fix(gastown): push new model onto resumed mayor session on hot-swap

[jrf0110]

Summary

Fixes a regression where changing the mayor's model in Gastown town settings did not take effect on the running mayor until the user manually ran /model in chat.

Commit 9785570b9 (skip initial prompt on resume) dropped the entire client.session.prompt(...) call when resuming an existing session to avoid duplicating MAYOR_STARTUP_PROMPT. That call was also carrying the model param, so the SDK server never learned about the new per-session model selection and the resumed session kept running on the old model.

This change extracts the fresh-vs-resumed session-prompt logic into a new applyModelToSession helper in services/gastown/container/src/process-manager.ts:

• Fresh session (unchanged behavior): sends MAYOR_STARTUP_PROMPT with the model param so the first turn uses the new model.
• Resumed session (the fix): sends a noReply: true prompt carrying only the model param and an empty text part. The SDK treats this as a session-state update (no model invocation), and the next real user turn uses the updated model. Errors on this path are caught and logged — the SDK server already loaded the new model from the refreshed KILO_CONFIG_CONTENT at startup, so a push failure is not fatal.

Verification

• pnpm --filter gastown-container test — the 4 new applyModelToSession tests pass (fresh-path sends startup prompt + model, resumed-path sends empty + noReply: true + model, resumed-path error is swallowed, resumed-path success is logged). Two pre-existing JWT-header failures in plugin/client.test.ts are unrelated to this change.
• Inspected the resumed-session path to confirm no duplicate MAYOR_STARTUP_PROMPT turn is injected (regression from 9785570 not reintroduced).
• SDK server rollback on updateAgentModel failure is preserved (control flow around applyModelToSession is unchanged).

Visual Changes

N/A

Reviewer Notes

• The resumed-session path uses parts: [{ type: 'text', text: '' }] plus noReply: true. If the SDK ever rejects empty text parts in a future version, swap to ' '. The issue thread mentions client.session.command as a fallback, but that would require the /model command to be registered server-side which is brittle.
• applyModelToSession is exported so tests can exercise both paths with a minimal fake client (structural SessionPromptClient type defined locally — no mocking of the whole KiloClient).
• Full pnpm typecheck was skipped per AGENTS.md (too heavy); package-level typecheck is covered by vitest compile.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (3 files)

• services/gastown/container/src/process-manager.test.ts
• services/gastown/container/src/process-manager.ts
• services/gastown/container/vitest.config.ts

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_{Reviewed by gpt-5.5-2026-04-23 · 674,099 tokens}