Local validation API: execution-model-aware profiles

[zkwentz]

What & Why

Authors need the same planner/executor contract for fast source checks and runtime API checks. This PR implements execution-model-aware local profiles and runtime probing, replacing the legacy validation split.

Risk & Review Guidance

• Risk level: MEDIUM — changes local validation behavior and runtime launch paths
• Task class: feature
• Review focus: src/openenv/validation/local.py:411 for profile dispatch and launch; src/openenv/validation/runtime_probe.py for API probing; deletion in src/openenv/cli/_validation.py for legacy compatibility
• Blast radius: Regressions affect local author feedback and may leave launched processes behind.

Decisions & Alternatives

• Dispatch by execution model — rejected forcing one-shot subjects through served HTTP checks.
• Trusted source may launch locally — untrusted source must instead use an already isolated URL or later remote mode.
• One shared report — legacy output is adapted rather than maintaining two semantic validators.

Verification

• PASS: PYTHONPATH=src:envs .venv/bin/python -m pytest tests/ -q -m 'not integration' — 1,559 passed, 114 skipped, 31 external integration tests deselected on the complete stack.
• PASS: Fork whole-stack CI — 7/7 checks passed, including Python 3.11/3.12, lint, docs, lock validation, and package smoke tests.
• NOT verified: Optional heavy environment runtimes remain skipped when their dependencies are absent.

Scope & Non-Goals

• Local execution does not claim network enforcement, cross-host reproducibility, or certification.

Stack

PR 5 of 17; depends on #945.

Full 17-PR stack

1. #942 RFC 008: Spec-neutral local and remote validation architecture
2. #943 Validation foundation: spec-neutral contracts and adapters
3. #944 Validation policy: spec-aware check registry and planner
4. #945 Validation executor: hardened shared reports and eligibility
5. #946 Local validation API: execution-model-aware profiles ← current
6. #947 CLI: validation profiles and shared reports
7. #948 HF runtime: dedicated sandbox execution mode
8. #949 HF certification: enforce trusted dedicated isolation
9. #950 [RFC 008] Define remote author validation and publish gating
10. #951 Validation: unify CLI reports and add a strict publish profile
11. #952 Validation: add structured author diagnostics and remediation
12. #953 Validation: run author validation in dedicated HF Sandboxes
13. #954 Validation: isolate submitted code in author Sandboxes
14. #955 Validation: bind author reports to policy and source
15. #956 CLI: scaffold publish requirements
16. #957 CLI: gate pushes on staged remote validation
17. #958 Docs: explain local, remote, and publish validation

All upstream PRs remain draft while RFC 008 is under review.