feat(specialist): add immediate specialist handoff

[wen2zhou]

Problem

• Switching specialists mid-turn only hands off the current turn at the next turn boundary, so the new specialist loses the in-flight context.
• Specialist switch/delete approval cards show raw redacted JSON, which is hard for users to read and reason about.
• Specialist updates (including renames) travel a privileged approval path, and a renamed specialist keeps its old display name in the Settings list.

Proposed change

• Immediate handoff: switching specialists hands the in-flight turn to the switched specialist right away. The switch approval is bound to the exact outer repl_execute completion via a per-control invocation identity, so an approved continuation can re-enter the control queue safely without deadlock.
• Approval cards: switch cards now show the resolved specialist identity, capability scope, and current → target direction instead of redacted JSON (with a stale-warning fallback when the target was renamed/removed/disabled mid-request); delete cards get a friendly detail block with a destructive primary action and a fail-closed binding warning. A new deeplink opens the specialist's Settings editor from the card.
• Approval rework: specialist updates (including renames) are now ordinary chat-reviewed mutations; only delete and switch keep approval cards. The revision guard and atomic single-profile commit are preserved, and renames sync displayName into the Settings specialist list.
• Scope: handoff skills are scoped to the switched specialist; empty handoff snapshots are stabilized.
• Build: exclude .codex agent worktrees from vitest discovery and ESLint scanning (same duplicate-source rationale as .claude/.worktree).

Scope and non-goals

• Provider-specific cancel/reconfigure/continuation behavior is out of scope: this change owns the provider-neutral completion boundary (NotebookControlCompletionInterceptor), while concrete framework adapters (Codex, OpenCode) build on it.
• No database schema changes.

Acceptance criteria and validation

Behavior	Project-owned check	Result
Immediate handoff lifecycle (pending intent → completion capture → continuation)	src/main/agents/handoff-lifecycle*.test.ts, src/main/agents/completion-handoff*.test.ts, src/main/agents/handoff-lifecycle.integration.test.ts	passed
Control completion binding & re-entry	src/main/acp/codex-completion-handoff.integration.test.ts, src/main/agents/completion-gate.execute-control.integration.test.ts	passed
Switch approval card details & stale fallback	src/renderer/src/pages/workspace/PermissionApprovalControls.specialist-switch.render.test.tsx	passed
Delete card & fail-closed warning	src/renderer/src/pages/workspace/PermissionApprovalControls.specialist-delete.render.test.tsx	passed
Rename sync & update-as-ordinary-mutation	src/renderer/src/stores/settings-store.test.ts, src/main/agents/agents-mutations.test.ts	passed
Empty handoff snapshot stabilization	src/renderer/src/pages/workspace/WorkspaceMessageScroller.render.test.tsx	passed
Session-aggregate merge (runtime-service + NotebookSession* types)	src/main/notebook/runtime-service.export.test.ts, session lifecycle tests	passed

All listed checks ran after the last material edit (conflict resolution + prettier formatting + eslint ignore config).

• npm run typecheck — passed
• npm run lint — passed (0 errors; 22 pre-existing prettier warnings in untouched files)
• npm test (full suite) — 667 files / 9707 tests passed, 0 failed

Review focus

• Conflict resolution with the upstream session-aggregate refactor (refactor(notebook): extract session aggregate landed on main after this branch was cut): controlInvocationId and beginControlInvocation were migrated onto the NotebookSessionExecutionRequest / NotebookSessionMcpRpcConnection types in session-aggregate.ts, and executeControl now uses session.enqueueControl while keeping the interceptor semantics. Verify the two merge points in src/main/notebook/runtime-service.ts (executeControl and the session.execute call in executeControlExclusive).
• The interceptor may start an approved continuation that re-enters executeControl; the control-queue tail must settle before the handoff completes.