[Issacboy123]

Summary

Spawn provenance searched all persisted entries, so reused tool-call identifiers could bind a child to an older or abandoned assistant turn. This PR resolves the origin from the newest matching spawn_agent call on the currently selected branch while retaining fail-closed behavior when no match exists.

Reasoning

The selected branch is the authoritative history for the active model call. Traversing it newest first handles identifier reuse without changing stored sessions or requiring globally unique IDs, and matching the tool name as well as the identifier prevents collisions with other tools. Keeping the no-match rejection avoids inventing provenance when current history cannot support it.

Changes

• Replaced global persisted-entry matching with newest-first selected-branch traversal.
• Required both the executing tool-call identifier and the spawn_agent tool name to match.
• Preserved existing origin fields for matched calls and the invariant rejection for unmatched active spawns.
• Added regressions for reused identifiers, same-ID calls to other tools, abandoned branches, and no-match rejection.
• Recorded the provenance fix in the changelog.

Testing

• node ../../node_modules/vitest/dist/cli.js --run test/suite/subagent-registration.test.ts
• node ../../node_modules/vitest/dist/cli.js --run test/suite/agent-session-prompt.test.ts test/suite/subagent-services.test.ts test/suite/subagent-registration.test.ts test/suite/subagent-coordination.test.ts test/suite/subagent-parent-messaging.test.ts test/subagent-controller.test.ts
• node ../../node_modules/vitest/dist/cli.js --run test/session-manager/tree-traversal.test.ts
• npm run check