---
id: T02
parent: S02
milestone: M001
provides:
  - "Unknown key detection with 'did you mean?' fuzzy suggestions via difflib"
  - "CONFIG_TEMPLATE for policyfoundry init command"
  - "ConfigSource enum and AnnotatedValue dataclass for source provenance"
  - "resolve_with_annotations() for policyfoundry config show command"
  - "warn_unknown_keys() integrated into config loader"
requires: []
affects: []
key_files: []
key_decisions: []
patterns_established: []
observability_surfaces: []
drill_down_paths: []
duration: 4min
verification_result: passed
completed_at: 2026-03-08
blocker_discovered: false
---
# T02: 02-configuration-system 02

**# Phase 2 Plan 2: Unknown Key Detection, Config Template, and Source Annotations Summary**

## What Happened

# Phase 2 Plan 2: Unknown Key Detection, Config Template, and Source Annotations Summary

**Unknown key detection with difflib fuzzy suggestions, YAML config template for init, and source annotation utilities for config show**

## Performance

- **Duration:** 4 min
- **Started:** 2026-03-08T17:51:48Z
- **Completed:** 2026-03-08T17:56:05Z
- **Tasks:** 2 (1 TDD with 2 commits, 1 standard with 1 commit)
- **Files modified:** 5

## Accomplishments
- Unknown YAML config keys produce "did you mean?" warnings using difflib.get_close_matches with 0.6 cutoff
- Unknown keys do NOT block config loading -- valid config values are still applied
- CONFIG_TEMPLATE provides a fully commented YAML template for policyfoundry init command
- ConfigSource enum and resolve_with_annotations() enable source provenance for config show
- All 77 tests passing (29 config + 48 Phase 1), ruff clean, pyright clean

## Task Commits

Each task was committed atomically (TDD: test then feat):

1. **Task 1: Unknown key detection with TDD tests**
   - `355bc4d` (test) - add failing tests for unknown key detection
   - `8dcb053` (feat) - implement unknown key detection with fuzzy suggestions

2. **Task 2: Config template and source annotation utilities**
   - `f08f80a` (feat) - add config template and source annotation utilities

## Files Created/Modified
- `src/policyfoundry/config/validation.py` - KNOWN_KEYS registry, warn_unknown_keys() with difflib fuzzy matching
- `src/policyfoundry/config/defaults.py` - CONFIG_TEMPLATE, ConfigSource enum, AnnotatedValue dataclass, resolve_with_annotations()
- `src/policyfoundry/config/loader.py` - Integrated warn_unknown_keys() call before config loading
- `src/policyfoundry/config/__init__.py` - Added exports: warn_unknown_keys, CONFIG_TEMPLATE, ConfigSource, AnnotatedValue, resolve_with_annotations
- `tests/test_config/test_validation.py` - 7 tests for unknown key detection and error messages

## Decisions Made
- Used `cast()` for pyright strict compliance on `yaml.safe_load` and `model_dump` output types -- these return `Any` which pyright strict mode rejects for iteration
- Extracted `_build_warning` helper in validation.py to keep line lengths under 88 chars while maintaining readable warning messages
- `resolve_with_annotations` loads each source layer independently and compares against the final config to determine provenance -- this is custom logic since pydantic-settings doesn't natively expose which source provided each value

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

None.

## User Setup Required

None - no external service configuration required.

## Next Phase Readiness
- Full config system complete (models, loader, validation, template, source annotations)
- Phase 9 CLI integration can wire policyfoundry init (using CONFIG_TEMPLATE) and policyfoundry config show (using resolve_with_annotations)
- All downstream phases can import from policyfoundry.config for configuration access

## Self-Check: PASSED

- All 5 created/modified files exist on disk
- All 3 task commits verified (355bc4d, 8dcb053, f08f80a)
- 77 tests passing (29 config + 48 Phase 1)
- ruff: clean
- pyright: clean

---
*Phase: 02-configuration-system*
*Completed: 2026-03-08*
