[interceptors] Data spillover for large tool results #67

Summary

A tool that returns a very large payload consumes the model's context. Add an interceptor that stores large results out of band and returns a preview plus a resource URI.

Reference

• ts:core/interceptors/data-spillover.interceptor.ts: DataSpilloverInterceptor. URI prefix defaults to resource://data-spillover/. A payload over the store's maxBytes raises PayloadTooLargeError.
• ts:core/interceptors/spillover/: spillover-store.interface.ts, memory-spillover.store.ts (TTL + LRU), fs-spillover.store.ts, preview-generator.ts, types.ts.

Scope

• A SpilloverStore protocol (put, get, delete, TTL), with MemorySpilloverStore and FileSpilloverStore.
• DataSpilloverInterceptor(threshold_bytes=..., store=..., resource_uri_prefix="resource://data-spillover/"), usable with @use_interceptors(...).
• A preview generator for lists, dicts and strings: head items, counts, truncated text.
• Spilled payloads are served as MCP resources, scoped to the caller.
• File store: paths cannot escape the store root, total size is capped, and expired files are cleaned up.

Acceptance criteria

• Results under the threshold are returned unchanged.
• Results over the threshold return a preview, a URI and the original size; reading the URI returns the full payload.
• An expired payload returns not-found.
• A different principal cannot read the URI.
• A path-traversal attempt on the file store fails.