fast-qa: SSE streaming execution to fix Vercel timeout + bug fixes

[causehacker]

Summary

Rearchitects Fast QA's test execution to use SSE streaming, fixing 504 Gateway Timeout errors on Vercel's free tier.

Changes

New: /api/execute-test (SSE streaming)

• Executes a single test case against Mino and streams events back to the client in real-time
• Edge Runtime with text/event-stream response - keeps connection alive, no timeout
• Events: test_start, streaming_url, step_progress, test_complete, test_error
• API key stays server-side (client never sees MINO_API_KEY)

Updated: useTestExecution hook

• Consumes SSE streams instead of blocking JSON responses
• Client-side parallelism (3 concurrent tests by default)
• Real-time step-by-step progress updates in the UI
• Same external API - no component changes needed

Bug fixes

• gpt-5-nano → gpt-4.1-nano: Reasoning models return empty content field, breaking AI SDK's generateText
• generate-report type error: extractedData wasn't being parsed correctly
• Frontend data key mismatch: API returns testCases but frontend expected tests

Deprecated

• /api/execute-tests (plural) marked deprecated - blocks until all tests complete, causing 504s on Vercel free tier (30s edge limit)

Problem

The original /api/execute-tests endpoint runs all tests server-side, consuming Mino's SSE stream internally. Mino browser automation typically takes 30-90s per test, exceeding Vercel's free tier edge timeout (30s).

Solution

Move SSE consumption to the client by streaming Mino events through the edge function. Edge functions can stream responses indefinitely as long as data flows, sidestepping the execution timeout.

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[causehacker]

We were deploying Fast QA on Vercel's free tier and ran into 504 timeouts - Mino automation typically takes 30-90s which exceeds the 30s edge function limit.

Rearchitected test execution to stream Mino's SSE events through the edge function to the client, which keeps the connection alive and has the nice side effect of giving users real-time step progress. Also fixed a few bugs we hit along the way (gpt-5-nano returns empty content on reasoning models, type error in report generation, and a testCases vs tests key mismatch in the frontend).

Ran a bunch of tests and all came back healthy, hope this helps!