🐛 fix(delegate): strip kanban toolset from delegated children

[cwest]

Why

A worker that spawns a delegate_task subagent can have that subagent inherit the kanban toolset. Because a delegated child also inherits the parent process's HERMES_KANBAN_TASK env, the child's end-of-run kanban_complete (called with no explicit task_id) falls back to that env var and resolves the parent's card — falsely flipping it to done with the child's summary while the real deliverable was never produced (false-done, control-surface-bleed).

What

Add "kanban" to the composite toolsets stripped from every delegated child in _strip_blocked_tools (tools/delegate_tool.py), alongside delegation and code_execution. Children get no card-terminal authority:

• The strip is unconditional. Orchestrator children re-gain delegation by role after the strip, but there is no kanban re-add, so no delegated agent (leaf or orchestrator) ever holds the kanban terminal verbs bound to its parent's card.
• Applies on both toolset-resolution paths — an explicitly requested toolsets=["kanban", ...] and the no-toolsets-requested inheritance of the parent's full set both route through _strip_blocked_tools.

How verified

• Root cause traced end to end: child toolset inheritance at _build_child_agent (parent set → _strip_blocked_tools) + kanban_complete's _default_task_id fallback to HERMES_KANBAN_TASK.
• Behavior-contract tests added in tests/tools/test_delegate_toolset_scope.py: a child never receives kanban on the explicit-request path or the inherited-set path. RED before the fix, GREEN after.
• Targeted suites green: test_delegate_toolset_scope.py, test_delegate.py (except one pre-existing timing-sensitive heartbeat flake that passes 3/3 in isolation), test_kanban_tools.py.
• Full suite: the remaining failures reproduce identically on the pristine base commit (a7ed14f) with this change reverted — they are pre-existing environmental/parallel-load failures, not regressions from this change.

Verified STILL BROKEN on origin/cwest/integration HEAD a7ed14f before the fix.

[cwest]

The root cause holds end to end: a delegated child inherits the parent's HERMES_KANBAN_TASK, and kanban_complete with no explicit task_id falls back to that env var, so a child that kept the kanban toolset would resolve and retire the parent's card. Adding "kanban" to the composite strip set closes that off.

The scoping is right. All four toolset-resolution branches in _build_child_agent route through _strip_blocked_tools (explicit request, parent_enabled inheritance, derived parent set, and the DEFAULT_TOOLSETS fallback), and the orchestrator re-add only restores delegation, never kanban — so no child, leaf or orchestrator, keeps card-terminal authority. The kanban verbs live under exactly one toolset name, and nothing else includes it, so stripping the name is sufficient; there's no alias path that reintroduces them.

The two new tests earn their place: reverting the one-line change turns both red (2 failed, 9 passed), and they assert the contract on both the explicit-request and inherited paths rather than snapshotting a value. Ran the targeted file (11 passed), plus test_delegate.py and test_kanban_tools.py together (252 passed, 0 failed) against the head SHA in a throwaway clone. No changes needed.