Bug: Subagents silently time out (600000ms) after long parent sessions — spawn never completes

Reporter

Discord user: TiltStable
Discord thread: https://discord.com/channels/1346756824233148527/1529813063631376404

---

Symptom

Subagents (Agent tool with subagent_type) silently time out at 600000ms (10 min) after the parent session runs for a while. No error message — ZCode just returns "Subagent was inactive for 600000ms". The per-subagent exec directory (~/.zcode/cli/exec/sess_subagent_<uuid>/) stays empty (0 bytes) — ZCode never writes the subagent stdout/stderr logs, suggesting the spawn itself does not complete.

---

Repro Steps (reproduced 3× today)

1. Start a long interactive session (~940 log lines / ~688 KB transcript, ~18 prior agent calls).
2. Dispatch any subagent (fable-judge, code-reviewer — same behavior) with any prompt (even a focused 5-question verify prompt with all files prepared locally, NO WebFetch required).
3. Result: "Subagent was inactive for 600000ms".

---

Worked Earlier in the Same ZCode Version

Same subagent (fable-judge) completed successfully earlier this week on a similar task: 335s, 49 tool uses, 718k tokens. Same ZCode version 3.4.2.3624 (installed 2026-07-21, app.asar modified 2026-07-21).

• The same subagent (code-reviewer) ran today with a tightly-scoped prompt and completed in 57s.
• With a broader prompt it hung at 600000ms.

---

What Was Ruled Out

• WebFetch / network: Removed all WebFetch from the prompt, prepared all files locally with curl → Bash → local paths. Still hangs.
• Process leak: Only 6 node.exe running, all are MCP servers (playwright, z_ai, context7 + npx wrappers), ~34 MB each, stable.
• Memory: No OOM, plenty of free RAM.
• File / network speed: curl on the same 87 KB file returns in 0.3s.

---

Hypothesis (low confidence)

Parent session context length / accumulated state affects subagent spawn. Correlation: longer parent session → higher hang rate. But this worked on similarly long sessions a few days ago, so something may have changed.

---

Environment

Detail	Value
ZCode version	3.4.2.3624 (running; app.asar modified 2026-07-21)
MCP servers	4 configured (playwright, z_ai/mcp-server, context7, serena via uvx)

---

Regards,
Roman
http://www.rommark.dev

VIbe Coders Telegram Channel: https://t.me/VibeCodePrompterSystem

Reproduce the hang using a long parent session and the Agent tool, then inspect the per-subagent directory at ~/.zcode/cli/exec/sess_subagent_/ and the reported 600000ms timeout behavior. Compare a focused prompt that completes with a broader prompt that stalls; done means failed spawns return a useful error or complete normally with stdout/stderr logs.