fix: log SSE payload parse failures instead of silently swallowing them

[omoh5]

Summary

Restores observability into a currently invisible failure mode by logging malformed SSE payloads instead of silently discarding them.

Problem

useStreamEvents.ts:96-106 — the handleEvent callback swallows any JSON.parse failure with an empty catch block and no logging:

} catch {
  // Silently ignore malformed event messages
}

This means a corrupted or unexpected SSE frame vanishes without a trace. In a financial application where real-time stream events drive UI state (claimable amounts, status badges, action buttons), silently dropping events can lead to confusing user-facing behavior with zero diagnostic trail.

Solution

1. Import logger from @/lib/logger — consistent with the codebase convention used in useTokenPrice.ts and useIncomingStreams.ts.

2. Log the parse failure with structured context in the catch block:

   • type — which SSE event type failed to parse
   • raw — the raw payload string for debugging
   • error — the caught parse error

3. Added emitRaw() to MockEventSource — test helper that fires a named event with a raw (non-JSON) string payload, enabling malformed-payload testing.

4. New test: "logs a parse error when SSE payload is malformed" — verifies that:

   • console.error is called (logger.error always surfaces, even in production)
   • The log message contains "SSE payload parse failure"
   • The raw malformed payload appears in the logged arguments
   • The malformed event does NOT appear in the events array

Files Changed

File	Change
frontend/src/hooks/useStreamEvents.ts	Import logger, replace empty catch with structured error logging
frontend/src/__tests__/useStreamEvents.test.tsx	Add emitRaw() to MockEventSource, add malformed-payload test

Test Results

All 15 tests pass (14 existing + 1 new):

✓ src/__tests__/useStreamEvents.test.tsx (15 tests) 99ms

Closes #1210

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Co-Authored-By: Codebuff noreply@codebuff.com