Enforce abstract reasoning posture during bundle validation

[mdheller]

This PR adds the actual runtime enforcement for the abstract reasoning gate in bundle validation.

Why:

• abstract and program-induction lanes should not pass validation on llm-only posture
• validation should require declared verification mode and required evidence refs when policy says so
• ControlGateArtifact and ValidationArtifact should surface abstract-lane posture explicitly

What this PR changes:

• patches scripts/evaluate_control_matrix_gate.py
• patches scripts/validate_bundle.py
• enforces abstract reasoning posture before execution eligibility
• exposes abstract gate posture in the validation artifact

What this PR does not do:

• it does not yet extend execution-time artifacts
• it does not yet add runtime-side postcondition/divergence emitters

[mdheller]

Cross-repo dependency map for this runtime-enforcement slice:

• semantic artifact refs: Add abstraction-verification artifacts for program candidates and counterexamples semantic-serdes#5
• planning transport/contracts: Add planning-service contracts for program induction, counterexample search, and backtracking TriTRPC#38
• benchmark doctrine and result contracts: Add abstract reasoning evaluation standard and benchmark contracts socioprophet-standards-storage#62
• authored abstract admissibility policy: Add abstract branch admissibility policy contract policy-fabric#10
• first consumer pilot: Add abstract export repair planning pilot for HDT human-digital-twin#6
• runtime gate semantics note in this repo: Document abstract reasoning gate semantics for validation-time enforcement #28

Suggested merge order:

1. semantic-serdes Workflow: harden PR helper #5
2. TriTRPC feat: add SourceOS Asahi stage bundle #38
3. standards-storage #62
4. policy-fabric Seed control matrix v3 import lane #10
5. agentplane Document abstract reasoning gate semantics for validation-time enforcement #28 then Enforce abstract reasoning posture during bundle validation #31
6. human-digital-twin Execution evidence hardening: run/replay artifacts and sociosphere bridge #6

This PR is the point where the abstract lane becomes enforceable at bundle-validation time rather than only documented upstream.