feat(policy): classify raw extension proposals as untrusted

[seonghobae]

Partial implementation of #27, stacked on PR #76.

Buyer/security gap

PR #76 composes exact extension proposal authority with ordinary action policy, but it accepts an already-constructed ActionRequest. A raw extension-message adapter must not be able to construct that request with InstructionSource::User or EnterprisePolicy merely because extension transport delivered the message, and it must retain the parent’s current origin and trusted-time/expiry authority checks.

Live dependency / stack state

This Draft is stacked on current exact PR #76 head fc9c7348d367a0b6295d8e2f0289b0262ef3675f. Current exact contributor head is 663eb89c55cf6c2505c2cc115b491bda49d89bf5.

Fresh exact compare is ahead 10 / behind 0, with merge base exactly equal to the live prerequisite. Relative to #76 the child delta is limited to:

• CHANGELOG.md;
• crates/originweave-policy/src/lib.rs; and
• crates/originweave-policy/tests/extension_message_action_proposal.rs.

Keep Draft while #76/#74 remain active. No prerequisite check, review, status, coverage, mergeability, or predecessor result transfers to this child.

TDD / dependency repair lineage

1. Original test-only head dbe06efc006fda316201ba295af4b933a4b41f14 established the missing raw-message trust boundary before production exposed it.
2. Production introduced ExtensionMessageActionProposal and evaluate_extension_message_action_proposal so raw extension-produced message content has no instruction-source selector and is internally classified as InstructionSource::WebContent.
3. The live feat(policy): compose extension proposals with action policy #76 prerequisite later advanced its extension-access contract to bind proposal authority to request source origin plus caller-supplied trusted current time and exclusive grant expiry. The old child 0579e7a27c6dadd56b653938ed0fcd1ff08fef93 had diverged from the new parent: exact compare from live feat(policy): compose extension proposals with action policy #76 to that child was ahead 5 / behind 8 with an obsolete merge base.
4. This branch was repaired non-destructively rather than abandoned or force-rebased. The current parent tree was merged into the existing canonical child, then only the child-owned raw-message boundary was reconstructed on top of the current parent API.
5. Focused regressions now additionally prove that a raw extension message cannot reuse a proposal grant for another source origin and cannot reuse an expired grant. The existing missing-grant, untrusted-instruction, and secret-material regressions remain intact.
6. CI on reconstruction head 581ff56d91212b12c66ce9e20a95442a7949924f reached full tests/Clippy/rustdoc behavior but exposed only canonical rustfmt import wrapping. Current head 663eb89c55cf6c2505c2cc115b491bda49d89bf5 applies only that formatting correction; no authority or evidence gate was weakened.

Implemented boundary

ExtensionMessageActionProposal and evaluate_extension_message_action_proposal now:

• carry typed action, source/target origin, secret-delivery metadata, and immutable intent digest but expose no instruction-source selector;
• require exact extension identity, browser session, browsing context, proposal capability, proposal source origin, and trusted current time through the existing feat(policy): compose extension proposals with action policy #76 composition boundary;
• fail closed when the proposal grant is absent, mismatched, bound to another origin, or expired;
• construct the ordinary ActionRequest internally with InstructionSource::WebContent;
• preserve the proposal’s action/origin/secret/digest fields unchanged when delegating to ordinary policy; and
• therefore prevent extension-produced message content from minting human or enterprise instruction trust merely because extension transport delivered it.

now_epoch_seconds remains a trusted caller input; extension/page content cannot provide or attest it through this API.

Exact-current GREEN evidence

On unchanged exact head 663eb89c55cf6c2505c2cc115b491bda49d89bf5 against unchanged exact prerequisite fc9c7348d367a0b6295d8e2f0289b0262ef3675f:

• ancestry: ahead 10 / behind 0, merge base exactly the live prerequisite;
• CI run 32084014823: success;
• Rust contracts job 95552634445: repository contracts, canonical formatting, locked workspace/all-target check, full tests, strict Clippy, and rustdoc success;
• Production coverage job 95552634441: exact owned-production function, line, region, and branch measurement and enforcement success;
• exact combined commit status returns CodeRabbit success;
• formal reviews currently returned: none; and
• inline review threads currently returned: none.

Security Scan, SAST, and central OpenCode/Noema/Strix/required-workflow evidence are not returned for this exact stacked head and are therefore absent, not passing. No predecessor, prerequisite, pre-reconstruction, queued, skipped, cancelled, absent, synthetic-merge, stale, status-only, or model-only evidence is promoted as current proof.

Truth boundary / remaining #27 work

A separately trusted future adapter may authenticate independent user or managed-policy provenance through a different explicit boundary. This lane does not parse Chromium extension messages, establish transport sender authenticity beyond the existing extension/session/context/origin/time grant, execute browser input, resolve secrets, verify post-conditions, persist managed-extension policy, or complete issue #27.

This scheduled actor does not merge, self-approve, alter workflows, add secrets, weaken checks, tag, or publish.

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