[lucasr1b]

Summary

picking a model from another provider in the composer (say gpt to claude) wiped whatever you had typed in the prompt.

that pick is a harness switch, so acpmux starts a new session. the composer keeps drafts per session, and when its sessionId changed it swapped in the new session's saved draft, which is empty for a brand new session. the old chat is also hidden while the new one starts, so the id goes old -> none -> new and each step cleared the text.

now the pane passes switching (a harness switch intent is live) to the composer. during a switch the typed prompt stays and becomes the new session's draft (the existing hydrate path then writes it durably). moving to another chat still shows that chat's own draft, same as before.

same-provider model picks never changed the session, so they weren't affected.

Testing

• added webviews/test/composer-switch-keeps-draft.test.tsx: a switch (session a -> none -> b) keeps the prompt, and moving to another chat still shows that chat's draft.
• red then green with the same command, bun test test/composer-switch-keeps-draft.test.tsx: on the test commit 9bfc08786a7 1 fail (prompt came back ""), with the fix 2 pass.
• ran every draft / composer / harness switch / model picker test file (45 files), all pass. bun run typecheck clean, oxlint clean on the touched files.
• checked live in a tagged dev build: typed a prompt, picked another provider's model, the text stayed.

Changelog

Fixed: Picking a model from another provider no longer clears the prompt you were typing

Proof

behavior fix in the composer, covered by the test above; checked live in a tagged build.

Checklist

• Behavior changes have added or updated tests, or Testing says why not
• Reviewed with a subagent before merge (cmux-review), and all bot and human review comments resolved

---

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---

Summary by cubic

Fixes the composer clearing the typed prompt when picking a model from another provider (say switching from gpt to claude).

Picking another provider's model is a harness switch that starts a new session. The composer keeps drafts per session, so when the session changed it swapped in the new session's empty draft. The pane now passes a switching flag while the harness switch is underway: the typed prompt stays and becomes the new session's draft. A chat's own saved draft wins over a carried prompt, so moving to another chat mid-switch still shows that chat's draft, as before.

^{Written for commit e086207. Summary will update on new commits.}

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[github-actions]

Receipt for e086207 (this PR's head; a new push replaces it)

• Visual review: HQ feed card · gallery before/after runs
• Checks: this head
• App of this head (app.zip, kept 1 day): gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr21937 -f ref=composer-switch-keeps-draft -f platform=macos -f backend_mode=local

[teamleaderleo]

Bead cx-bktsu created for this PR by the cmux coordinator.

[lucasr1b]

review (claude subagent, correctness first) on head 73c7d84b440, base c77b58ee93e, pr #21937, owner lucasr1b.

no p0 / p1. verified: during a shown switch the composer sees old -> "" -> new and switchView.intent is set at every render of it (leave() and changed() land in one render; attach() emits before the intent clears in run()); cancel paths (chat.select, chat.new, fork, editResend, handoff.prepare) clear the intent a commit before the session moves; the carried text reaches the new session's durable draft through the existing hydrate branch; the old chat keeping its copy is fine (it's the only copy if a switch fails). new tab deferred picks (undefined -> "") were also wiping the text and are covered now.

findings and resolution:

• p2: a pending, not yet shown switch plus a session change through a path that skips cancel() (chat.adoptLive, chat.offer.open fallback, chat.handoff.start/discard) could let the carried prompt replace that chat's own saved draft. fixed in e086207: a chat's saved draft now wins (restored || carried || draft); carried text only fills a session with no draft, which a switch's new session always is. new test "moving to a chat with its own draft mid-switch keeps that chat's draft" fails on the old ordering and passes now.
• p2: test used undefined where the app passes "" and missed the leak / same-batch cases. fixed in e086207: uses "", adds settle-then-navigate (expects "") and intent-clears-in-the-same-render (expects the prompt kept).
• p2, already on feat-cmux-next: prompts handed back by a failed/cancelled switch go into the "" session and are lost if the user then moves to another chat. not changed here, separate fix.

after the fixes on e086207: bun test test/composer-switch-keeps-draft.test.tsx 4 pass; all 45 draft / composer / harness switch / model picker test files pass; bun run typecheck clean; oxlint clean on touched files.

[blacksmith-sh]

Found 2 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmphjpyy69m/summary-missing.json (live):/summary-missing.json (live):	View Logs
/tmp/tmpwbcg3ad0/summary-fail.json (live):/summary-fail.json (live):	View Logs

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