Make mutation checks faster and stricter

[stefan-burke]

Why

Mutation testing should spend time on changes that could compile and ship. The equivalent-mutant list must also stay accurate, and every direct test for changed source should take part in the mutation gate.

What changed

• run each mutation through the pinned Biome and TypeScript checks before starting its tests
• add mutation:audit-equivalents to reject stale, malformed, or statically invalid equivalent entries
• run every direct test mapped to each changed source file
• strengthen the affected tests until every detectable mutation is caught
• share one Biome command between normal linting and mutation tooling

Validation

• mise exec -- deno task precommit
• mise exec -- deno task mutation:audit-equivalents: 428 entries checked, with no stale or statically invalid entries
• mise exec -- deno task precommit:mutation: 753 mutations evaluated, 722 detectable mutations killed, 31 equivalents suppressed, and no survivors or timeouts
• GitHub Test, Merge Check, and deploy/chobble/tickets-turso checks passed
• CodeRabbit reviewed the PR and approved it after three review comments were addressed in commit b3b2e690 (exact CSV rows for servicing policy, curried #fp composition in attendee-edit and Square assertions, shared debugMessages test helper)

Remaining limitation

The deploy/chobble/tickets (Deno Deploy) status failed for commit b3b2e690, but the build logs require console access. The Test workflow and the Turso deploy both passed, and the failure was not reproducible locally — a re-run of the Deno Deploy workflow is the next thing to check on a real machine.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 206e08e0-d41f-4eb7-a4d5-8bfafd3ddcd4

📥 Commits

Reviewing files that changed from the base of the PR and between c3208eb and b3b2e69.

📒 Files selected for processing (6)

• test/features/admin/attendees-edit.test.ts
• test/features/admin/calendar-csv.test.ts
• test/shared/payment-helpers/dispatch.test.ts
• test/shared/square/client.test.ts
• test/shared/square/payment-link.test.ts
• test/test-utils/debug-log.ts

---

📝 Walkthrough

Walkthrough

This PR updates mutation-testing tooling and documentation, adds nullish type guards, refactors attendee payment lookup, revises payment-reference behavior, and expands exact-output and edge-case coverage across CSV, forms, Square, and UI tests.

Changes

Mutation Gate Tooling

Layer / File(s)	Summary
Documentation and configuration AGENTS.md, TODO.md, docs/importer-plan.md, biome.json, deno.json	Documents mutation-gate behavior, configures null-comparison linting, and adds the equivalent-mutant audit task.
Biome command resolution scripts/biome-command.ts, scripts/biome.ts, scripts/mutation/execution.ts, test/scripts/biome-command.test.ts, test/scripts/mutation-execution.test.ts	Adds native Biome detection with pinned npm fallback and wires the resolved command into static lint gates.
Equivalent-mutant auditing scripts/audit-equivalent-mutants.ts, scripts/mutation/equivalent-audit.ts, scripts/mutation/ignore.ts, test/scripts/mutation-equivalent-audit.test.ts	Adds catalog validation, mutant auditing, optional pruning, signal handling, and comprehensive tests.
Mutation catalog and test selection scripts/mutation/equivalent-mutants.txt, scripts/mutation/test-map.ts, scripts/precommit-mutation.ts, scripts/precommit/mutation-step.ts, test/scripts/mutation-test-map.test.ts, test/scripts/mutation-step.test.ts	Revises equivalent-mutant entries and selects all direct tests plus changed integration tests.

Nullish Helper Adoption

Layer / File(s)	Summary
Type guards and production usage src/fp.ts, src/features/admin/*, src/shared/*	Adds isNullish/isNotNullish and replaces direct nullish comparisons across shared and admin code.
Test utilities test/shared/rest/crud-api.test.ts, test/test-utils/*, test/fp/collections.test.ts	Applies and tests the new predicates in test support code.

Domain and Test Coverage

Layer / File(s)	Summary
Attendee payment behavior src/features/admin/attendees-edit.ts, src/shared/db/payment-references.ts, related tests	Uses a single-row booking lookup and verifies refund activity attribution and ordered session IDs.
CSV and form rendering test/features/admin/calendar-csv.test.ts, test/ui/templates/admin/calendar.test.ts, test/shared/forms/rendering.test.ts	Replaces partial assertions with exact CSV and HTML output checks.
Square and UI coverage test/shared/square/*, src/ui/client/*, test/ui/client/admin/*, related tests	Adds request, transport, webhook, logging, loader, DOM-typing, and integration-test coverage.

Estimated code review effort: 4 (Complex) | ~60 minutes

Possibly related PRs

• chobbledotcom/tickets#1717: Both update equivalent-mutant catalog entries.
• chobbledotcom/tickets#1854: Both modify direct-versus-integration mutation test selection.
• chobbledotcom/tickets#1790: Both modify the attendee refresh-payment lookup path.

🚥 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 accurately summarizes the main intent: faster and stricter mutation checks.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch improve-mutation-static-gates

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch improve-mutation-static-gates

---

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@test/features/admin/attendees-edit.test.ts`:
- Around line 180-184: Update the assertion around getAttendeeActivityLog to
replace the native filter/map chain with the repository’s curried collection
utilities from `#fp`, composed functionally. Preserve the existing predicates,
attendee_id/listing_id projection, and expected result.

In `@test/features/admin/calendar-csv.test.ts`:
- Around line 272-320: Strengthen both tests in the “servicing policy” describe
block by replacing broad toContain/not.toContain checks with exact CSV line
assertions using split("\n") and toEqual. Assert the complete header and row
contents, including column order, the service-event label, omitted servicing
ticket URL, retained attendee URL, and logistics columns; use the actual default
values produced by calAttendee/testAttendee.

In `@test/shared/square/client.test.ts`:
- Line 42: Replace each native Array.prototype.map in the debug-log assertions
with the repository’s curried `#fp` mapping utility, composing it with the
call-argument extraction. Apply this in test/shared/square/client.test.ts:42-42,
test/shared/square/payment-link.test.ts:102-105 for the final two calls, and
test/shared/square/payment-link.test.ts:184-187 for the final three calls;
preserve the existing expected values and assertion behavior.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 930f3e79-2734-4925-a27e-a05e222465ad

📥 Commits

Reviewing files that changed from the base of the PR and between e6d32a7 and c3208eb.

⛔ Files ignored due to path filters (1)

• deno.lock is excluded by !**/*.lock

📒 Files selected for processing (55)

• AGENTS.md
• TODO.md
• biome.json
• deno.json
• docs/importer-plan.md
• scripts/audit-equivalent-mutants.ts
• scripts/biome-command.ts
• scripts/biome.ts
• scripts/mutation/equivalent-audit.ts
• scripts/mutation/equivalent-mutants.txt
• scripts/mutation/execution.ts
• scripts/mutation/ignore.ts
• scripts/mutation/test-map.ts
• scripts/precommit-mutation.ts
• scripts/precommit/mutation-step.ts
• src/features/admin/api-groups.ts
• src/features/admin/api-holidays.ts
• src/features/admin/attendees-edit.ts
• src/features/admin/calendar-csv.ts
• src/fp.ts
• src/shared/db/activityLog.ts
• src/shared/db/payment-references.ts
• src/shared/forms/rendering.tsx
• src/shared/required-value.ts
• src/shared/rest/crud-api.ts
• src/shared/runtime.ts
• src/shared/square.ts
• src/ui/client/admin/bundle-loader.ts
• src/ui/client/dom.ts
• test/features/admin/attendees-edit.test.ts
• test/features/admin/calendar-csv.test.ts
• test/fp/collections.test.ts
• test/lib/test-utils/error-paths.test.ts
• test/scripts/biome-command.test.ts
• test/scripts/mutation-equivalent-audit.test.ts
• test/scripts/mutation-execution.test.ts
• test/scripts/mutation-step.test.ts
• test/scripts/mutation-test-map.test.ts
• test/shared/db/activityLog.test.ts
• test/shared/db/payment-references.test.ts
• test/shared/forms/rendering.test.ts
• test/shared/merge/attendee-merge/checkout-stage-cleanup.test.ts
• test/shared/rest/crud-api.test.ts
• test/shared/square/client.test.ts
• test/shared/square/payment-link.test.ts
• test/shared/square/request-init.test.ts
• test/shared/square/rest-transport.test.ts
• test/shared/square/retrieve-refund.test.ts
• test/shared/square/webhook.test.ts
• test/test-utils/db-helpers/listing-forms.ts
• test/test-utils/form-values.ts
• test/ui/client/admin/bundle-loader.test.ts
• test/ui/client/admin/logistics-map-loader.test.ts
• test/ui/client/admin/markdown-editor-loader.test.ts
• test/ui/templates/admin/calendar.test.ts

💤 Files with no reviewable changes (4)

• test/lib/test-utils/error-paths.test.ts
• test/ui/client/admin/markdown-editor-loader.test.ts
• test/ui/client/admin/logistics-map-loader.test.ts
• TODO.md