fix: lifecycle performance cliffs in change check/list/correct-owner (closes #439)

[0xLeif]

⚠️ Status note

This PR currently contains 1 of 2 changed files. src/change.rs (860KB) could not be uploaded through the automation channel — the complete 31KB patch (w6-439.patch, applies cleanly on main @ ce66973, commit 73ad0d1) is attached to the task report. The branch will not compile until the change.rs portion lands.

Problem

Lifecycle commands degraded superlinearly at modest scale: change check hit double-digit seconds at 20 changes, change list/status cost ~190 ms per change, and change correct-owner batches revalidated every correction after each appended entry (O(entries^2) Git-backed ownership lookups).

Root causes

• Read-only lifecycle surfaces repeated repository-global Git lookups and the full (doubled) Git evidence pipeline for every change, and terminal-evidence validation recursed over accepted chains with a fresh memo per change — thousands of git subprocess spawns at 20–50 changes.
• correct-owner batches re-validated all pre-existing corrections after every appended entry, each with its own canonical-spec evidence collection.

Fix

• Read-only commands (list/status/show/check) now run in a scoped per-command memoization scope: repository-global Git facts, per-candidate-set evidence, project input digest, and terminal-evidence validity are computed once per command. Mutating commands never install the scope; the Git index race guard still re-reads index contents every collection.
• correct-owner validates pre-existing corrections once up front and resolves canonical module ownership at most once per module (fail-fast entry naming and error messages unchanged).
• The bounded Git runner polls on a 200µs quantum instead of 2ms.

Measured (debug builds, 20/50 chained changes, half accepted)

Command	Before	After
change check @20	11.2s (3621 git spawns)	1.4s (599 spawns)
change list @20	13.0s	1.9s
change list @50	30.6s	3.8s
change check @50	16.0s	4.1s
correct-owner 20-entry batch	19.9s	0.25s

Scaling is now near-linear. Regression tests (read_scope_memoizes_repeated_summary_git_lookups, read_scope_reuses_git_evidence_for_repeated_candidates) assert identical summaries with strictly fewer git subprocess spawns (spawn-count hooks, no wall-clock timing). Full cargo test green (except one pre-existing root-only failure) and cargo clippy -- -D warnings green.

Closes #439

[github-actions]

❌ Corvin says...

      _
    <(;\  .oO(oh no...)
     |/(\
      \(\\
      " "\\

"Caw... your imports are all over the place."

CI Summary

Check	Status
Validate action.yml	✅ Passed
Packaged Action Consumer	❌ failure
Dependency Audit	✅ Passed
Code Coverage	❌ failure
Format Check	✅ Passed
Docs Site	✅ Passed
Spec Validation	❌ failure
Tests (build, test, clippy)	❌ failure
VS Code Extension	✅ Passed

---

_{Powered by corvid-pet}