Add basic thread forking from the sidebar by colonelpanic8 · Pull Request #4390 · pingdotgg/t3code

colonelpanic8 · 2026-07-23T19:37:34Z

What Changed

adds a provider-aware thread.fork orchestration command and persists fork lineage
adds Fork thread to the web/desktop sidebar thread context menu
clones the conversation through its latest completed assistant turn, then opens the fork as a normal full thread
supports native forking for Codex, Claude, and OpenCode
removes the response-level fork controls and fork-to-side-panel UI

Why

The basic fork interaction should feel like cloning a thread: right-click it in the sidebar, fork it, and continue in an independent copy. Branching from an older response can be added later, but it should not complicate the first version or introduce a separate side-chat surface.

UI Changes

Right-click a supported thread in the sidebar and select Fork thread. The action is disabled while the latest turn is running or before the thread has a completed assistant response. A successful fork appears as <original title> (fork) and opens in the normal full-thread route.

There is no split view, embedded side chat, or per-response fork button.

Checklist

focused server, contracts, client-runtime, and web tests pass (326 tests)
affected server, contracts, client-runtime, and web typechecks pass
targeted formatting and lint checks pass
refreshed UI capture (the collaborative preview automation failed to attach to the isolated test app)

Note

Add thread forking from the sidebar and assistant message timeline

Adds a 'Fork thread' context menu item in both sidebar variants and a per-message fork button in the assistant timeline; both are gated on provider fork capability (codex, claudeAgent, opencode).
Introduces a thread.fork command and thread.forked event in the contracts layer; the decider clones messages up to the specified source turn (excluding streaming messages), rewrites attachment ids, and records fork lineage.
The Claude, Codex, and OpenCode provider adapters each implement native session forking (sessionFork: "native"), forwarding fork context to their respective SDKs.
The projection pipeline persists fork lineage columns (forked_from_thread_id, forked_from_turn_id) via migration 035, inherits messages from the source thread, and physically copies attachment files into fork-owned paths post-transaction.
The projector removes the MAX_THREAD_MESSAGES cap, so threads now retain an unbounded message history.
Risk: Removing the message cap is a behavioral change that may increase memory and storage usage for long-lived threads.

^{Macroscope summarized b779c54.}

Note

High Risk
Touches orchestration, durable projections, attachment lifecycle, and provider session start/fork paths; unbounded message retention may increase memory and storage for long threads.

Overview
Adds end-to-end thread forking: a thread.fork command emits thread.forked with inherited history through a chosen completed turn, fork lineage on threads, and fork-owned message/attachment ids (createForkedAttachmentId). The SQL projection copies attachment files on fork, keeps inherited :fork: messages across revert, and migration 035 stores forked_from_* columns.

Provider integration — Codex, Claude, and OpenCode declare sessionFork: "native" and receive forkFrom (turn index/id + source resume cursor) when a forked thread starts; ProviderCommandReactor walks nested fork lineage to the provider-owning ancestor. getCommandReadModel now loads full per-thread message history (not capped like shell snapshots).

Client — @t3tools/client-runtime/thread-forking gates fork UI; sidebar Fork thread and chat Fork from this response call useForkThread / threadEnvironment.fork. In-memory projection drops the 2,000-message cap so command/read models can retain complete history.

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coderabbitai · 2026-07-23T19:37:42Z

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macroscopeapp · 2026-07-23T19:41:29Z

Approvability

Verdict: Needs human review

This PR introduces a new thread forking feature with substantial scope: new database schema, new event/command types, provider API integrations for Codex/Claude/OpenCode, and new UI components in sidebar and chat view. New user-facing capabilities of this magnitude warrant human review.

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cursor

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

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cursor · 2026-07-25T03:26:42Z

                isRevertingCheckpoint={isRevertingCheckpoint}
+                {...(isServerThread && supportsSelectedResponseFork(activeProviderStatus?.driver)
+                  ? { onForkFromResponse, isForkingResponse }
+                  : {})}


Timeline fork uses composer provider

Medium Severity

Per-message fork actions are gated on activeProviderStatus?.driver, which follows the thread composer’s selected provider instance before the thread’s session or model binding. Sidebar fork uses the thread’s provider instance instead, so the timeline can hide fork on supported threads or show it when native fork will fail.

^{Reviewed by Cursor Bugbot for commit b779c54. Configure here.}

…ted response from the sidebar) # Conflicts: # apps/web/src/components/Sidebar.tsx

github-actions Bot added vouch:unvouched PR author is not yet trusted in the VOUCHED list. size:XL 500-999 changed lines (additions + deletions). labels Jul 23, 2026

cursor Bot reviewed Jul 23, 2026

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Comment thread apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

Comment thread apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

Comment thread apps/server/src/orchestration/Layers/ProjectionSnapshotQuery.ts

macroscopeapp Bot reviewed Jul 23, 2026

View reviewed changes

Comment thread apps/server/src/orchestration/Layers/ProjectionPipeline.ts

Comment thread apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

Comment thread apps/server/src/orchestration/Layers/ProjectionPipeline.ts

colonelpanic8 force-pushed the t3code/add-thread-forking branch from 29c1ba0 to bf7ab07 Compare July 23, 2026 20:32

github-actions Bot added size:XXL 1,000+ changed lines (additions + deletions). and removed size:XL 500-999 changed lines (additions + deletions). labels Jul 23, 2026

macroscopeapp Bot reviewed Jul 23, 2026

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cursor Bot reviewed Jul 23, 2026

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Comment thread apps/server/src/provider/Layers/CodexSessionRuntime.ts

Comment thread apps/server/src/provider/Layers/ProviderService.ts

colonelpanic8 force-pushed the t3code/add-thread-forking branch 2 times, most recently from ac92627 to eb09585 Compare July 23, 2026 21:00

cursor Bot reviewed Jul 23, 2026

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Comment thread apps/web/src/components/ChatView.tsx Outdated

Comment thread apps/server/src/orchestration/decider.ts

Comment thread apps/server/src/orchestration/decider.ts

Comment thread apps/server/src/orchestration/projector.ts

colonelpanic8 force-pushed the t3code/add-thread-forking branch 2 times, most recently from 2e90fb7 to 3360755 Compare July 23, 2026 22:28

cursor Bot reviewed Jul 23, 2026

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Comment thread apps/server/src/orchestration/decider.ts

colonelpanic8 force-pushed the t3code/add-thread-forking branch 2 times, most recently from 0ae7550 to 0258dca Compare July 24, 2026 01:50

cursor Bot reviewed Jul 24, 2026

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Comment thread apps/server/src/orchestration/Layers/ProjectionSnapshotQuery.ts

colonelpanic8 changed the title ~~Add thread forking across web and mobile~~ Add basic thread forking from the sidebar Jul 24, 2026

cursor Bot reviewed Jul 24, 2026

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Comment thread apps/web/src/components/Sidebar.tsx

colonelpanic8 force-pushed the t3code/add-thread-forking branch 2 times, most recently from b9b18e0 to f4474ea Compare July 24, 2026 06:13

cursor Bot reviewed Jul 24, 2026

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Comment thread apps/web/src/hooks/useForkThread.ts Outdated

colonelpanic8 force-pushed the t3code/add-thread-forking branch 2 times, most recently from 9ac81ba to ece3d88 Compare July 25, 2026 00:01

nassimna and others added 3 commits July 24, 2026 20:19

feat: fork from a selected assistant response

b80d8d9

feat(mobile): fork from assistant responses

24f4453

fix: preserve fork history across providers and restarts

4307988

colonelpanic8 and others added 7 commits July 24, 2026 20:19

fix: harden nested thread forks

db2a4f3

fix remaining thread fork races and history gaps

5fc1c36

fix: reject forks from deleted threads

6172372

Simplify thread forking to sidebar cloning

40d3a04

Fix thread fork reactor test lint

4388b29

fix(web): preserve selected response fork points

f8b68a4

fix(web): share fork action lock globally

b779c54

colonelpanic8 force-pushed the t3code/add-thread-forking branch from ece3d88 to b779c54 Compare July 25, 2026 03:23

cursor Bot reviewed Jul 25, 2026

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colonelpanic8 added a commit to colonelpanic8/t3code that referenced this pull request Jul 25, 2026

stack: merge pingdotgg#4390 (Clone a thread through its latest comple…

37abf6f

…ted response from the sidebar) # Conflicts: # apps/web/src/components/Sidebar.tsx

colonelpanic8 added a commit to colonelpanic8/t3code that referenced this pull request Jul 25, 2026

stack: merge pingdotgg#4390 (Clone a thread through its latest comple…

9e3769a

…ted response from the sidebar) # Conflicts: # apps/web/src/components/Sidebar.tsx

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What Changed

Why

UI Changes

Checklist

Add thread forking from the sidebar and assistant message timeline

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Timeline fork uses composer provider

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colonelpanic8 commented Jul 23, 2026 •

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