test: add integration test for unlock happy path against mock contract - #592

Overview

This PR adds an integration test that exercises the challenge → sign → unlock happy path for the prompt-hash contract against a mocked has_access contract, guarding regressions in the unlock flow without depending on real access-control state.

Related Issue

Changes

🧪 Unlock Happy Path Integration Test

• [ADD] contracts/prompt-hash/src/mock_has_access.rs

  • Minimal mock contract exposing a controllable has_access function.
  • Returns true for the test signer so the unlock happy path can complete.

• [MODIFY] contracts/prompt-hash/src/test.rs

  • Adds challenge -> sign -> unlock integration test.
  • Asserts the full happy path succeeds end-to-end.
  • Verifies a denied has_access would cause the unlock to fail, protecting the regression guard.

• [MODIFY] contracts/prompt-hash/src/lib.rs

  • Wires the mock has_access contract into the test-only build.
  • Keeps production unlock behavior unchanged.

Verification Results

cargo test -p prompt-hash
✅ 3/3 passed

Integration acceptance check:
✅ challenge -> sign -> unlock completes successfully
✅ mock has_access authorizes the test signer
✅ unlock happy path is guarded against has_access regressions

Closes #450