Session aggregation follow-ups (RFC-0024): partial-match merging and debug CLI

[eric8810]

RFC-0024 (session aggregation) landed P1–P5. Two smaller items were deferred at the MVP boundary and nothing tracks them:

1. Partial-match merging. The current aggregation only recognizes a "strong prefix" — the new prompt must fully contain a recent call's complete prompt. Partial/prefix-loose matching was deferred; decide whether it is worth the false-positive risk before implementing.
2. Debug CLI. The query surface is library API only; a standalone debugging CLI was deferred ("库 API 为主,CLI 后续"). Note aimux-cli (RFC-0025) now exists and is the natural home for it.