Add a conformance suite for HermitCrab, with its adequacy argument

[johnml1135]

Quick summary

Parser maintainers can compare full parse signatures across HermitCrab and compatible engines.
The suite covers 44 fixtures and 536 cases with explicit expectations and auditable coverage evidence.
It leaves HermitCrab's analysis and synthesis algorithms unchanged.

Where to look

• conformance/PROTOCOL.md -- engine adapter contract.
• conformance/generated/hc-conformance-manifest.v1.json -- fixture paths and hashes.
• src/SIL.Machine.Morphology.HermitCrab.Conformance/SemanticCoverage/AnalyzerMetadataInspector.cs -- hash-pinned generator admission remains probe-gated.
• src/SIL.Machine.Morphology.HermitCrab.Conformance/MaterializedRunner.cs -- crash fixtures require an ordinary fixture to complete.

Deliberately not included

• Counterfactual and coverage-evidence sweeps remain deferred; known oracle gaps are tracked.

Validation

• dotnet build and dotnet build -c Release -- succeeded, 0 warnings.
• dotnet test tests/SIL.Machine.Morphology.HermitCrab.Tests --no-build -- 593 passed, 1 skipped (symlink test needs elevation), 0 failed.
• dotnet run --no-build -c Release --project src/SIL.Machine.Morphology.HermitCrab.Conformance -- --fixtures conformance -- 43 passed, 0 failed.
• ... -- --semantic-coverage --repository-root . -- 0 new gaps, 0 stale lines.
• python conformance/parity-check.py -- all checks passed.
• dotnet csharpier check . -- 868 files, clean.
• pwsh -NoProfile -File scripts/comment-hygiene.ps1 -BaseRef origin/master -- clean.

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Decisions, and why

• PCRE.NET (now on master) ships an IIncrementalGenerator. The compilation-graph loader admits it only by content hash, and a probe runs it and fails closed on any generated output.
• An expect_crash fixture passes only if the same engine completes an ordinary fixture in the same run, so a broken adapter command cannot pass as a crash (conformance/PROTOCOL.md).
• *.fwdata is marked binary in .gitattributes; its pinned hash depended on core.autocrlf, which is why CI failed a test that passed locally.
• Hand-maintained fixture totals were removed from the README and docs; the manifest is the count.
• Four fixture grammars keep trailing whitespace: their hashes are pinned in the manifest.

🤖 Generated with Claude Code

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This change is 

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.08%. Comparing base (c7146cd) to head (18cf242).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #480      +/-   ##
==========================================
- Coverage   74.34%   74.08%   -0.27%     
==========================================
  Files         456      555      +99     
  Lines       38261    55976   +17715     
  Branches     5242     7606    +2364     
==========================================
+ Hits        28445    41468   +13023     
- Misses       8666    12658    +3992     
- Partials     1150     1850     +700     

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[johnml1135]

Added two independently justified conformance fixtures in a20bce1: final-template-partial-discriminators (10 words; #507) and template-category-sharing (6 words; #505). Fresh Release build: zero warnings/errors. Both fixtures pass with memoization on and off, zero skipped; 22 focused manifest/coverage tests pass. Four grammar counterfactuals produce the independently predicted mismatches, documented under conformance/docs. These are grammar-sensitivity controls, not proof that pruning, cache hits, or same-key feature collisions execute. No parser code changed. Generated inventory also restores previously omitted rows for the already-existing Exact-inverse fixture; its valid zudiua loss remains tracked in #504, not relabeled as correct.

[johnml1135]

Added the shared-template unconstrained-suffix conformance fixture in f150e2a. The grammar has a slot-only feature-unconstrained suffix shared by mandatory TV/IV templates, an ordinary N-to-IV verbalizer, four positive rows, and six rejection controls. The companion rationale explains complete forward derivations and loader reachability (not a FieldWorks UI round trip).

Fresh C# harness: all 10 rows pass in both template orders, memoization on/off (40 comparisons; no skips). Focused template/manifest tests: 22 passed, no skips. Regenerated manifest is current at 40 fixtures; coverage/rule reports updated. No Machine parser code changed.

PanGloss main now contains the narrow gate-only alignment (fc357daf), with this fixture mirrored unchanged until its old Machine submodule pin is upgraded. Direct state assertions provide red/green evidence; full-parse fixture checks pass both before and after the change. Issue #505 remains open for collision/correlation and broader merge-equivalence evidence.