toolchain: batch example-case validation in precheck (~7x faster)

[sbryngelson]

What

./mfc.sh precheck's example-case step (check 7/7) ran ./mfc.sh validate once per case in a serial loop over all 155 examples/*/case.py. Each invocation re-paid the mfc.sh/venv bootstrap (~2.4s), which dominated (~90%) the ~6.5 min serial cost of that step.

validate now accepts multiple case files (nargs="+") and validates them all in one process: load + constraint-check each, failing only on a genuine load/parse error — matching the historical per-file exit behavior (a single ./mfc.sh validate exits non-zero only on a load error; constraint issues are warnings). precheck.sh calls ./mfc.sh validate examples/*/case.py once instead of looping.

Impact

	Before	After
Full precheck (idle node)	~394 s	~56 s (~7×)
Example-case step	155 serial validate calls	1 batched call, 155/155 in one process

Correctness is unchanged — all 155 cases are still loaded and constraint-checked; only the process/bootstrap overhead is removed. The single-file ./mfc.sh validate case.py path is untouched.

Changes (4 files, +52/−14)

• toolchain/mfc/validate.py — _validate_batch() for the multi-file path
• toolchain/mfc/cli/commands.py — validate positional gains nargs="+"
• toolchain/mfc/args.py — abspath loop handles the list case
• toolchain/bootstrap/precheck.sh — step 7 is a single batched validate call

Validation

Full precheck green (all 7 checks) — the commit's own pre-commit hook prechecked itself in ~56 s. Batch validates 155/155 example cases in one process.

[Copilot]

Pull request overview

This PR speeds up ./mfc.sh precheck by batching validation of all examples/*/case.py files into a single ./mfc.sh validate invocation, avoiding repeated toolchain/venv bootstrap overhead while preserving the historical “only fail on load/parse errors” behavior.

Changes:

• Add a multi-file validation path in toolchain/mfc/validate.py to load and constraint-check many cases in one process.
• Update the CLI to accept one or more positional input files (nargs="+") and normalize them to absolute paths.
• Change precheck.sh example-case validation step from a per-case loop to a single batched validate call.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
toolchain/mfc/validate.py	Adds _validate_batch() and routes multi-file inputs through it.
toolchain/mfc/cli/commands.py	Changes validate positional input to accept multiple files (nargs="+").
toolchain/mfc/args.py	Converts input to absolute paths when it is a list (multi-file validate).
toolchain/bootstrap/precheck.sh	Replaces serial per-case validate loop with one batched validate invocation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.07%. Comparing base (102def2) to head (55b3562).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1634      +/-   ##
==========================================
+ Coverage   60.88%   61.07%   +0.18%     
==========================================
  Files          83       83              
  Lines       19836    19925      +89     
  Branches     2953     2975      +22     
==========================================
+ Hits        12077    12169      +92     
+ Misses       5767     5753      -14     
- Partials     1992     2003      +11     

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