fix(specs): fall back only when ju is absent; let broken ju imports fail

[thorwhalen]

Closes #4.

Root cause

On the runner, ju==0.1.31 failed to import: ju/oas.py does import dill at module level and dill is not a declared dependency of ju. The bare except ImportError around the whole ju block in specs.py swallowed that, so CI only ever ran the basic fallback (CI coverage showed specs.py lines 97-108, the ju path, as missed). Reproduced in a clean venv: ju 0.1.31 raises ModuleNotFoundError: No module named 'dill'; ju 0.1.33 imports and generates specs correctly.

Change

• _import_func_to_form_spec(): only a missing ju / ju.rjsf falls back, emitting a visible JuNotInstalledWarning. Any other import failure (missing ju dependency, renamed symbol) propagates. The func_to_form_spec call itself is no longer inside a try block.
• ju>=0.1.33 floor (clean import; json_schema_to_signature's 'properties' branch ignores json_schema['required'] entirely ju#9 required-field handling).
• New tests take the ju path with no fallback guard: skip with a reason only when ju is absent, fail with the real traceback when ju is broken. Also tests for the fallback warning and for propagation.

Verified in three clean venvs: ju 0.1.33 → all pass; ju 0.1.31 → fails loudly on dill; no ju → 4 skipped with reason + warning.

Review

Adversarial review (fresh Opus subagent): no confirmed defects in the diff. It checked three venvs (ju 0.1.33, broken 0.1.31, no ju), reversed test order and isolation leaks; all clean. Findings acted on:

• Applied: an old ju without ju.rjsf, or a stray namespace ju/, fell back with a misleading warning. Only a missing top-level ju falls back now (2nd commit).
• Follow-ups: func_to_form_spec copies non-JSON-serializable defaults (Enum, date, object) into the schema ju#15 (non-JSON-serializable defaults → 500 on the spec route; now reached by everyone through the ju path), Surface a broken ju at app build time, not per request #8 (surface a broken ju at app build time; warning stacklevel through Mapping.get), param_to_prop_type is accepted but never passed to ju; *args/**kwargs become required string fields #9 (pre-existing: param_to_prop_type ignored, *args/**kwargs become required fields), Audit remaining broad except ImportError guards (pandas, pydantic, trans auto-register) #7 (other broad except ImportError guards).

Dependents gate: priv test-dependents uf (also -t): no dependents, so only uf's own suite ran. Its 38 doctest failures are identical to master's (pre-existing, #5). Repo tests/: 35 passed.

CI: ju 0.1.33 installed on the runner; ju tests ran (0 skipped); the ju branch of specs.py is now covered.

https://claude.ai/code/session_01UMu2bF25xcBqjScMKa7A3X