feat(tune): let the agent that identified a cost cluster first work it

Before investigating or implementing a cost cluster (one step, hot path or
repeated call, named by its log line and number), tune now runs the
coordinate skill and asks every other agent session on the machine whether
the cluster is already identified. The earliest claim that carries the
measurement works it; the others hand over their findings and move on, so
no cluster gets two competing optimizations. A claim ends with a result, a
proposal, an abandoned attempt or an operator reassignment.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

skills/tune/SKILL.md

@@ -5,8 +5,9 @@ description: >
   build and gate runtime, hot code paths) without reducing logic, coverage or
   correctness, including a change of language where measurement justifies it.
   Asks once per session what to examine and which limits apply, measures from
-  logs, hardens every candidate with the dialectic skill and funnels each
-  optimization through a sidetree. Trigger on /tune, when a job dies on its time
+  logs, coordinates every cost cluster with the other agents so the one who
+  identified it first works it, hardens every candidate with the dialectic skill
+  and funnels each optimization through a sidetree. Trigger on /tune, when a job dies on its time
   budget, when a pipeline or deploy grows slower, or when the operator asks
   where the time goes. Portable across projects.
 ---
@@ -102,6 +103,27 @@ Discard a before/after pair, not just its noise, when:
 - Pruning build caches to free disk costs a cold rebuild of every custom image
   on the next run. Name that cost before anyone prunes.
 
+## Coordinate every cost cluster
+
+A cost cluster is one place the time goes: one step, one hot path, one
+repeated call, named by its log line and its number. Before investigating or
+implementing a cluster, run the `coordinate` skill for it, and send the
+question to every other agent session on this machine, not only the branch
+lineage: has anyone already identified this cluster?
+
+- **The first to identify a cluster works it.** "First" is the earliest claim
+  that names the cluster's log line and number, by message time. A claim
+  without a measurement does not count.
+- **Someone was earlier:** stop on that cluster. Send them your measurements
+  and findings, then move on to the next cluster. Never build a second
+  optimization of the same cluster.
+- **You are first:** announce the claim with the log line, the number and the
+  sidetree branch, then work it. A silent peer is not a competing claim;
+  proceed after a bounded wait.
+- **A claim ends** when its holder reports the result, a proposal or an
+  abandoned attempt, or when the operator reassigns it. Only then may another
+  agent take the cluster.
+
 ## Levers that usually pay
 
 - **Batch per-item process spawns**: N calls that each boot an interpreter or
@@ -154,7 +176,9 @@ failure, or only moves the cost somewhere the measurement does not look.
 ## The loop
 
 1. Measure, and name the single biggest cost with its log line and number.
-2. Form one candidate for it, after the branch search and the floor check.
+2. Coordinate the cluster with the other agents; work it only when you
+   identified it first, otherwise hand over your findings and take the next.
+   Then form one candidate for it, after the branch search and the floor check.
 3. Harden it with the `dialectic` skill.
 4. Funnel it through a sidetree; merge what reaches the bar, submit the rest as
    proposals. Re-measure from the same source under the same conditions and