Expand parity harness coverage before behavioral drift lands

The landed mock Anthropic harness now covers multi-tool turns, bash flows,
permission prompt approve/deny paths, and an external plugin tool path.
A machine-readable scenario manifest plus a diff/checklist runner keep the
new scenarios tied back to PARITY.md so future additions stay honest.

Constraint: Must build on the deterministic mock service and clean-environment CLI harness
Rejected: Add an MCP tool scenario now | current MCP tool surface is still stubbed, so plugin coverage is the real executable path
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep rust/mock_parity_scenarios.json, mock_parity_harness.rs, and PARITY.md refs in lockstep
Tested: cargo fmt --all
Tested: cargo clippy --workspace --all-targets -- -D warnings
Tested: cargo test --workspace
Tested: python3 rust/scripts/run_mock_parity_diff.py
Not-tested: Real MCP lifecycle handshakes; remote plugin marketplace install flows

rust/MOCK_PARITY_HARNESS.md

@@ -17,6 +17,11 @@ The harness runs these scripted scenarios against a fresh workspace and isolated
 3. `grep_chunk_assembly`
 4. `write_file_allowed`
 5. `write_file_denied`
+6. `multi_tool_turn_roundtrip`
+7. `bash_stdout_roundtrip`
+8. `bash_permission_prompt_approved`
+9. `bash_permission_prompt_denied`
+10. `plugin_tool_roundtrip`
 
 ## Run
 
@@ -25,6 +30,15 @@ cd rust/
 ./scripts/run_mock_parity_harness.sh
 ```
 
+Behavioral checklist / parity diff:
+
+```bash
+cd rust/
+python3 scripts/run_mock_parity_diff.py
+```
+
+Scenario-to-PARITY mappings live in `mock_parity_scenarios.json`.
+
 ## Manual mock server
 
 ```bash