agy-proxy: stream resume-retry judges 'no output' before flushing the final line — an unterminated partial delta is silently retried as a fresh conversation (PR #679) #683

Finding

PR #679 (fixes #678, head f935ce0e) judges a failed resume's "no output" condition inconsistently between the two modes of bin/agy-proxy.mjs, because the stream close handler checks hasOutput before flushing the final unterminated line, while the non-stream handler parses the whole stdout buffer before its retry gate:

• Stream (bin/agy-proxy.mjs on PR head): child.on('close', (code, signal) => …) runs the resume-retry check first — if (code !== 0 && !hasOutput && allowRetry && targetConvId) at :471 — and only afterwards flushes the tail line (if (lineBuffer.trim()) { processJsonLine(lineBuffer.trim()); } at :479-481) and the new exit-code failure check (:489). A step_update text delta that arrives as the child's final stdout bytes without a trailing newline is still sitting in lineBuffer at the retry decision, so hasOutput is false even though the run produced output.
• Non-stream (same file, PR head): stdoutBuffer is fully parsed into responseText before the if (code !== 0) block (:580), and the retry inside it is gated on !responseText — so the same run shape is correctly treated as "produced output": no retry, HTTP 502.

Consequence in stream mode: a resumed conversation whose run emits a partial delta in an unterminated final line and then exits non-zero is silently retried as a fresh conversation, and the client receives the fresh run's answer with finish_reason: "stop" and the resumed conversation's id — the failure is never reported, the partial output is discarded, and a second agy run executes even though the retry's own precondition ("failed without output", #678's acceptance criteria) does not hold. Whether the failure is reported or silently swapped for a fresh-conversation answer depends only on whether agy newline-terminated its last JSON line. The sibling proxies flush first: bin/muse-proxy.mjs and bin/codex-proxy.mjs both process a non-empty lineBuffer as the first step of their close handlers before judging the run.

Note the success path already relies on the flush at :479-481 to deliver an unterminated final line, so unterminated tails are a shape this file explicitly handles — just not at the retry decision.

Evidence (reproduced on PR #679 head f935ce0e1a5e4a2caf1880ee4f1badeec1638865)

Ran the PR-head bin/agy-proxy.mjs with a stub agy at $HOME/.local/bin/agy (the proxy's own binary resolution; the bin/agy-proxy.test.mjs pattern from the PR), requests carrying x-conversation-id: conv-123:

• Stub, on --conversation: emits {"event":"step_update","step_update":{"text_delta":"partial answer"}} with no trailing newline (non-stream shape: {"response":"partial answer"} likewise unterminated), prints stub agy: run failed midway to stderr, exits 3; a fresh (no-conversation) run succeeds with Hello world:
  • stream → 200, fresh run's Hello world chunk + finish_reason: "stop" + [DONE]; proxy log shows exactly 1 retrying as fresh conversation line — no error event, partial output never sent
  • non-stream → 502 {"error":"agy process exited with non-zero code","code":3,"stderr":"stub agy: run failed midway"} (correct — the control)
• Control, same stub but the partial line is newline-terminated:
  • stream → partial answer chunk, then data:-framed agy execution failed: stub agy: run failed midway error event + [DONE], no stop chunk (the PR's intended new behaviour)
  • non-stream → 502, same as above

So the two modes disagree on identical run shapes, and stream mode disagrees with itself based on a trailing newline. PR #679's new tests cover the resume-retry case only with no output at all (RETRYME) and the partial-output case only without a conversation (FAILPARTIAL, newline-terminated) — the resume + unterminated-partial shape is untested. This is filed against the PR as a follow-up; fixing it inside PR #679 before merge also satisfies this issue.

Dedup: issue searches for agy-proxy return only #678 (OPEN, the exit-code masking this PR fixes — its acceptance requires the retry be preserved for a failed resume with no output, which is exactly the precondition misjudged here) and unrelated port/discovery issues; searches for lineBuffer / unterminated / resume retry return only #678. Cross-repo: bin/agy-proxy.mjs exists only in this repo (no copy in developing-today/opencode, developing-today/openchamber, dezren39/nix — verified by git grep on each clone's origin/main).

Why it matters

The retry exists to recover from a stale conversation id, not to replace a run that already answered in part. Triggering it on a run that produced output hides a real failure (expired auth, CLI crash) behind an unrelated fresh conversation's answer, presented under the resumed conversation's id as a clean stop — the same silent-substitution failure mode #678 was filed for, reachable only in stream mode (the mode OpenCode actually consumes) and only when the final line is unterminated.

Acceptance criteria

• The stream close handler flushes any non-empty lineBuffer (via processJsonLine) before the resume-retry decision, so hasOutput reflects all output the child produced — mirroring the non-stream ordering in the same file and the flush-first ordering in bin/muse-proxy.mjs / bin/codex-proxy.mjs.
• A failed resume (non-zero exit or signal) whose only output is an unterminated final step_update delta is reported as a failure in stream mode — data:-framed error event naming the failure + data: [DONE], no chunk claiming finish_reason: "stop", no fresh-conversation retry — matching the non-stream 502 for the same shape.
• A failed resume with genuinely no output still retries once as a fresh conversation in both modes (the existing RETRYME behaviour), and successful runs with an unterminated final line still deliver that line before the stop chunk.
• A new stub case in bin/agy-proxy.test.mjs pins the resume + unterminated-partial + non-zero-exit shape in stream mode (and the non-stream control); ablating the flush-reorder fails exactly that case, and the agy-proxy + muse-proxy + codex-proxy + proxy-port suites pass.