[Feature]: Reference an existing thread as context in another conversation

[Aneaire]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/desktop

Problem or use case

Context

I use T3 Code to run agents that sometimes execute with custom skills or configuration. When an agent does something unexpected — for example, a custom skill steers the AI the wrong way during a test run — I want to have another AI review that conversation to figure out what went wrong and propose a fix to the skill.

The problem

Today there is no way to point one conversation at another:

• I have to manually copy and paste the transcript into a new thread.
• Copy/paste drops tool calls, reasoning output, diffs, and other structured context.
• Large threads are impractical to reproduce manually, and retyping loses fidelity.

What I'm trying to do

• Run an analysis thread that references an earlier conversation.

• Ask the new agent questions about that conversation, such as:

  "Analyze the transcript of thread X and tell me why my skill misbehaved, then propose a fix to the skill file."

• Keep the referenced thread read-only; the analysis happens in the new conversation.

Why it's hard today

There is no built-in way to attach a thread as context, so this workflow is slow, lossy, and error-prone.

Proposed solution

Add a way to reference an existing thread from within another conversation:

• "Reference thread" action on a thread (sidebar / thread menu) that lets you pick it as context, or an @reference-style mention in the composer that resolves to a saved thread.
• When a thread is referenced, the new conversation receives that thread's transcript as read-only context (user + assistant messages, and where available tool calls and reasoning).
• The referenced thread stays untouched — analysis and follow-up happen only in the referencing conversation.
• The UI shows a clear "Referenced: " chip in the composer so you can see what context will be sent before you send.

A pragmatic v1: attach the transcript as structured context on thread.turn.start (extending ChatAttachment or adding a referencedThread field), letting the provider see it as additional context for that turn.

Why this matters

• Lets a different model/agent review what happened in a past run — e.g. diagnosing why a custom skill misbehaved and proposing a fix to the skill — without manual copy/paste.
• Copy/paste today loses tool calls, reasoning, diffs, and timestamps, so the reviewing AI works from incomplete information.
• Unlocks retrospective workflows: audit a conversation, review agent behavior after the fact, and iterate on skills/prompts based on full evidence rather than a pasted summary.
• The workflow is impossible today, so this is net-new capability rather than a polish improvement.

Smallest useful scope

A first pass only needs to:

• Allow referencing one existing thread from a new conversation.
• Inject that thread's transcript (user + assistant text) into the referencing conversation's first turn as context.
• Render a small "Referenced thread" indicator so the user knows context was attached.

No cross-thread linking UI, no live updates from the referenced thread, no graph/visualization, and no multi-thread references.

Alternatives considered

No response

Risks or tradeoffs

No response

Examples or references

No response

Contribution

• I would be open to helping implement this.