Fix race condition blocking multi-turn chat conversations

[Copilot]

Problem

Dashboard chat accepted the first message but silently ignored follow-ups, breaking multi-turn conversations. Root cause: sendMessage checked React state to guard against duplicate sends, but state lagged storage updates by up to 400ms (the polling interval).

Changes

Query storage directly instead of stale React state:

// Before: Race condition when messages sent < 400ms after completion
const threadFromStorage = threads.find(t => t.id === targetThreadId);

// After: Always check source of truth
const threadFromStorage = await threadStore.getById(targetThreadId);

Removed threads dependency from useCallback since we no longer read from React state for the streaming check.

Technical Details

The flow that caused the bug:

1. Message completes → executeChatResponse writes isStreaming: false to storage
2. User sends follow-up before polling refreshes React state
3. Check sees stale isStreaming: true → message silently dropped

Storage queries bypass the stale state issue entirely while maintaining the duplicate-send protection.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Bug: Dashboard chat only works for single turn (follow-ups don't trigger AI)</issue_title>
<issue_description>## Description
During livestream testing, discovered that the chat experience on the dashboard only works for the initial message. Follow-up messages don't trigger the AI to respond.

Steps to Reproduce

1. Navigate to dashboard
2. Send initial chat message
3. AI responds successfully
4. Send follow-up message
5. AI does not respond

Expected Behavior

Chat should support multi-turn conversations where follow-up messages trigger AI responses.

Actual Behavior

Only the first message gets a response. Subsequent messages are ignored.

Impact

• Users cannot have ongoing conversations
• Limits chat usefulness to single Q&A exchanges</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Bug: Dashboard chat only works for single turn (follow-ups don't trigger AI) #8

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[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None