## Summary
This PR adds TDD bug-capture tests for bug #1079 (`project context set` missing `--execution-env-priority` flag). Per the Bug Fix Workflow in CONTRIBUTING.md, the first step in fixing any bug is to write a test that proves the bug exists.
### What was done
- **Behave unit tests** (6 scenarios in `features/project_context_set_exec_env_priority.feature`):
- `project context set --execution-env-priority override` with `--execution-environment` should succeed and persist
- `project context set --execution-env-priority fallback` with `--execution-environment` should succeed and persist
- `--execution-env-priority` without `--execution-environment` should be rejected
- Default to `fallback` when only `--execution-environment` is specified
- Invalid `--execution-env-priority` value should be rejected
- `project context show` should reflect persisted `execution_env_priority` in JSON output
- **Robot integration tests** (3 test cases in `robot/project_context_set_exec_env_priority.robot`):
- Override acceptance with persistence verification
- Fallback acceptance with persistence verification
- Full round-trip persistence check
All tests are tagged `@tdd_bug @tdd_bug_1079 @tdd_expected_fail`. The underlying assertions fail (confirming the bug exists — `--execution-env-priority` is "No such option"), and the `@tdd_expected_fail` tag inverts the result so CI passes.
### Bug confirmed
The `context_set()` function in `cleveragents.cli.commands.project_context` does not accept `execution_env_priority` as a parameter. The specification (§Execution Environment Routing, precedence table) requires this flag at precedence level 2 for project-level execution environment priority control.
### Quality gates
| Gate | Result |
|------|--------|
| `nox -s lint` | PASS |
| `nox -s typecheck` | PASS (0 errors) |
| `nox -s unit_tests` | PASS (12236 scenarios, 0 failed) |
| `nox -s integration_tests` | My 3 tests pass (13 pre-existing failures) |
| `nox -s coverage_report` | PASS (98%, threshold 97%) |
Closes#1100
Reviewed-on: cleveragents/cleveragents-core#1130
Reviewed-by: Jeffrey Phillips Freeman <jeffrey.freeman@cleverthis.com>
Co-authored-by: Brent E. Edwards <brent.edwards@cleverthis.com>
Co-committed-by: Brent E. Edwards <brent.edwards@cleverthis.com>