fix(desktop): submit first message after session creation

[sidharthgehlot]

Summary

• allow the intentional new-chat draft promotion onto its newly created stored-session route
• keep session-isolation protection by validating the returned runtime ID and canonical route before continuing
• abort if the user genuinely switches chats during post-create async work
• add regression coverage for both the successful first-message flow and the late-switch race

Root cause

The submit pipeline pinned the new-chat route before session.create. Creation then correctly navigated to the new stored session, but the pipeline interpreted that expected route change as user-driven context drift, cancelled the first submission, and restored the text to the composer.

Test plan

• npx vitest run --environment jsdom src/app/session/hooks/use-prompt-actions/index.test.tsx (44 passed)
• npm run typecheck
• ESLint on the changed files (0 errors; one pre-existing padding warning in the test file)
• git diff --cached --check
• independent review of the final diff

[teknium1]

Thanks for the focused reproducer and race coverage. Current main already implements this first-message/new-chat drift fix, so this PR is redundant.

• Automated hermes-sweeper review verified 8c288760d0b50107e608ed42df81f48c7ccedde5 (fix(desktop): stop the submit drift guard from aborting every new chat) is on main.
• apps/desktop/src/app/session/hooks/use-prompt-actions/submit.ts:301 now validates the created runtime session via activeSessionIdRef, then re-pins the stored-session and route baselines at lines 313–316 before submission continues.
• apps/desktop/src/app/session/hooks/use-prompt-actions/index.test.tsx:1527–1557 covers the promoted new-chat route and asserts prompt.submit uses the created runtime session; the adjacent test covers the late-switch abort.
• The timeline's bug(desktop): first message in a new session leaves a blank session — no messages, no error, no response #63078 cross-reference also describes broader backend and churn scenarios; those are separate from the exact first-message guarantee implemented here.