http.Server.WriteTimeout is an ABSOLUTE deadline from when the request header
was read, not an idle timeout. pansy sets it to 30s (cmd/pansy/main.go:65)
while an agent turn is budgeted 4 minutes, so every turn over 30 seconds was
cut mid-stream. The 4-minute runTimeout was unreachable; the real ceiling was
30 seconds.

That also meant the keep-alive added in #73 could never do its job. It ticks
at 20s, so it got exactly one tick before the connection it was pacing was
destroyed underneath it — a mechanism built to survive long silences that was
structurally incapable of surviving them.

The failure is invisible from the handler: writes made after the deadline
return err == nil and their bytes are discarded. There is no error to check
and none to log, which is why this survived a review that specifically looked
at the discarded write error. Only the client sees it, as an unexpected EOF,
which web/src/lib/agent.ts reports as "The connection dropped partway
through." — indistinguishable from a real network fault.

Because it is invisible server-side, the test drives a real http.Server with a
short WriteTimeout and asserts from the CLIENT side. Against the unfixed code
it gets 1 of 4 frames and an unexpected EOF; a test that inspected the return
of io.WriteString would have passed against the bug.

gin 1.10.1's responseWriter implements Unwrap, so ResponseController reaches
the underlying conn. A failure to clear the deadline IS worth logging: it
means the stream will be cut and we cannot prevent it.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

@@ -0,0 +17,4 @@
+// once it passes, however recently the handler wrote. pansy sets it to 30s while
+// an agent turn may run for minutes.
+//
+// This has to be driven through a real http.Server and asserted from the CLIENT