observability-collector: drive trace-store prune on a cadence

Wave 2 (final) of the dedup/storage-growth milestone (notes §12).

- pure shouldPrune(now,lastPruneAt,intervalMs) cadence helper (injected clock).
- main.ts calls store.prune(DEFAULT_RETENTION) on a coarse cadence
  (--prune-interval-ms, default 60s; host-bin-overridable), far less frequent
  than a drain. Prune errors are logged and never stop the tail loop.
- confirmed body inserts flow through trace-store's content-addressed path.
- glossary: content-addressed body, trace retention, prefix fingerprint,
  warm vs real.

typecheck EXIT 0; biome clean; vitest 576; bun 100->106, 0 fail.

1 files changed, 4 insertions, 0 deletions

diff --git a/GLOSSARY.md b/GLOSSARY.md
index 845b45f..39e618f 100644
--- a/GLOSSARY.md
+++ b/GLOSSARY.md
@@ -26,6 +26,10 @@
 | **chunk** | One ordered piece of a message (text, thinking, tool-call/result, etc.), append-only in the log. | block, segment |
 | **seq** | The monotonic, gap-free, per-conversation sequence number stamped on each chunk as it is appended to the log. The sync cursor: a client requests `?sinceSeq=N` to fetch only newer chunks. Storage/sync metadata, never message content. | cursor (when meaning the number), offset, index |
 | **StoredChunk** | The wire envelope `{ seq, role, chunk }`: a persisted chunk plus its sync metadata. Keeps the pure `chunk` free of storage concerns while a flat seq-ordered stream stays both syncable and regroupable into messages. | seq'd chunk |
+| **content-addressed body** | A verbatim trace `body` stored once in the trace store keyed by its content hash (SHA-256); duplicate bodies (cache-warming resends, any repeat) collapse to a single stored row referenced by hash. The trace store's de-duplication mechanism. | (not fingerprint-keyed) |
+| **trace retention** | The trace store's `prune(policy)` pass that bounds storage growth: age-based delete + drop-oldest byte-cap eviction of records/bodies + orphaned-body GC. "Rotation" is one part of retention, not a separate thing. | rotation (as a separate concept) |
+| **prefix fingerprint** | A hash of a provider request's cacheable prefix (up to the `cache_control` breakpoint), stamped as a queryable attribute to flag a prompt-cache bust (the fingerprint changed unexpectedly between a warm and a real send). A cache-bust DEBUGGING signal — NOT the body-dedup key. | — |
+| **warm vs real (request)** | A `provider.request` flagged `warm` (a periodic rewound resend to keep the prompt cache warm, ≠ `wake`) vs `real` (user-driven). | reheat, cache reheating |
 | **runTurn** | The kernel's turn loop: takes provider + messages + tools + dispatch policy, streams, dispatches tools, emits events. | run, agentLoop |
 | **hook** | A typed extension point. **event** = fire-and-forget, N listeners, error-isolated. **filter** = ordered value-in→value-out chain, in-band. | callback (when meaning a hook), listener |
 | **service** | A single-responder request/response capability fetched via a typed handle. NOT a hook. | — |