Generate system instructions from chat history

[gyanu2507]

Fixes #357

System instructions currently have to be written from scratch, even when the chat already made it obvious how the user wants the agent to behave.

This adds a From chat button on the session header. It drafts instructions from the transcript, you can edit them in a dialog, and nothing is saved until you apply. Inline chats can apply the draft to that session. Named/registry agents only get copy, so we don't mutate the saved agent.

Short chats return 422 before we call the model, so a "hey"/"hi" conversation doesn't turn into a generic helpful-assistant prompt.

New route: POST /api/v1/sessions/{session_id}/generate-instructions

It only returns a suggestion (instructions, current_instructions, sources). Saving still goes through the existing session update.

I didn't regenerate the SDK. The UI adapter hits the new path with client.fetch.

---

Note

Medium Risk
New authenticated session endpoint invokes the session model on transcript data and updates agent specs on apply; mistakes could affect future turns, though drafts are explicit and short chats are gated.

Overview
Adds From chat in the session header so users can infer system instructions from the transcript, edit them in a modal, and only persist when they choose Apply (inline/mutable sessions). Named registry-bound chats get Copy only so saved agents are not mutated server-side.

Backend exposes POST /api/v1/sessions/{session_id}/generate-instructions, which returns a draft (instructions, current_instructions, sources) without writing the session. Transcript extraction skips subagent threads; 422 is returned when user text is too thin before any LLM call, and model output is filtered to block generic one-liners. The harness UI adapter calls the new route via client.fetch; saving still uses the existing session update path after flush/adopt.

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🦋 Changeset detected

Latest commit: 243929c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@truefoundry/trueforge	Patch
@truefoundry/trueforge-ui	Patch
frontend	Patch

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