native id. Muse does that today, so main records a recovery handoff that never happened, then fails with "shorten the request". After a failed resume, the retry quietly runs the turn on the reused session. This PR also wrote replacement events only while the attempt was still current.

I've put those two on top of main, with tests, in #27517. Happy for this one to be closed.

[t3dotgg]

Note

🤖 GPT-6.1 Terra [1m] responding on behalf of Theo

Closing at the author’s request because the broader handoff recovery fix merged and the remaining safeguards moved to a separate PR. #24579 comment #25610