Harden error handling, dependencies, and MCP boundaries

[mikim]

Summary

• Keep explicit phase: "error" events actionable even when normalized error details are absent, including recent-window burst detection.
• Patch vulnerable transitive lockfile entries (fast-uri 3.1.4 and @hono/node-server 2.0.12) without changing parent SDK versions.
• Add opt-in sanitizer input/output budgets for messages, blocks, and UTF-16 text, with deterministic traversal, hook reapplication, bounded impact accounting, and merge amplification protection.
• Replace MCP handler casts with fail-fast Ajv 2020 validation against strict tool schemas and the canonical runtime-event v2 schema.
• Add secure MCP defaults (256 messages / 2,048 blocks / 1,000,000 text code units), a 1,024-character merge-separator ceiling, and real Client + InMemoryTransport integration coverage.
• Include the MCP example build/tests in the root and CI command path.

Why

This closes three reliability gaps found during repository triage: silent no-op recovery for underspecified error events, known vulnerable transitive dependencies, and unvalidated/unbounded MCP tool inputs.

Affected packages

• @ark/sanitize
• @ark/classify
• tooling / docs / MCP example

Validation

• pnpm install --frozen-lockfile
• pnpm check (97/97 tests; typecheck, lint, schema validation, package/MCP builds)
• MCP integration tests (5/5)
• pnpm audit --prod --json (0 vulnerabilities)
• pnpm audit --json (0 vulnerabilities)
• Changesets added for both public package changes
• Independent adversarial review completed with no remaining P1/P2 blockers

Residual boundary

The sanitizer budgets gate known content/messages before transforms and cap normalized output, but they are not a raw JSON-RPC byte limit and do not recursively budget opaque provider-specific fields. That transport/deep-object boundary remains explicitly documented.