feat(telemetry): link agent snapshot collection to CC persistence

docs/fleet-cache.md

@@ -17,6 +17,9 @@ and reuse it. The helper checks the key again after building: if inputs changed
 while database reads/grouping were in flight, it discards the result and retries.
 Build errors are returned, not cached; cancelling a reader releases the lock.
 The previous view is not served as a fallback after a rebuild error.
+Retries currently have no fixed limit. Sustained mutations faster than rebuilding
+can delay the rebuilding reader and readers waiting on its lock; bounding this
+behavior is tracked as a reliability follow-up.
 
 Wake uses the same view, but command dispatch still checks the current session;
 a cached route cannot grant access to a disconnected agent.

docs/roadmap.md

@@ -43,7 +43,7 @@ of remembered identifiers based on observation expiry.
 - [x] Separate console, OTLP log, and trace filters using per-layer filtering. Explicit signal config overrides `RUST_LOG`, then CLI verbosity supplies defaults. Unconfigured defaults remain info-level; exporter-failure logs stay local. Live validation pending.
 - [ ] Record hostname-resolution success/failure without exporting hostnames or resolved addresses. Current spans show timing but do not explicitly classify the result.
 - [ ] Investigate the slow resolver with a reproducible device-side check. Timing isolated the phase, not the cause; do not treat instrumentation as a fix.
-- [ ] Propagate trace context for periodic snapshots so agent collection and CC persistence can be inspected together. Commands already have this linkage.
+- [x] Propagate optional W3C trace context for periodic/requested WS snapshots so agent collection and CC persistence can be inspected together. Wire compatibility and context linkage tested; live validation pending.
 - [ ] Add current-state device gauges: stored rows per agent and grouped fleet devices split known/unknown. Define scope and update lifecycle first; never derive gauges from the last filtered UI query.
 - [ ] Decide whether snapshots need persistence acknowledgements. The existing sent-device counter does not prove CC storage; any confirmed-storage metric needs an authoritative measurement point.
 
@@ -52,6 +52,7 @@ or current fleet size. Metric labels should remain bounded; no per-device labels
 
 ## Validation And Reliability
 
+- [ ] Bound fleet-cache rebuild retries under sustained mutations; current stale-build rejection can keep a request waiting while inputs continuously change. Do not silently serve stale wake routes as a fallback.
 - [ ] Reproduce/check Ctrl-C cleanup on the test device: process groups, PTYs, relay tasks, and telemetry shutdown. Leftovers were suspected, not confirmed.
 - [ ] Exercise collector unavailability and recovery with running agent/CC instances. Verify normal operations continue and telemetry queues remain bounded; outage losses are expected under the current best-effort policy.
 - [ ] Validate terminal recovery instrumentation live: generation timing/size, transport attach/resume, and backpressure episodes ending in drain or disconnect.

docs/telemetry.md

@@ -96,7 +96,11 @@ existing debug events too; inspect them before enabling it broadly.
 - `relay_command` on CC propagates W3C context in an optional command field.
   `execute_command` on the agent adopts it; older messages/agents remain compatible.
 - `collect_device_snapshot` and `store_device_snapshot` measure collection and
-  persistence separately. Snapshot traces are not yet linked across the wire.
+  persistence as linked spans across the agent WebSocket. The snapshot carries
+  optional W3C context from collection; CC adopts it after authentication checks.
+  Periodic and requested syncs use the same path. Old messages and empty/invalid
+  context remain valid but do not create a cross-process link. Both processes
+  need tracing enabled and suitable filters/sampling to see both sides.
 - Terminal create/attach/close/resume spans describe lifecycle operations, not
   output chunks. Trace-linked OTLP logs use the SDK's tracing-context bridge.
 - Inventory source spans separate neighbor, DHCP lease, and hook-store reads