[drk-ram]

What

Canonicalize TRACE claim signing inputs, claim digests, and tool catalog/definition SHA-256 hashes with RFC 8785 (JCS) instead of json.dumps(..., ensure_ascii=True).

Why

json.dumps(..., sort_keys=True, separators=(",", ":")) defaults to ensure_ascii=True, escaping non-ASCII UTF-8 code points to \uXXXX and formatting floating-point values using Python's repr rather than RFC 8785 Section 3.2.2.3. That caused TRACE claims and catalog hashes containing non-ASCII or float values to diverge from JCS verifiers.

Closes #837

Security impact

Restores RFC 8785 (JCS) canonicalization across cmcp_runtime.audit.trace_claim, cmcp_runtime.catalog.loader, cmcp_runtime.session.manager, and cmcp_verify, preventing cross-verifier signature and digest mismatches on non-ASCII or numeric claims.

Test plan

• pytest passes (pytest tests/unit/test_trace_claim.py tests/unit/test_catalog_jcs_hashes.py tests/unit/test_session_manager.py tests/unit/test_kill_switch.py tests/unit/test_verify.py — 165 passed)
• ruff check passes (ruff check src tests — passed)
• mypy passes (mypy src — passed)
• Manual test performed (describe steps below if applicable)

DCO sign-off

• My commits include Signed-off-by: (git commit -s)

[github-actions]

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