yoi/docs/report/spawn-worker-delegation-scope-mismatch-20260730.md

SpawnWorker rejects a workspace subdirectory inside the parent write boundary

Date: 2026-07-30

Symptom

While implementing the multiplexer protocol foundation, the parent Worker could write the checkout but could not delegate crates/protocol to a spawned Coder:

Invalid argument: requested child scope .../checkout/crates/protocol Write is outside this Worker's delegation scope grant

The requested child scope was a recursive subdirectory of the checkout advertised as writable in the parent instructions. No child was created.

Impact

The parent had to implement and review the protocol slice serially. This removed useful parallel review and made the long Runtime/Server protocol change more interruption-prone.

Suggested improvement

• Make the effective delegation grant visible separately from the Worker's direct filesystem write scope.
• Validate and explain which ancestor rule prevents delegation.
• When a requested child scope is a strict subset of a writable/delegable checkout, accept it consistently.
• Distinguish “parent may write but may not delegate” from a malformed/out-of-bound scope error.