Record folded-booking line 381 dayCount equivalent

[stefan-burke]

What changed

Records the last mutation equivalent for src/features/api/folded-booking.ts in scripts/mutation/equivalent-mutants.txt, bringing the mutation score to 100% (58 killed, 5 suppressed, 0 survivors).

Why

PR #1913 was merged before this final commit landed. The line 381 mutant (dayCount: 1 → 0 in the FoldBase) is provably equivalent: childDaysFromParent uses dayCount only in the customisable_days branch, which processParentApiBooking rejects before reaching the fold. For daily parents the function returns clampDurationDays(parent.duration_days), and for standard parents it returns 1 (the standardValue) — neither reads dayCount, so 1 and 0 produce the same output for every reachable input.

Without this recording on main, the next precommit:mutation run on a folded-booking.ts change would report line 381 as a survivor.

Checks

• nix develop -c deno task mutation:audit-equivalents — all 438 equivalents valid.
• nix develop -c deno task mutation on folded-booking.ts — 100% (58/58 killed, 5 suppressed).
• nix develop -c deno task precommit — green.

Summary by CodeRabbit

• Documentation
  • Updated mutation coverage notes to reflect complete test coverage for folded booking behavior.
  • Documented an additional equivalent mutation and clarified that no unsuppressed mutation survivors remain.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 4df9bfc2-8a3e-4976-a7c6-3769e53c6d3e

📥 Commits

Reviewing files that changed from the base of the PR and between 4cb2f45 and 026667a.

📒 Files selected for processing (1)

• TODO.md

📝 Walkthrough

Walkthrough

Mutation tracking documentation now records the folded-booking mutant at line 381:17 as equivalent and updates the TODO entry to state that all mutants are covered, with five known equivalents.

Changes

Mutation coverage records

Layer / File(s)	Summary
Record folded-booking mutation equivalence scripts/mutation/equivalent-mutants.txt, TODO.md	Adds the folded-booking base.dayCount equivalent mutant and updates the TODO entry to report full mutation coverage with five recorded equivalents.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• chobbledotcom/tickets#1898: Related mutation-equivalence audit and registry updates.
• chobbledotcom/tickets#1910: Related changes to known-equivalent mutant records.
• chobbledotcom/tickets#1913: Related folded-booking mutation-equivalence documentation.

🚥 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 is concise and accurately highlights the main change: recording the folded-booking line 381 dayCount equivalent mutant.
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 unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch split/line-381-equivalent

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch split/line-381-equivalent

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[coderabbitai]

Actionable comments posted: 1

🤖 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 `@TODO.md`:
- Around line 1402-1405: Update the TODO entry describing the folded-booking
mutation tests to distinguish test-killed mutants from the five suppressed
equivalent mutants, stating that the tests kill every non-equivalent mutant
while preserving the existing proof and survivor details.

🪄 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: f349f8d7-3b87-4819-808e-cdf83c296c1f

📥 Commits

Reviewing files that changed from the base of the PR and between de18887 and 4cb2f45.

📒 Files selected for processing (2)

• TODO.md
• scripts/mutation/equivalent-mutants.txt