fix(core): preserve session state on abort and error / session expiration (replaces #1055)

[Utkarsh-X]

Fixes #1054
Reopens #1055 (rebased onto the new main history following @victorxheng's note).

What this fixes

When a user interrupts a run with Esc or when a session expires, sending a follow-up message immediately was reading a stale/null in-memory previousRunStateRef. This caused the SDK to construct a fresh empty session state (messageHistory = []), wiping conversation context.

What's included (addressing the #1055 review feedback)

1. Regression tests (send-message.test.ts): Added 3 dedicated tests verifying:
   • User abort (Esc) preserves turn history + tool calls in createRunConfig.previousRun.
   • Session expiration / gate errors preserve history on "continue".
   • Mid-run chat switches (runChatIsCurrent === false) never leak state into other chats.
2. DRY state sync (use-send-message.ts): Consolidated the assignment into a simple 5-line syncRunState closure used uniformly across abort, completion, and error handlers.
3. Clean scope: Reverted the previous prompt text tweaks so this PR is strictly isolated to the session state bug (3 files total).
4. Re-render safety: Checked store subscriptions — zero React components subscribe to state.runState, so updating it alongside streamStatus = 'idle' causes no visual layout flash.

I intentionally kept this as minimal and safe as possible to solve the demonstrated bug without bloating the change surface or touching unrelated client/storage APIs. That said, if you'd prefer any tweaks or want me to look into anything further here, just let me know and I'm happy to research and adjust!

Verification

• Test Suites (202 / 202 passed across touched areas):
  • bun test cli/src/hooks/helpers/__tests__/send-message.test.ts (49 passed, including the 3 new regression tests)
  • bun test sdk/src/__tests__/run-cancellation.test.ts (16 passed)
  • bun test cli/src/utils/__tests__/run-state-storage.test.ts (37 passed)
  • bun test packages/agent-runtime/src/__tests__/compact-history.test.ts (31 passed)
  • bun test agents/__tests__/context-pruner.test.ts (69 passed)
• Builds:
  • bun run build:sdk (ESM, CJS, and TypeScript declarations bundled with 0 errors)
  • bun run build:freebuff (Native executable built with exit code 0)