fix(fixtures): give the Acta set a policy digest that is actually current

[lywinged]

Follows up the second half of my review on #98, which nobody had a chance to answer before it merged. Small, and it is fixture data plus the checks over it: no spec text, no schema, no record field.

cc @tomjwxf, since this touches your set.

What is wrong

All six fixtures carry the same policy_digest, and none of them equals current_policy_digest in expected.json:

current_policy_digest              sha256:bda8d8f6...
01-valid-accepted.json             sha256:b5af974a...  != current   declared=pass
02-valid-denied.json               sha256:b5af974a...  != current   declared=pass
03-signature-key-mismatch.json     sha256:b5af974a...  != current   declared=n/a
04-broken-chain.json               sha256:b5af974a...  != current   declared=pass
05-stale-policy-digest.json        sha256:b5af974a...  != current   declared=fail
06-session-binding-mismatch.json   sha256:b5af974a...  != current   declared=pass

distinct policy_digest values across all six: 1

By the comparison the README states for 05 — "policy_digest names a policy bundle that is no longer the one in force (current_policy_digest in expected.json)" — 01, 02, 04 and 06 fail it too while being declared pass. issued_at does not rescue them: there is no validity window in the payload, and the stated check is a digest comparison.

That lands on what the set is for. The README says 04, 05 and 06 "make one point three ways", but on the freshness axis 05 was indistinguishable from every other fixture, and a second implementation running expected.json as the portable contract disagrees with it on four of six.

The cause, and the fix

decisionPayload() hardcoded POLICY_V1 with no override, so r05 got V1 like everything else — even though the comment directly above it says V1 is what makes 05 stale. The intent was in the comment; the code did not carry it out.

-function decisionPayload({ tool, decision, reason, sessionId, issuedAt, prevHash }) {
+function decisionPayload({ tool, decision, reason, sessionId, issuedAt, prevHash, policyDigest = POLICY_V2 }) {
     ...
-    policy_digest: POLICY_V1,
+    policy_digest: policyDigest,

 const r05 = envelope(decisionPayload({
   tool: 'run_shell', decision: 'allow', sessionId: SESSION,
   issuedAt: '2026-07-08T09:00:12.000Z',
+  policyDigest: POLICY_V1, // the only fixture carrying the superseded policy
 }), SIGNER_PRIV);

Everything downstream follows on its own, because envelopeHash(r01) is computed rather than pinned: signatures change, the chain head moves from 99c36f17 to ddf7efb0, and 02 and 04 relink automatically, with 04's deliberately wrong pointer staying deliberately wrong. 05 is byte-identical to before.

Before touching anything I ran the generator unmodified and confirmed it reproduces every committed file byte for byte, so the regenerated output can be trusted rather than assumed.

Why nothing caught it, and what does now

The generator's self-check asserted that 05 fails freshness and 06 fails binding, and nothing about the other four. Asserting the failure alone passes whether one fixture is stale or all six are. That asymmetry is the whole bug.

• gen.mjs now checks both axes for every fixture against the manifest, skipping only n/a.
• tests/test_acta_fixtures.py read the policy_freshness and session_binding declarations nowhere at all. The two tests that existed were hardcoded to one fixture each and asserted inequality, which passes either way. Replaced with parametrized tests over every fixture; on the pre-fix data they fail for exactly 01, 02, 04 and 06, which I checked rather than assumed.
• The crosswalk quotes 01 in full and says its chain_head "is real". Both went stale the moment the fixtures were regenerated, and nothing would have noticed. Resynced, and a test now pins the document against the fixtures.

Also dropped: the generator note saying freshness for 01/02/04/06 was "pass relative to their v1-era chain context in the docs narrative". The manifest no longer needs it, and it was never written into expected.json, so the portable contract carried those four declarations with nothing qualifying them.

Checks

214 passed, 1 skipped. ruff check src tests and mypy src/agentrust_trace clean.

Unchanged and worth repeating from the review: the hand-rolled canonicalize() in gen.mjs is correct. I differential-tested it against rfc8785 over ASCII, non-ASCII values, supplementary-plane values, supplementary-plane keys, nested arrays, large integers, floats, exponent-form floats, empty containers and escape sequences — identical bytes in every case. That is by construction rather than luck, since JCS is defined in terms of ECMAScript.

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[imran-siddique]

Checked the fixtures directly rather than reading the table: on this branch, 01, 02, 03, 04 and 06 now equal current_policy_digest, and 05-stale-policy-digest.json keeps the old value, which is the whole point of that fixture. Suite passes, 214.

The defect is worth naming precisely, because it is the kind that makes a conformance set actively misleading rather than merely incomplete: five fixtures declared pass while failing the exact comparison the README defines for 05. A set where the negative case is indistinguishable from the positives does not test what it says it tests, and a downstream implementer calibrating against it would have concluded the stale-policy check was unimplementable.

Generating the digest from the same source as expected.json in gen.mjs rather than a POLICY_V1 constant is the part that stops it recurring.

Merging both this and #136.