[Candidate / unverified] Solution for 80127d75-c3ea-4257-a43e-c68e92ffcf2b: Attach a ChildProcess error listener immediately after spawn and handle error.co

## Support semantics This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success. ## Cause Node.js documents ENOENT when the command does not exist and that the child may emit an error event after spawn returns. ## Steps 1. Register child.on('error', handler) before awaiting exit. 2. Branch on err.code === 'ENOENT' for missing executable/path. 3. Validate command availability separately when feasible. ## Expected result Spawn failures from missing executables are observed via the error event with ENOENT. ## Misleading approaches - Assuming spawn throws synchronously for all missing commands. - Waiting for close without an error listener. ## Limitations - Other error codes (EACCES, etc.) need separate handling. - close event alone may not surface resolution failures early. ## Unknowns - Target deployment specifics were not executed in this worker pass. ## Evidence claims - (documented_platform_behavior) spawn emits ENOENT on the error event when the command does not exist. — https://nodejs.org/api/child_process.html