Status — SEP-2549 (TTL for List Results / `ttlMs` + `cacheScope`)

Track: B — independent, starts now.
Spec: seps/2549-TTL-for-list-results.md · merged 2026-05-15

Nothing in main (no ttlMs, no cacheScope, no CacheableResult).
Closed exploration: feat(core,client,server): ttl on list results (SEP-2549) #2070 — added ttl?: number to the four list-result types + McpServerOptions.listTtlSeconds; client marks tool-metadata cache stale after ttl; clamped to ≥1s.
- Note: feat(core,client,server): ttl on list results (SEP-2549) #2070 used ttl (seconds). The spec landed on ttlMs (milliseconds) + a sibling cacheScope field. The PR will need a small reshape.

R-2549-1 (wire): Server MUST include ttlMs (≥0) and cacheScope ("public" | "private") on tools/list, prompts/list, resources/list, resources/templates/list, resources/read results
R-2549-2: Client SHOULD refetch on next access after ttlMs expires (MAY serve stale on refetch error)
R-2549-4: list_changed notifications still delivered if subscribed — ttl is a hint, not a replacement
R-2549-8: Same cacheScope on every page of a paginated list response
R-2549-10 (sdk): Polling helpers MUST apply jitter + backoff (spec text and SEP MD differ on MUST vs SHOULD — caching.mdx wins per spec page)
R-2549-11: Receiving list_changed / resources/updated invalidates the client cache regardless of remaining TTL
R-2549-12: Absent ttlMs on a response → treat as 0 (immediately stale) — BC with pre-2549 servers
R-2549-13: Negative ttlMs → treat as 0
R-2549-14: Cursor invalid (-32602 on next-page fetch) → discard all cached pages, re-fetch from page 1
R-2549-3 (guidance): Per-page ttlMs; freshness lives on ListToolsResult, not on Tool
R-2549-7 (security MUST NOT): Shared caches MUST NOT serve cacheScope: "private" to a different user — keyed on auth principal if the SDK ships a shared-cache helper

Rename and reshape feat(core,client,server): ttl on list results (SEP-2549) #2070's ttl: number → ttlMs: number + add cacheScope: 'public' | 'private' on a shared CacheableResult interface
Server: populate from McpServerOptions.{listTtlMs, defaultCacheScope}
Client cache: TTL-based staleness + list_changed/resources/updated invalidation hooks
Pagination semantics: page-level TTL, cursor-invalid → discard
Polling helper (if shipped): jitter + exponential backoff

Pure result-shape change, no cross-track dependencies. Can land on main ahead of the v2 stack and be rebased.

Status — SEP-2549 (TTL for List Results / ttlMs + cacheScope)