fix(security): make get_products retry-safe

[bokelley]

What changed

• classify polymorphic get_products as state-mutating and require a caller-owned idempotency key across schemas, manifests, MCP/V5/V6 routes, Addie, evaluation tools, docs, examples, and compliance fixtures
• enforce schema-first validation, exact replay/conflict behavior, advisory-success caching, current-context echoing, durable proposal finalization, and per-proposal distributed serialization
• make task-augmented retries recover successful operations before handler re-entry, including cache-publication failures, with recovery receipts retained for the full replay window
• reject mixed finalize/refine requests before cache reservation or mutation and preserve INVALID_REQUEST field mapping through V6
• add compliance scenarios and regression coverage for async task replay, overlapping finalization sets, caller key propagation, task recovery, persistence reload, and V5/V6 parity

Why

get_products is polymorphic: wholesale discovery is read-like, but async execution, refinement, and proposal finalization can create tasks, persist session state, hold inventory, and create insertion orders. Treating the whole task as read-only allowed ambiguous retries to repeat those side effects.

Impact

Callers must now send a valid idempotency_key on every get_products request and reuse it only for exact retries. Existing 3.1 behavior remains documented as a compatibility grace period only for guaranteed side-effect-free synchronous reads.

Validation

• security, JavaScript protocol, and Node.js testing expert reviews: clean
• 664 focused server unit tests
• 3 targeted V6 tenant route tests
• TypeScript no-emit check
• Semgrep: 0 findings
• schema and compliance builds
• 55 simple examples, 139 composed-schema examples, and storyboard lint suites
• changeset protocol-scope check and Changesets status
• git diff --check

Root package.json, package-lock.json, and immutable versioned dist artifacts are intentionally unchanged.