fix(agents): clean up orphaned sub-agent sessions on parent reset

[sytone]

Closes #507

Changes

ISubAgentManager (new method)

• CleanupChildSessionsAsync(SessionId parentSessionId, CancellationToken ct) — kills running sub-agents for a parent session and archives their child sessions

DefaultSubAgentManager (new impl)

• Iterates all child sub-agents for the given parent session
• Cancels each running timeout CTS
• Calls CleanupChildAgentAsync to stop the agent and unregister from registry
• Updates sub-agent status to Killed if still running
• Archives each child session in ISessionStore (non-fatal on failure)

GatewayHub.ResetSession (hooked in)

• Optional ISubAgentManager param added to constructor
• Calls CleanupChildSessionsAsync after supervisor stop, before memory flush and session archive
• Non-fatal: reset proceeds even if cleanup throws

NoOpSubAgentManager in SessionsController

• Added CleanupChildSessionsAsync returning 0 (no-op)

Tests (6 new)

• CleanupChildSessionsAsync_ReturnsZero_WhenNoChildrenExist
• CleanupChildSessionsAsync_ArchivesChildSession_WhenChildExists
• CleanupChildSessionsAsync_IsNonFatal_WhenSessionArchiveFails
• CleanupChildSessionsAsync_DoesNotCleanOtherParentSessions
• ResetSession_CallsSubAgentCleanup_WhenManagerProvided
• ResetSession_ProceedsNormally_WhenNoSubAgentManager

1642/1642 gateway tests + full suite passing.

[sytone]

Farnsworth Review — PR #508

CI: ✅ All checks passing (build-and-test, CodeQL, Security Scan)
Merge conflicts: ✅ Clean (MERGEABLE)
Conventional commit title: ✅ fix(agents): clean up orphaned sub-agent sessions on parent reset

Test coverage:

• ✅ CleanupChildSessionsAsync called on ResetSession
• ✅ Non-fatal error path (exception swallowed, reset continues)
• ✅ Happy path with multiple child sessions
• ✅ No-op when no child sessions exist
• 6 new tests; 1642/1642 pass

Spec completeness vs OpenClaw finding: Correctly addresses orphaned sub-agent session cleanup. Optional DI param keeps it backward-compatible. NoOpSubAgentManager updated appropriately.

LGTM. Ready to merge.

[sytone]

Closing as part of a planned hard-reset of the in-flight branch set so the new domain-model refactor can land on a clean trunk.

Audit verdict: close

Rationale: Touches the reset path that Phase 3c rewrites canonically. Will be subsumed.

The new plan (in session state) reshapes core types: Citizen (User+Agent union), Vogen-generated value objects, ThreadId removed in favour of composite ChannelAddress, mark-not-delete compaction, centralised SessionContextProjector, single-path routing. Many in-flight branches touch contracts that are about to change — rebasing later would be more work than rebuilding on the new shape.

If this work is still wanted, refile as a new issue/PR against the post-refactor contracts.