Debug collection commit for the brokerd admin-test hang investigation (M3a
task 19). Contains:
- crates/brokerd/src/broker.rs: hold_open helper (HOLD_OPEN = 2s read-timeout
loop) applied after forbid and after the final send in broker::handle
- crates/brokerd/src/admin.rs: hold_open applied after forbid and after the
final send in admin::handle
- crates/brokerd/src/grants.rs: check_tool_constraints refactor (match guard
instead of nested if)
- docs/M3a/DEBUG-HANDOFF.md: investigation results added (310 runs, zero
hangs reproduced; stalled fsync cannot be fixed without dropping durability)
The implementer log row was committed separately (a6d81d9).
Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)
kyle
d21baa2954