fix(frontend): preserve composer drafts across remounts

[Alphaxiaoteng]

Summary

• keep the composer draft in one bounded Recoil record so the WelcomeScreen → Footer owner swap cannot discard in-progress input
• make Input controlled by that single source of truth while preserving reset, command, favorite, and URL-prompt behavior
• discard the old draft at session boundaries and track URL-prompt initialization so a remount cannot restore a prompt the user edited or deleted
• fixes Composer remounts whenever the message list transitions empty↔non-empty, dropping in-progress input #3022

Regression evidence

With the new owner-swap test kept in place and the composer temporarily restored to local state, the test failed as expected:

Expected the element to have value: draft message
Received:

The URL-prompt boundary also failed before its guard was added:

Expected: edited draft
Received: initial prompt

The first bounded-state revision also proved that merely hiding a stale session record was insufficient: switching a → b → a restored draft message. The final implementation clears that single record when the session changes.

Verification

• pnpm --filter @chainlit/app test -- tests/MessageComposer.spec.tsx — 4 passed
• pnpm --filter @chainlit/app test — 6 files, 36 tests passed
• pnpm type-check — frontend and react-client passed; copilot reports its repository-configured skip
• pnpm lint and pnpm lint:fix — passed
• pnpm format-check and pnpm format — passed
• pnpm build — react-client, frontend, and copilot production builds passed
• git diff --check — passed

Prior work and AI assistance

PR #3028 previously explored the same session-scoped state direction and was closed by its author before maintainer review. Thank you to @Iams4kura for that public investigation. This PR independently re-ran the baseline, adds explicit owner-level, session-lifecycle, and URL-prompt regressions, and follows this repository's required AI attribution. OpenAI Codex assisted with implementation and review; both commits include the required Co-Authored-By trailer.

[cubic-dev-ai]

1 issue found across 4 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="frontend/tests/MessageComposer.spec.tsx">

<violation number="1" location="frontend/tests/MessageComposer.spec.tsx:143">
P3: The session-isolation test only checks that a new session shows an empty draft; it never switches back to session 'a' to confirm the original draft is still retained. Since the PR's stated goal is to "isolate drafts between sessions" (each session keeps its own draft), a regression that clears the draft globally on session change would pass this test. Add a follow-up assertion that rerendering with sessionId 'a' restores 'draft message'.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P3: The session-isolation test only checks that a new session shows an empty draft; it never switches back to session 'a' to confirm the original draft is still retained. Since the PR's stated goal is to "isolate drafts between sessions" (each session keeps its own draft), a regression that clears the draft globally on session change would pass this test. Add a follow-up assertion that rerendering with sessionId 'a' restores 'draft message'.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At frontend/tests/MessageComposer.spec.tsx, line 143:

<comment>The session-isolation test only checks that a new session shows an empty draft; it never switches back to session 'a' to confirm the original draft is still retained. Since the PR's stated goal is to "isolate drafts between sessions" (each session keeps its own draft), a regression that clears the draft globally on session change would pass this test. Add a follow-up assertion that rerendering with sessionId 'a' restores 'draft message'.</comment>

<file context>
@@ -0,0 +1,172 @@
+    });
+    view.rerender(<ComposerOwners sessionId="b" />);
+
+    await waitFor(() => {
+      expect(screen.getByRole('textbox')).toHaveValue('');
+    });
</file context>

[Alphaxiaoteng]

Addressed the review in 89b1968:

• Replaced the atomFamily with one bounded active-session draft record, and clear that record when sessionId changes, so Recoil cannot accumulate one atom per conversation.
• Moved URL-prompt initialization state into the same record. A user-edited or explicitly deleted prompt now stays edited/deleted across the WelcomeScreen → Footer remount.
• Clarified the session-boundary contract: drafts are intentionally discarded when the session changes rather than retained for later restoration. The regression now exercises a → b → a and expects the old draft to remain discarded.

Reverified on the new head: focused composer tests 4/4, full frontend suite 36/36, type-check, lint, Prettier, complete recursive production build, and git diff --check all passed.