Address #126 review: one home for the middleware rationale

The why-a-controller-can't-reach-the-socket story was told in full in
deadlines.go, agent.go, the test, and CLAUDE.md. It lives in deadlines.go
now; the others say what they need to and point there.

Co-Authored-By: Claude Fable 5 <[email protected]>

internal/api/sse_deadline_test.go

@@ -112,18 +112,12 @@ func TestEventStreamRefreshesDeadlinePerFrame(t *testing.T) {
 // production middleware stack — which is where it was still broken.
 //
 // The two tests above passed while the deployed instance cut every agent turn
-// at exactly 30s with "The connection dropped partway through." The difference
-// is the middleware: the logging middleware in New replaces c.Writer with a
-// wrapper that embeds the gin.ResponseWriter INTERFACE, which has no Unwrap. An
-// http.ResponseController built from the handler's c.Writer unwraps layer by
-// layer looking for SetWriteDeadline, can't see past that wrapper, and returns
-// ErrNotSupported — putting the stream back on the server's absolute
-// WriteTimeout. The first write past it fails, which cancels the request
-// context and closes the socket under the client mid-frame.
-//
-// So: the same scenario as the first test, hosted on the engine New builds, in
-// the order cmd/pansy runs it. Any future middleware that wraps the writer, or a
-// reorder that puts one ahead of the controller capture, fails here.
+// at exactly 30s: they host openEventStream on a bare engine, and it is the
+// logging middleware in New that hides the socket from a ResponseController
+// built in a handler (deadlines.go has the mechanism). So: the same scenario as
+// the first test, hosted on the engine New builds, in the order cmd/pansy runs
+// it. Any future middleware that wraps the writer, or a reorder that puts one
+// ahead of the controller capture, fails here.
 func TestEventStreamOutlivesWriteTimeoutBehindMiddleware(t *testing.T) {
 	got, err := streamFrames(t, authEngine(t, localCfg()), 300*time.Millisecond, 300*time.Millisecond, 3)
 	if err != nil {