Merge branch 'worktree-agent-a63474e92b05425a5'

# Conflicts:
#	Cargo.lock
#	Cargo.toml

tickets/004-metrics-api.md

@@ -0,0 +1,31 @@
+# 004 — Metrics API
+
+## Summary
+
+Expose param/metric declarations and bucket data over HTTP so the frontend (and the
+filter/dashboard query engines) can declare metrics and read their values.
+
+## Scope
+
+- `POST /api/params` — declare a param ([001](001-param-declarations.md)).
+- `POST /api/metrics` — declare a metric ([002](002-metric-declarations.md)).
+- `GET /api/metrics` — list declared metrics (+ their declared params/labels).
+- `GET /api/metrics/:name` — query bucket values for a metric, filtered by label
+  selector and time/sequence range, mirroring the existing `LogsParams`/
+  `TimelineParams` pattern in `dto.rs`.
+- Follow the existing engine architecture: new `EngineQuery`/`EngineMessage` variants,
+  handled in `engine.rs`'s single-owner loop, DTOs added to `dto.rs`, routes added to
+  `api.rs`'s router — no new locking or shared state.
+
+## Acceptance criteria
+
+- Declaring a param/metric via the API round-trips through to engine state and shows
+  up in `GET /api/metrics`.
+- Querying a metric's bucket values supports the same start/end and limit-style
+  params as the existing logs/timeline endpoints.
+- Bad declarations (invalid regex etc.) return a 4xx with a useful error body, not a
+  500 or silent no-op.
+
+## Depends on
+
+- [003 — Metric bucket derivation](003-metric-bucket-derivation.md)