Found via deep workspace inspection during a maintenance cycle: Security
Auditor's hourly cron correctly tries to delegate_task its audit_summary
to PM, the platform proxy rejects with "access denied: workspaces cannot
communicate per hierarchy", the agent falls back to delegating to its
direct parent (Dev Lead), and PM's category_routing dispatcher (#75) is
never reached.
This breaks the audit-routing contract end-to-end. Every audit cycle was
landing on Dev Lead instead of being fanned out via PM's category_routing
to the right dev role (security → BE+DevOps, ui/ux → FE, etc).
## Root cause
`registry.CanCommunicate()` only allowed:
- self → self
- siblings (same parent)
- root-level siblings
- direct parent → child
- direct child → parent
A grandchild → grandparent (Security Auditor → PM, where parent is Dev
Lead and grandparent is PM) was DENIED. The original design wanted strict
hierarchy to prevent rogue horizontal A2A — but it also broke the
fundamental "child can talk to its leadership chain" pattern that any
audit/escalation flow needs.
## Fix
Generalise to ancestor ↔ descendant. Any workspace can talk to any
ancestor (any depth) and any descendant (any depth). Direct parent/child
remains a fast path that avoids the walk. Sibling rules unchanged.
Cousins still cannot directly communicate (would need to go through their
shared ancestor). Cross-subtree A2A is still rejected.
Implementation: `isAncestorOf(ancestorID, childID)` walks the parent
chain in Go with a maxAncestorWalk=32 safety cap so a malformed cycle in
the workspaces table cannot loop forever. One DB lookup per step. For a
typical 3-deep tree, this adds 1-2 extra lookups vs the old direct-parent
fast path. Could be optimized to a single recursive CTE if profiling
shows it matters; not now.
## Tests
- TestCanCommunicate_Denied_Grandchild → REPLACED with two new tests:
- TestCanCommunicate_Allowed_GrandparentToGrandchild
- TestCanCommunicate_Allowed_GrandchildToGrandparent (the actual bug)
- TestCanCommunicate_Allowed_DeepAncestor — 4-level chain
- TestCanCommunicate_Denied_UnrelatedAncestors — ensures cross-subtree
walks still terminate denied
- TestCanCommunicate_Denied_DifferentParents — extended with the walk
lookup mocks so sqlmock doesn't log warnings
- TestCanCommunicate_Denied_CousinToRoot — same
All 13 tests pass clean. The previous direct parent/child / siblings /
self tests are unchanged (fast paths preserved).
## Why platform-level
Per the "platform-wide fixes are mine to ship" rule. Every org template
hits the same broken audit-routing chain — fixing it at the platform
benefits all users, not just molecule-dev. This unblocks #50 (PM
dispatcher prompt) and #75 (category_routing).
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