Merge branch 'worktree-agent-a63474e92b05425a5'

# Conflicts:
#	Cargo.lock
#	Cargo.toml

tickets/002-metric-declarations.md

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+# 002 — Metric declarations
+
+## Summary
+
+Implement the `MetricDeclaration` slice of the index: a language/API for declaring a
+metric — a regex that matches a log message plus params extracted from it — so that
+matching logs can later be bucketed ([003](003-metric-bucket-derivation.md)).
+
+## Scope
+
+- `IndexKey::MetricDeclaration { name }` paired with `DataValue::MetricDeclaration`
+  (already sketched in `data_value.rs`: `message_match_regex` +
+  `Vec<RegexToMetricPrimitiveMatcher>`).
+- Engine message(s) to add/list/remove a metric declaration.
+- A metric declaration's params may reference params already declared via
+  [001](001-param-declarations.md) (e.g. label a bucket by an existing param) in
+  addition to inline capture groups on the metric's own regex — decide and document
+  which is supported for v1 (README implies inline capture-group derivation is the
+  primary mechanism: "buckets and parameters can be derived" from the metric
+  declaration itself).
+- Validate the regex and capture-group → primitive-kind mapping at declaration time,
+  same as param declarations.
+
+## Acceptance criteria
+
+- Declaring a metric with a valid regex + param matchers succeeds and is retrievable.
+- Invalid regex, or a matcher referencing a capture group the regex doesn't have, is
+  rejected at declaration time.
+- Declarations sit in their own contiguous range of the BTreeMap
+  (`MetricDeclaration` between `ParamMetricSplit` and `MetricBucketSplit`).
+
+## Depends on
+
+- [001 — Param declarations](001-param-declarations.md) (shares matcher/primitive
+  validation code and the "derive a value from a regex capture" concept).