fix(ci): preserve recipe failure diagnostics

[martin-kolinek]

🤖 Fixes CI failures whose useful recipe output could be obscured by a later synthetic failure step. This was exposed by the Windows coverage gate in run 33158834495, where cargo-gamma-rt measured 90.7% against a 90.8% threshold but the failed step did not present that diagnosis clearly.

Changes

• propagate Just's captured exit status from the same step that streams the complete recipe output
• remove the synthetic follow-up failure step
• add exact coverage counts, uncovered source ranges, and explicit no-data diagnostics to cargo-coverage-gate output
• run PR and scheduled Codecov uploads under always() when LCOV reports exist
• retain the Windows ARM exclusion and avoid empty uploads
• update generated workflows, design documentation, tests, and snapshots

Validation

• cargo-anvil GitHub artifact unit tests
• cargo-anvil generated-workflow snapshot tests
• actionlint validation for emitted workflows
• cargo-anvil Clippy with warnings denied
• cargo-coverage-gate unit and CLI tests
• formatting, generated README, and spelling checks

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.6%. Comparing base (2937b1b) to head (57e4a5a).

❌ Your project status has failed because the head coverage (97.6%) is below the target coverage (100.0%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@          Coverage Diff           @@
##            main    #110    +/-   ##
======================================
  Coverage   97.6%   97.6%            
======================================
  Files        290     291     +1     
  Lines      65913   66055   +142     
======================================
+ Hits       64369   64514   +145     
+ Misses      1544    1541     -3     

Flag	Coverage Δ
linux	97.6% <100.0%> (?)
linux-arm	97.6% <100.0%> (?)
windows	97.8% <100.0%> (?)

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[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[Sander Saares (sandersaares)]

[Copilot speaking]

Published 9 findings. No finding follows up on an existing discussion thread.

See diagnostics

Diagnostic	Value
Cache	Hit

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 23 out of 24 changed files in this pull request and generated no new comments.

[Copilot]

🟡 Changes recommended

The new implementation guide contains an inaccurate invariant description (it attributes line ordering to the parser’s map rather than the now-explicit sorting) that should be corrected to match the current behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 23/24 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes consistently preserve failure diagnostics at the correct step boundary and the new coverage-gate diagnostics are deterministic, bounded, and covered by updated tests/snapshots.

Review details

• Files reviewed: 23/24 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes consistently preserve CI diagnostics while adding deterministic, bounded coverage failure details with corresponding tests/docs and no evident correctness or integration issues in the reviewed diffs.

Review details

• Files reviewed: 23/24 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes are cohesive, deterministically implemented, and backed by updated unit/CLI/snapshot coverage that exercises the new diagnostic and CI-failure-propagation behavior.

Review details

• Files reviewed: 23/24 changed files
• Comments generated: 0 new
• Review effort level: Lite