fix(bc): rotated free-slip zero-datum guard compares by value (#336)

[lmoresi]

Closes#336.

The bug (found by Wave E's WE-09 sweep, filed as #336)

The Wave C shim's zero-datum guard in SNES_Stokes_SaddlePt.add_rotated_freeslip_bc used sympy.sympify(conds) != 0 — a structural comparison, so Float(0.0) != Integer(0) is True. The canonical value-first call add_rotated_freeslip_bc(0.0, boundary) — the exact form the method's own deprecation message recommends — raised NotImplementedError, while conds=0 (int) worked. Legacy boundary-first calls were unaffected (they pass conds=None); the bug bit exactly the users adopting the migration #334 asks for.

The fix

sympy.sympify(conds).is_zero is not True — value semantics. is_zero is True only when sympy can prove zero, so every numeric zero form (0.0, Float(0), S.Zero, Integer(0)) is accepted and an unprovable symbolic datum (Symbol('a')) is still rejected.

Verification

• New regression tests in test_0641 (zero forms accepted warning-free; symbolic still raises) — shown failing against the unmodified build first (1 failed / 6 passed), 42/42 after.
• level_1 and tier_a: 371 passed / 10 skipped / 2 xfailed / 1 xpassed (baseline 369 + the 2 new tests; nothing lost). Clean rm -rf build/ pyx rebuild.
• No dependency/lockfile changes.

Sequencing note

PR #338 (Wave E) carries a TODO(BUG) marker on this same guard line — merge #338 first; I will refresh this branch over it (removing the marker) so the diff stays one logical change.

Underworld development team with AI support from Claude Code

[Copilot]

Pull request overview

Fixes a Wave C API-shim regression in SNES_Stokes_SaddlePt.add_rotated_freeslip_bc where the “zero datum” guard used SymPy structural comparison and incorrectly rejected conds=0.0 (and other numeric-zero representations) in the canonical value-first call order.

Changes:

• Update the zero-datum guard to use value semantics via sympy.sympify(conds).is_zero is not True, accepting all provable numeric zeros while rejecting unprovable symbolic data.
• Add regression coverage ensuring numeric-zero forms are accepted without deprecation warnings and symbolic data still raises NotImplementedError.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/test_0641_wave_c_api_shims.py	Adds regression tests covering numeric-zero acceptance and symbolic rejection for add_rotated_freeslip_bc in value-first order.
src/underworld3/cython/petsc_generic_snes_solvers.pyx	Fixes the rotated free-slip zero-datum guard to compare by value (is_zero) rather than structural equality.

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[lmoresi]

Second commit added: the two Copilot review comments on #334 (shim TypeError said "positionally" on keyword calls; DeprecationWarning always described the legacy form as (boundary, g=...)) are fixed here — each message now names the legacy form the caller actually used, with contract tests pinning all three legacy shapes. Gate: 373 passed (baseline 369 + 4 new tests), clean pyx rebuild.

Underworld development team with AI support from Claude Code