From 3470aa658e5927118b433016cad2d36535afdfdc Mon Sep 17 00:00:00 2001
From: Rach Pradhan <54503978+justrach@users.noreply.github.com>
Date: Tue, 14 Jul 2026 14:34:48 +0800
Subject: [PATCH] fix(agent): don't peek past a completed stream on a half-open
 socket (#56)
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The SSE reader's post-line reader.peekByte() ran BEFORE the terminal-event check,
which then breaks on [DONE]/response.completed. So on the final line the peek's
result was discarded anyway, but its fill could block forever on a half-open
socket (server gone, no FIN) that the idle-stall watchdog doesn't guard — hanging
an already-complete turn. That is part of #56's "reconnect doesn't reconnect".

Move the peek to AFTER the terminal-event break, matching the loop's documented
intent ("stop instead of waiting for the socket to close"). A completed response
now breaks before peeking; the non-terminal path is byte-for-byte unchanged
(peek -> if (!more) break -> toss the buffered '\n').

Safe by inspection: on a terminal line the loop already broke at the isStreamEnd
check, so `more` was never read there — skipping the peek only removes a useless,
hang-prone fill. Verified: zig build test green + the streaming PTY suite
(test-pty-codex-ws/repl/markdown/spinner) green — no regression in the hot read
path.

Scope: this closes the post-completion subcase. The mid-stream half-open subcase
(peekByte blocking on a NON-terminal line) still needs a watchdog-guarded peek
plus a half-open-socket mock harness to verify — left as a follow-up. Fix-B
(retryable stalls via watchdogError, #134) is already done.

Pre-existing zig-fmt debt in this file (unrelated one-liners) left untouched to
avoid churn.

Refs #56

Co-Authored-By: blackfloofie <265516171+blackfloofie@users.noreply.github.com>
---
 src/agent_stream.zig | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/agent_stream.zig b/src/agent_stream.zig
index 43aa81e9..1b832e8e 100644
--- a/src/agent_stream.zig
+++ b/src/agent_stream.zig
@@ -398,9 +398,6 @@ pub fn postStreamWithClient(self: *Agent, client: *std.http.Client, body: []cons
                 },
             }
         }
-        // End of stream leaves the reader empty; otherwise the '\n' is
-        // still buffered (and consumed below, after the line is handled).
-        const more = if (reader.peekByte()) |_| true else |_| false;
         try full.writer.writeAll(line.writer.buffered());
         try full.writer.writeByte('\n');
         got_body = true; // #134: response bytes are in `full`; a later read error is a clean close
@@ -434,6 +431,13 @@ pub fn postStreamWithClient(self: *Agent, client: *std.http.Client, body: []cons
             if (req.connection) |conn| conn.closing = true;
             return error.Interrupted;
         }
+        // "Is there more?" — peek the next byte, then consume the buffered '\n'.
+        // Deliberately AFTER the terminal-event break above (#56): once
+        // [DONE]/response.completed has landed the turn is complete and we break
+        // there, so this peek never runs on a finished response. Peeking then would
+        // fill-block forever on a half-open socket (server gone, no FIN) and hang
+        // the completed turn — the exact wedge the idle-stall watchdog can't see.
+        const more = if (reader.peekByte()) |_| true else |_| false;
         if (!more) break;
         reader.toss(1);
     }