Align CBM serialized form with declared schema

[GiggleLiu]

Summary

ConsecutiveBlockMinimization's ProblemSchemaEntry::fields declares only matrix and bound, but the model's serde was inconsistent with that declaration:

• Serialize wrote 4 fields (matrix, num_rows, num_cols, bound) via the default field-by-field derive
• Deserialize (via try_from = ConsecutiveBlockMinimizationDef) required num_rows and num_cols to be present, even though they're fully derivable from matrix

That inconsistency broke the schema-driven pred create path: it builds JSON from the declared schema fields (matrix + bound), then validates by deserializing — which failed with Schema-driven factory rejected generated data for ConsecutiveBlockMinimization: missing field 'num_rows'. Reproducer:

$ pred create CBM --matrix '[[true,false,true],[false,true,true]]' --bound-k 2
Error: Schema-driven factory rejected generated data for ConsecutiveBlockMinimization: missing field `num_rows`

Fix

num_rows and num_cols are just matrix.len() and matrix[0].len() — they're cached for fast getter access but they're not independent data. Drop them from the wire format entirely by adding serde(into = ConsecutiveBlockMinimizationDef) so both directions round-trip through the minimal {matrix, bound} form. try_new already recomputes the cached dimensions on construction.

The previous validation that "if the JSON contains a num_rows that disagrees with the matrix, reject" was guarding against malformed input we shouldn't have been producing in the first place; the real input validation that survives is ragged-matrix rejection (in validate_matrix_dimensions), which is now what the test suite exercises.

Verification

$ pred create CBM --matrix '[[true,false,true],[false,true,true]]' --bound-k 2 \
    | pred solve - --solver brute-force
{
  "evaluation": "Or(true)",
  "problem": "ConsecutiveBlockMinimization",
  "solution": [0, 2, 1],
  "solver": "brute-force"
}

Test plan

• cargo test --lib — 4958 passed (9 CBM-specific tests pass)
• cargo test --test main — 75 integration tests passed
• cargo fmt --all -- --check
• cargo clippy --all-targets --workspace -- -D warnings
• Manual end-to-end: pred create CBM ... | pred solve returns Or(true) with witness [0, 2, 1]

Related

• Switch broken CBM example in README to MIS #1064 swaps the README's broken CBM example for an MIS one. With this PR landed, the original CBM example would also work; Switch broken CBM example in README to MIS #1064 still stands on its own merits (MIS is a more recognizable lead example).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.92%. Comparing base (cbfad84) to head (61db3c7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1065   +/-   ##
=======================================
  Coverage   97.92%   97.92%           
=======================================
  Files         966      966           
  Lines      100043   100044    +1     
=======================================
+ Hits        97967    97971    +4     
+ Misses       2076     2073    -3     

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