Two related fixes after re-testing on the deploy preview:
1. SEGMENT_BUDGET_MS: 54_000 -> 40_000.
Empirically, Netlify Edge Function responses get cut anywhere
between ~49 s and ~60 s wall-clock — significantly more variance
than the docs imply. With a 54 s budget, our segment_end write +
controller.close() sometimes lands AFTER the platform has already
killed the response (curl: 'HTTP/2 stream 1 was not closed cleanly
before end of the underlying stream'). 40 s gives ~10 s of headroom
on the low end of the observed range while still keeping segment
overhead reasonable (~1 segment per 40 s of brief).
2. HEARTBEAT_MS: 10_000 -> 5_000.
Tighter keep-alive so the connection stays warm even during long
model-thinking gaps where the agent isn't emitting events.
3. Drop the 'await upstream.cancel()' between backfill and tail.
The upstream fetch's body is already cleaned up by
segmentAbort.abort() (or will be by the runtime once we drop our
reference). On Deno Edge, awaiting cancel() on an already-aborted
body can hang, which prevents segment_end from being written.
Co-Authored-By: alex <alex@semipublic.co>
Devin AI
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