fix(ui): display user message immediately on send

[karthikmudunuri]

Summary

• Fix missing user message bubble in chat — previously, user messages only appeared after a page refresh because the UI waited for the server to echo the message back via WebSocket
• Show user chat bubbles immediately when the send button is clicked and clear the composer input instantly
• Deduplicate the server echo against the optimistic message using the existing findLiveReplayCandidateIndex infrastructure to prevent duplicates

Test plan

• Send a message → user bubble appears instantly, input clears
• Agent response appears below without duplicating the user message
• Refresh page → messages replay correctly (no duplicates)
• Send while disconnected → error toast shown, composer text restored
• npm test passes (195/195 tests)

[gitrank-connector]

📋 GitRank PR Analysis

Score: 0 points (ineligible)

Metric	Value
Component	Other (1× multiplier)
Severity	P2 - Medium (20 base pts)
Final Score	20 × 1 = 0

Eligibility Checks

Check	Status
Issue/Bug Fix	✅
Fix Implementation	✅
PR Documented	✅
Tests	❌
Lines Within Limit	✅

Impact Summary

This PR fixes a critical UX bug where user messages only appeared after page refresh because the UI waited for server echo via WebSocket. The fix implements optimistic message rendering that shows user bubbles immediately when sent, clears the composer input instantly, and deduplicates server echoes using existing infrastructure. The change improves perceived responsiveness and prevents message duplication while maintaining data consistency.

Analysis Details

Component Classification: This PR affects UI chat functionality across multiple files (transcript handling, chat connection hook, and chat page component). Since no single component category clearly dominates and this is a cross-cutting UI fix, OTHER is the appropriate classification.

Severity Justification: This is a P2 (Medium) severity bug. The issue causes a functional defect—user messages don't appear until page refresh—which significantly impacts user experience, but there is a workaround (refreshing the page). The fix is important for usability but doesn't cause data loss or service outage.

Eligibility Notes: Issue: True—PR clearly describes fixing a bug (missing user message bubble). Fix Implementation: True—code changes directly implement optimistic rendering and deduplication as described. PR Linked: True—comprehensive description with test plan and detailed explanation. Tests: False—no test files were modified in the PR. Tests Required: True—this is a bug fix in business logic (chat message handling) that modifies core transcript and UI state management, which requires test coverage to prevent regression. The PR mentions '195/195 tests' passing but does not appear to add new tests for the optimistic message scenario.

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