perf: coalesce compose inspector refresh work

[baron]

Summary

• skip redundant compose-inspector resolver work when token metrics complete with an identical already-published snapshot
• stop the presenter wrapper from observing all runtime snapshot changes when only the drawer and token pill need that observation
• prevent the token estimate pill from scheduling refresh work during SwiftUI body evaluation
• extend coordinator coverage to prove identical completed snapshots do not trigger another resolve

Follow-up to #535 after a performance-focused audit.

Review notes

The audit also identified larger possible costs in full-content rereads for selected worktree files and periodic Git selection reconciliation. Those are intentionally deferred until measured; this PR keeps the change small and addresses only confirmed redundant invalidation/work.

A Fable 5 High design review caught an unsafe first attempt to coalesce in-flight refreshes: a failed or cancelled request could consume the only completion event. That optimization was removed, preserving retry semantics while retaining safe completed-snapshot coalescing.

Validation

• make dev-test FILTER=AgentSelectedFilesModelCoordinatorTests — 29 tests, 0 failures
• make dev-format — clean
• make dev-lint — clean
• contribution commit and push preflights — passed

The PR-ready full root suite completed with four failures in unrelated concurrency/timing tests:

• CodemapBindingEngineInvalidationTests.testRequestReservationAndCancellationDuringValidatedReadReleaseExactlyOnce
• DurableArtifactIdentityLeaseGCTests.testQuarantineGraceAbandonedWorkCleanupAndDirectOldVersionDeletion
• WorkspaceCodemapBindingEngineObservabilityTests.testGraphIndexManifestPersistenceOccursOnceAtEnumerationSeal
• WorkspaceFileContextStoreTests.testAggressiveAppliedIngressLimitsConcurrentRootFlushFanOut

The changed coordinator suite remained green. A focused rerun was queued but cancelled before acquiring the machine-wide heavy slot because another worktree held it; hosted exact-head CI should provide the final broad signal.