PR writer model names itself in attribution footers because it never receives the thread's model and harness #26892

What happened

My project's AGENTS.md has a rule: agent-written PR descriptions end with a footer naming the model and harness that did the work (*Model: <model> · Harness: <harness>*).

I do the coding in threads running Claude Opus (claude-opus-5-5, Claude harness). I set a different, cheaper model as the source control writer (currently codex / gpt-6.1-terra). When I create the PR with T3's built-in Create PR action, the footer names the writer model (Model: GPT-6 · Harness: Codex) instead of the model that did the work. It happens every time. Earlier, with claude-haiku-5-5 as the writer, the footer said Haiku.

Diagnosis

The writer model never receives the thread's model or harness, so it can only describe itself.

• buildPrContentPrompt (packages/provider-core/src/server/textGenerationPrompts.ts) builds the prompt from the diff, the commits, the repo PR template and an optional threadContext.
• threadContext comes from readThreadContext (apps/server/src/git/GitManager.ts:690). That function renders only the thread's visible message history. It never includes the thread's modelSelection (instance and model), even though the thread projection stores it.
• The writer CLI runs with the repo as its working directory (cwd in CodexTextGeneration.ts / ClaudeTextGeneration.ts), so it loads the repo's AGENTS.md / CLAUDE.md. It applies any attribution rule there using its own identity, because it has no other identity to use.
• The custom PR instructions setting (style.customInstructions, passed as changeRequestInstructions) is fixed text, so it can't carry a different model for each thread.
• Current main builds the prompt the same way.

Proposed fix: add the producing thread's model and harness to the PR prompt (and the commit message prompt, when generated from a thread) as labelled reference data, for example "Change produced by: model claude-opus-5-5, harness Claude". The writer can then fill in attribution footers correctly, and it doesn't present itself as the author.

Steps to reproduce

1. In a repo, add to AGENTS.md: "End PR descriptions with *Model: <actual model> · Harness: <actual harness>*, read from the running session."
2. In T3 Code settings, set the source control writer model to a different provider and model than the coding thread (e.g. writer codex / gpt-6.1-terra, thread claudeAgent / claude-opus-5-5).
3. In a worktree thread on Opus, make a change and commit it.
4. Use T3's Create PR action for that thread.
5. Expected: footer names claude-opus-5-5 / Claude. Actual: footer names the writer (GPT-6 / Codex).

Version

0.1.5-nightly.20261029.3867 (desktop app + local server)

Environment

Linux x64 (Omarchy, kernel 7.2.8), Node 26.12.1, codex-cli 0.165.0, Claude Code 2.1.312

Evidence

# Thread that produced the PR (thread projection, read-only)
modelSelection: { instanceId: "claudeAgent", model: "claude-opus-5-5" }
pullRequests[0]: { number: 461, source: "created", headBranch: "t3/a6f47597" }

# settings.json
sourceControlWriterModelSelection: { instanceId: "codex", model: "gpt-6.1-terra", reasoningEffort: "medium" }

# Footer the writer put in the PR body
*Model: GPT-6 · Harness: Codex*

Related issues

None found. Searched for attribution, PR writer model, source control writer and PR description model name. #11077 (MR text leaking data from other threads) also concerns threadContext, but about the opposite problem.

Fix applied or workaround

Nothing applied. Workarounds: have the coding agent open the PR itself (gh pr create) instead of using Create PR, or change the repo rule so a writer that didn't make the change writes unknown.

Filed by

Claude Code (claude-opus-5-5) via t3 triage