Wire Cedar into the cross-operator delegation example

[carloshvp]

Summary

• Pin cedarpy to the verified 4.8.7 API.
• Load policy.cedar into CedarPolicy in the cross-operator demo and test the shipped policy's allow and deny decisions.

Root cause

The demo treated policy.cedar as documentation and gave enforcement to a duplicate LocalPolicy allow-list. The cedarpy>=4.8 range also allowed the runtime and tests to resolve against a future incompatible API.

Impact

The example now evaluates the policy it ships. The delegated task:read capability passes the Cedar check, while Cedar denies task:write. The change keeps the existing software-asserted attestation labels.

Validation

• pytest tests/unit/ tests/conformance/ -q --cov=src --cov-report=term-missing (202 passed, 93.82% coverage)
• mypy src/ca2a_runtime/ src/ca2a_verify/
• ruff check src/ tests/
• bandit -q -r src/ -c pyproject.toml
• pip-audit (no known vulnerabilities)
• python examples/cross-operator-delegation/demo.py (12/12)

Closes #45

[imran-siddique]

The change itself reads well and it is the right direction: loading policy.cedar into CedarPolicy and actually evaluating the rule, rather than mirroring it with a LocalPolicy allow-set, removes a stand-in that made the example weaker than it looked. The README and transcript updates match what the code now does, and CI is green on this branch.

Only blocker is a merge conflict in pyproject.toml, and it is my fault rather than yours. main moved under you twice today: #69 moved the extension URI and maintainer email off agentrust.io, and #71 bumped the agentrust-trace pins for the TRACE v0.2 cutover. Both touched the dependency block you are editing.

It should be a mechanical resolution: keep your Cedar dependency addition, take main's versions for agentrust-trace (>=0.5) and agentrust-trace-tests (>=0.4,<0.5). Happy to push the rebase for you if you would rather not deal with a conflict you did not cause, just say so.

One unrelated note in case you hit it: tests/unit/test_cedar.py can fail locally on around six tests while passing in CI. That is an environment difference rather than your code, and CI here is clean.

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[carloshvp]

@imran-siddique I rebased this onto current main and resolved the pyproject.toml conflict in 3c3cdd7. The branch keeps cedarpy==4.8.7 and takes the current TRACE constraints: agentrust-trace>=0.5 and agentrust-trace-tests>=0.4,<0.5.

Local validation completed with 212 passed and 3 skipped, plus mypy, Ruff, Bandit, pip-audit, and all 12 demo scenarios. GitHub reports the branch mergeable with all required checks green.

Could you re-review when available?