[t3dotgg]

Forked threads got vague titles. A fork has no messages of its own, so its first title came from one follow-up message with no context. "ok now do the same for mobile" became "Port Changes to Mobile App".

Title generation now reads the source thread's messages up to the fork point, across forks of forks. It sends them with the source title to the shared title prompt. A new prompt section asks for the inherited subject plus the fork's new direction. All providers use this prompt, for first titles and for regeneration. If the source is gone, the fork falls back to its own messages.

Same fork, real model, two runs each:

Prompt	Titles
Before	"Apply same change to mobile app", "Port Changes to Mobile App"
After	"Mobile App Sidebar Row Re-renders", "Sidebar Row Re-renders in Mobile App"

Proof: a new service test fails on main and passes here, plus the live model comparison above.

Reviewed with sol-loop: 2 rounds with GPT-6.1 Sol. Sol verdict: approved

Created with Claude Opus 5.5 in Claude Code (T3 Code).

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	5.0 KiB	5.0 KiB	−7 B (−0.1%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	−7 B (−0.6%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: 375da0f · PR result: eab7804 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Approved at eab7804

Macroscope's review found this PR approvable — This is a scoped server bug fix that enriches title generation only for forked threads, while preserving existing non-fork behavior and handling missing source threads. The added regression test verifies the fork-point history selection and excludes rolled-back or later messages.

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[coderabbitai]

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Recent review info

Run configuration

• Source mode: Auto
• Repository: pingdotgg/t3code
• Branch: t3/fix-forked-thread-title-context
• File: .coderabbit.config.ts
• Commit: eab7804
• Layers: Repository TS config
• Review profile: CHILL
• Plan: Team
• Run ID: 44edbb04-d7fe-498b-9c97-ad124525ab62

Commits

Reviewing files that changed from the base of the PR and between ecb8c98 and eab7804.

Files selected for processing: 2

• apps/server/src/orchestration-v2/ThreadTitleRegenerationService.test.ts
• apps/server/src/orchestration-v2/ThreadTitleRegenerationService.ts

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Walkthrough

Thread title regeneration now gathers inherited history through a fork’s selected run. It passes the source title and history to title-generation prompts, which identify post-fork content when fork context is present.

Changes: Fork-aware title generation

Layer / File(s)	Summary
Prompt context contract and formatting packages/provider-core/src/server/textGeneration.ts, packages/provider-core/src/server/textGenerationOperations.ts, packages/provider-core/src/server/textGenerationPrompts.ts	Title generation accepts optional fork-source context. Prompts include the source title and history, limited to 8,000 characters, and label content as post-fork when context is present.
Inherited history collection and verification apps/server/src/orchestration-v2/ThreadTitleRegenerationService.ts, apps/server/src/orchestration-v2/ThreadTitleRegenerationService.test.ts	Regeneration collects user and assistant messages through each fork point, excluding streaming messages and applying the runless-message rule for v1_import history. A test checks that history after the selected fork run and rolled-back history are excluded.

Priority: Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant ThreadTitleRegenerationService
  participant OrchestrationV2AppThread
  participant generateThreadTitle
  participant buildThreadTitlePrompt
  ThreadTitleRegenerationService->>OrchestrationV2AppThread: Retrieve history through fork run
  OrchestrationV2AppThread-->>ThreadTitleRegenerationService: Return inherited history and ancestor title
  ThreadTitleRegenerationService->>generateThreadTitle: Pass forkSource
  generateThreadTitle->>buildThreadTitlePrompt: Pass forkSource

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Possibly related issues

• [Bug]: /compact as the first message in a forked thread fails with "Cannot compact an empty thread" #24160: The issue concerns /compact treating inherited fork history as empty. This PR also traverses inherited history, but uses it for title generation.

Possibly related PRs

• pingdotgg/t3code#23830: Both PRs change the thread-title generation pipeline and its generation input.
• pingdotgg/t3code#24172: Both PRs resolve history inherited through fork ancestry, for different operations.

Suggested reviewers: juliusmarminge, maria-rcks

Merge Risk: Minimal · up to eab78

The reviewed fork-title changes have no identified issue that needs resolution before merging.

Pre-merge checks: 3 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Description check		The description explains the problem, the implementation, and observed verification results. However, it does not use the required Problem, Change, Scope and approval, and Verification sections. It al…	Rewrite the description using all required template sections. Add the triaged issue or explicit maintainer approval with a link, identify the focused test and command, and state any checks that were not run.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: improving title generation for forked threads using inherited history.
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.

Full details: Description check

Explanation

The description explains the problem, the implementation, and observed verification results. However, it does not use the required Problem, Change, Scope and approval, and Verification sections. It also does not link a triaged issue or maintainer approval, and it omits the test name and command.

Resolution

Rewrite the description using all required template sections. Add the triaged issue or explicit maintainer approval with a link, identify the focused test and command, and state any checks that were not run.

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