refactor(flips)!: box nested FlipError payloads (#406)

[acgetchell]

• Box nested typed FlipError payloads and the inserted-simplex witness while keeping scalar and key diagnostics inline.
• Preserve typed inspection through Error::source, reason.as_ref(), and source.as_ref() for flip context, predicate, adjacency, simplex, neighbor-wiring, and mutation failures.
• Add repository Semgrep checks for the boxed-source policy and document the tooling rationale.
• Preserve padded changelog category headings during post-processing.

BREAKING CHANGE: FlipError variants carrying nested typed errors or inserted-simplex witnesses now store those payloads in Box, so direct constructors and pattern matches must use boxed payloads and inspect them through as_ref().

Closes #406

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• .codecov.yml
• justfile
• src/delaunay/construction.rs

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• .codecov.yml

---

Walkthrough

FlipError variants were converted to use boxed typed payloads and marked as sources; From impls and callers were updated to box reasons; runtime classification and many tests match boxed inner errors via reason.as_ref(); Semgrep rules, fixtures, justfile wiring, and docs were added; changelog heading parsing and codecov target adjusted.

Changes

FlipError Payload Boxing

Layer / File(s)	Summary
FlipError enum contract and boxing policy src/core/algorithms/flips.rs	FlipError variants and docs now box large/nested typed payloads (adjacency, context, predicate, neighbor wiring, mutation, simplex witness) and expose them as #[source] where appropriate.
Error construction and From conversions src/core/algorithms/flips.rs	Construction sites now return typed error .into() values and updated From<...> for FlipError impls wrap typed payloads in Box.
Runtime classification and matching src/core/algorithms/flips.rs, src/delaunay/construction.rs	Classification and failure-kind mapping inspect boxed reasons with reason.as_ref(); is_geometric_flip_error converted to non-const fn with equivalent pattern logic.
Behavioral tests updated for boxed shapes src/core/algorithms/flips.rs, src/delaunay/construction.rs	Tests updated to construct boxed reasons (Box::new(...)) and to pattern-match boxed payloads via ref reason + reason.as_ref() across mapping, rollback, and dynamic rejection tests.
Sizing and downcasting tests src/core/algorithms/flips.rs	New assertions check size/alignment invariants and that nested boxed typed payloads are recoverable via Error::source() downcasting; test imports adjusted for mem::size_of/align_of.

Semgrep Rule Enforcement & Tooling

Layer / File(s)	Summary
Semgrep rules for payload boxing enforcement semgrep.yaml	Added delaunay.rust.flip-error-nested-payloads-boxed and delaunay.rust.flip-error-boxed-payloads-are-sources to detect unboxed nested payloads and missing #[source] on boxed fields.
Test fixture with error enum definitions tests/semgrep/src/project_rules/rust_style.rs	Added FlipContextError, SimplexValidationError, and a representative FlipError with boxed payloads and #[source]/#[from] annotations to validate rule matching.
Semgrep test recipe and cleanup justfile	semgrep-test now creates per-fixture state_dir/state_root, symlinks semgrep.yaml per fixture, sets SEMGREP_SEND_METRICS=off, and runs semgrep scan --strict --config <config> <fixture> per fixture; cleanup updated.
Tooling docs docs/dev/tooling-alignment.md	Documented repository-owned Semgrep enforcement for FlipError layout policy (inline scalars/keys, boxed nested typed payloads).

Changelog & Coverage

Layer / File(s)	Summary
Boundary parsing normalization and test coverage scripts/postprocess_changelog.py, scripts/tests/test_postprocess_changelog.py	ATX heading detection now trims matched titles and returns False on non-matches; added test ensuring "### Fixed ###" preserves category heading normalization.
Patch coverage target .codecov.yml	Patch coverage target increased from 50% to 70%.

🎯 4 (Complex) | ⏱️ ~60 minutes

Possibly related PRs

• acgetchell/delaunay#407: Boxes DelaunayRepairError flip wrapper and updates source traversal logic; closely related to this PR's FlipError boxing and source handling.
• acgetchell/delaunay#363: Refactors flip failure taxonomy and FlipError→failure-kind conversions that interact with the boxed payload changes here.
• acgetchell/delaunay#391: Modifies FlipContextError variants used inside FlipError; overlaps with the boxed FlipContextError treatment.

"🐰 I boxed my errors, snug and tight,
So sources gleam in error-light.
Tests updated, semgrep nods with glee,
No hidden reasons hiding from me,
Hoppity hop — clean traces in sight!"

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: boxing nested FlipError payloads, which is the primary refactoring across multiple files.
Description check	✅ Passed	The description is directly related to the changeset, detailing the boxed payloads, preservation of typed inspection, Semgrep checks, and breaking changes.
Linked Issues check	✅ Passed	The PR successfully addresses all coding objectives from #406: boxed nested typed payloads while preserving scalars inline, typed inspection through Error::source and as_ref(), repository Semgrep enforcement, updated tests/docs, and measured size improvements with justified policy.
Out of Scope Changes check	✅ Passed	All changes are within scope: FlipError boxing (core objective), changelog postprocessing normalization (supporting doc infrastructure), Semgrep rules (policy enforcement), updated tests and construction logic, and Codecov threshold raise (CI hardening for policy validation).
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 100.00%.

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity

Metric	Results
Complexity	0

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🟢 Coverage 83.03% diff coverage · +0.03% coverage variation

Metric	Results
Coverage variation	✅ +0.03% coverage variation (-1.00%)
Diff coverage	✅ 83.03% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (289b9b7)	62863	56884	90.49%
Head commit (862766d)	63058 (+195)	57077 (+193)	90.52% (+0.03%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#435)	277	230	83.03%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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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 `@src/core/algorithms/flips.rs`:
- Around line 13776-13783: The test test_flip_error_boxes_nested_typed_payloads
uses ABI-dependent byte-size assertions on FlipError (size_of::<FlipError>() <=
48 and size_of::<Result<(), FlipError>>() == size_of::<FlipError>()); change
these to target-agnostic checks: remove hardcoded byte expectations and either
assert structural properties (e.g., that Result<(), FlipError> has the same
alignment/representation intent) or gate exact-size assertions behind
cfg(target_arch/target_pointer_width) so CI platforms don't fail; update the
test to reference FlipError and Result<(), FlipError> and use
platform-conditional checks or loosened bounds instead of fixed 48-byte
assertions.

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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

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Configuration used: Path: .coderabbit.yml

Review profile: CHILL

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📥 Commits

Reviewing files that changed from the base of the PR and between 289b9b7 and 0743aa2.

📒 Files selected for processing (8)

• docs/dev/tooling-alignment.md
• scripts/postprocess_changelog.py
• scripts/tests/test_postprocess_changelog.py
• semgrep.yaml
• src/core/algorithms/flips.rs
• src/delaunay/construction.rs
• src/delaunay/insertion.rs
• tests/semgrep/src/project_rules/rust_style.rs

[codecov]

Codecov Report

❌ Patch coverage is 83.03249% with 47 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.50%. Comparing base (289b9b7) to head (862766d).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/core/algorithms/flips.rs	81.52%	46 Missing ⚠️
src/delaunay/insertion.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #435      +/-   ##
==========================================
+ Coverage   90.48%   90.50%   +0.02%     
==========================================
  Files          71       71              
  Lines       62653    62848     +195     
==========================================
+ Hits        56689    56882     +193     
- Misses       5964     5966       +2     

Flag	Coverage Δ
unittests	90.50% <83.03%> (+0.02%)	⬆️

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