Extension Management V2 Implementation Plan

Delivery order

1. Add ExtensionStore, policy migration, global generation, artifact journals, rollback/forward recovery, and V1 projection. Route all ExtensionManager mutations through it and make install activation atomic.
2. Add the daemon operation coordinator, global catalog/mutation routes, workspace projection/activation routes, targeted/all-runtime reconciliation, and the primary-workspace V1 adapter.
3. Add SDK models and polling helpers, watcher generation recovery, CLI/TUI callers, capability negotiation, protocol documentation, and E2E coverage.

extension_management_v2 is advertised only when all three layers are wired.

Required invariants

• state.json is the only commit point and generation never decreases.
• No production caller writes a final extension directory directly.
• Install commits its initial activation policy with the artifact.
• Update preserves identity and activation; uninstall is idempotent at the API.
• Workspace routes mutate policy/runtime only, never artifact ownership.
• Global mutation reconciles all local runtimes; workspace mutation reconciles one target.
• Runtime refresh failure cannot roll back committed global state.
• Preparation concurrency is two across legacy and V2 routes; commit concurrency is one and FIFO by preparation completion order.
• Preparation never mutates final artifacts or runtime, and every successful handle is committed once or disposed.
• Same-artifact stale updates fail with extension_conflict; unrelated artifact and activation commits do not invalidate prepared work.
• Reconciliation occupies neither queue and applied generation never moves backwards.
• V1 routes and capability remain usable by old SDK clients.
• Secrets are redacted from operations, responses, and logs.

Verification gates

Targeted unit tests cover store migration, policy precedence, concurrent store instances, journal recovery, CLI scope behavior, daemon routing/trust/fanout, two-slot preparation, preparation-ready commit ordering, queued abort, same-artifact conflicts, watcher polling, SDK paths, and operation polling. Repository completion gates are package builds, typecheck, lint, integration daemon route tests, and the E2E plan in .qwen/e2e-tests/extension-management-v2.md.

Before completion, audit architecture boundaries, crash/error paths, compatibility, concurrency, redaction, tests, maintainability, and simpler alternatives repeatedly until no new actionable issue is found.