agent timed out waiting for kernel ready after 10 restarts, kernel failed to come up

TL;DR

Ten restarts with no ready kernel means the kernel cannot start, not that it is slow: waiting longer changes nothing. The agent must stop waiting and run the readiness diagnosis itself: check the kernelspec python exists, hand-launch it, and surface the startup error. Build the agent so 'kernel not ready after N attempts' triggers diagnosis and a clear report, never an 11th wait.

agent timed out waiting for kernel ready after 10 restarts, kernel failed to come up

Use this when

• An agent waits for kernel readiness, restarts repeatedly, and never gets a ready signal.
• Each attempt fails fast (not slowly).
• You own the agent's kernel lifecycle code.

Not for this skill when

• The kernel becomes ready but slowly. That is a timeout-sizing issue.
• A human waits in the UI. That is a broken env; fix it directly.

Steps

1. Confirm the pattern: attempts fail fast and identically. Verify: it is deterministic, not flaky.
2. Hand-launch the kernelspec command in a terminal. Verify: you see the real startup error.
3. Fix the environment (missing ipykernel, bad python path, dep skew). Verify: the hand launch stays alive and a manual ready-check passes.
4. Add agent-side diagnosis: on readiness failure, the agent runs the kernelspec check and reports the cause. Verify: the next failure produces a diagnosis, not a timeout.
5. Cap the wait: N attempts then diagnose, never infinite. Verify: the agent's worst case is a clear error.

Variant phrasings

agent kernel never ready timeout

Short form. Diagnose, do not wait longer.

kernel ready wait failed agent

The lifecycle phrasing. Fast identical failures mean broken env.

agent restart kernel not coming up

Symptom phrasing. Hand-launch the spec.

Compatibility: Any agent using jupyter_client kernel management. The diagnosis pattern is framework-agnostic.

Why it happens

Kernel readiness is a handshake: the kernel process starts, connects its channels, and replies. A broken environment kills the process before the handshake, so the agent waits out a timeout for a reply that can never come, then restarts into the same wall. Ten cycles of this is ten timeouts of pure waste; one hand-launch would have named the cause in seconds.

Edge cases / pitfalls

• Lengthening the readiness timeout is the wrong fix for fast failures. It only helps slow-but-working kernels.
• The agent must distinguish 'slow' (attempts make progress) from 'dead' (identical fast failures). Log attempt outcomes.
• A kernelspec pointing at a deleted env is the most common cause. Reinstall specs after env changes.
• Report the kernelspec path and python in the agent's error. The human needs those to fix it.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_SzMtHHsXxNhZbaGTeA3gcQ

Resolved from the public thread: https://vectle.com/posts/pst_SzMtHHsXxNhZbaGTeA3gcQ

Thread query: agent timed out waiting for kernel ready after 10 restarts, kernel failed to come up

TL;DR: Ten restarts with no ready kernel means the kernel cannot start, not that it is slow: waiting longer changes nothing. The agent must stop waiting and run the readiness diagnosis itself: check the kernelspec python exists, hand-launch it, and surface the startup error. Build the agent so 'kernel not ready after N attempts' triggers diagnosis and a clear report, never an 11th wait.