fix(archive): make scenario-drift check multiplicity-aware (#1246)

[vishnujayvel]

Summary

Closes a residual silent-drop path in the #1246 scenario-drift gate.

PR #1252 added findMissingCurrentScenarios so a stale MODIFIED block
cannot overwrite the canonical requirement when it omits scenarios that
already exist. That gate stored incoming scenario names in a Set and
filtered by membership. When the current requirement has N scenarios
sharing one name and the MODIFIED block keeps M < N, every current
instance still "matches," missing is empty, and archive still succeeds —
dropping the extras with no abort.

This change makes the check multiplicity-aware: count occurrences per
scenario name; a current instance is missing when remaining incoming count
for that name is zero. Error message shape is unchanged.

Credits

• Issue reporter: @stanleykao72 —
  sequential-archive scenario drop (Archiving two changes that MODIFY the same requirement silently drops scenarios (distinct from #1112) #1246).
• Root-cause analysis (duplicate-name blind spot + multiplicity sketch):
  @HerbertGao — issue comment on Archiving two changes that MODIFY the same requirement silently drops scenarios (distinct from #1112) #1246.
  Implemented and verified independently against a failing repro on main.

Related

• Partial fix: fix archive scenario drift for #1246 #1252 / 7e21cc5 (fix archive scenario drift for #1246)
• Issue: Archiving two changes that MODIFY the same requirement silently drops scenarios (distinct from #1112) #1246

Changes

• src/core/specs-apply.ts: findMissingCurrentScenarios uses a
  remaining-count Map instead of a name Set.
• test/core/archive.test.ts: regression — current has two
  #### Scenario: Validate blocks; MODIFIED keeps one → archive aborts,
  main spec untouched, change not archived.

Verification

• Pre-fix repro on unmodified main: buildUpdatedSpec succeeded with
  Scenario: Validate count 1 and no malformed body (silent drop).
• pnpm exec vitest run test/core/archive.test.ts — 40/40 passed
• pnpm run lint — 0 errors; 1 pre-existing warning in
  src/core/references.ts (unused eslint-disable; present on
  origin/main)
• pnpm run build — passed
• Revert-proof: restore Set-based findMissingCurrentScenarios, keep new
  test → FAIL (expected 1 to be 2 — silent drop); restore fix → PASS
• pnpm test — 2014 passed; 13 failed in e2e/config/store/artifact
  files. Same 13 failures reproduce on unmodified origin/main
  (NO_COLOR/FORCE_COLOR chalk + stderr noise). Labeled pre-existing;
  not introduced by this change.

Test plan

• CI green on this branch
• Review residual path: duplicate scenario names within one requirement,
  MODIFIED retains fewer copies → abort with
  scenario(s) not present in the modified block: "…"
• Existing distinct-name drift case from fix archive scenario drift for #1246 #1252 still aborts as before

Summary by CodeRabbit

• Bug Fixes

  • Improved spec validation when multiple scenarios share the same name.
  • Archive operations now correctly abort when a modified block omits duplicate scenario occurrences.
  • Prevented partial changes, incorrect archiving, and unintended file updates in these cases.

• Tests

  • Added regression coverage for duplicate-named scenarios during archive operations.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 596d6ba and 972122d.

📒 Files selected for processing (2)

• src/core/specs-apply.ts
• test/core/archive.test.ts

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📝 Walkthrough

Walkthrough

Scenario drift detection now compares scenario multiplicity instead of name presence alone. A regression test verifies that archiving aborts, preserves the main spec, reports the failure, and leaves the change directory unarchived when duplicate scenarios are reduced.

Changes

Scenario multiplicity handling

Layer / File(s)	Summary
Count-based scenario validation src/core/specs-apply.ts, test/core/archive.test.ts	findMissingCurrentScenarios detects surplus duplicate scenarios using occurrence counts, and archive coverage verifies abort and preservation behavior.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• Fission-AI/OpenSpec#1252: Updates the same scenario-drift validation path and related archive regression coverage.

Suggested reviewers: tabishb, clay-good

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: making the archive scenario-drift check multiplicity-aware.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[alfred-openspec]

The counted Map closes the duplicate-name multiplicity blind spot without changing the existing error contract, and the regression covers the important safety guarantees: the main spec stays untouched and the change remains unarchived. The exact head is green across the full CI matrix.