---
id: T01
parent: S03
milestone: M001
provides: []
requires: []
affects: []
key_files: ["engine/presets/sign.json", "engine/presets/patch.json", "engine/presets/stencil.json", "engine/presets/detailed.json", "engine/presets/custom.json", "engine/presets/loader.py", "engine/api/routes.py", "engine/tests/test_presets.py"]
key_decisions: ["Preset default is 'sign' (was 'default' placeholder); mode defaults to None and comes from preset unless explicitly overridden", "Presets stored as flat JSON with three sections (preprocessing, vectorization, postprocessing)", "Custom preset has empty param sections so pipeline defaults apply unless user provides overrides", "resolve_params merges preset → user_params with user taking precedence"]
patterns_established: []
drill_down_paths: []
observability_surfaces: []
duration: ""
verification_result: "Ran full test suite: 196 tests pass with 0 failures. 27 preset-specific tests cover loader unit tests, param resolution logic, GET endpoint response shape, and integration tests proving each preset works and different presets produce different output from the same input image."
completed_at: 2026-03-26T04:45:48.689Z
blocker_discovered: false
---

# T01: Implemented 5 preset configs (sign, patch, stencil, detailed, custom), preset loader with param resolution, GET /engine/presets endpoint, and wired preset selection into /engine/trace pipeline

> Implemented 5 preset configs (sign, patch, stencil, detailed, custom), preset loader with param resolution, GET /engine/presets endpoint, and wired preset selection into /engine/trace pipeline

## What Happened
---
id: T01
parent: S03
milestone: M001
key_files:
  - engine/presets/sign.json
  - engine/presets/patch.json
  - engine/presets/stencil.json
  - engine/presets/detailed.json
  - engine/presets/custom.json
  - engine/presets/loader.py
  - engine/api/routes.py
  - engine/tests/test_presets.py
key_decisions:
  - Preset default is 'sign' (was 'default' placeholder); mode defaults to None and comes from preset unless explicitly overridden
  - Presets stored as flat JSON with three sections (preprocessing, vectorization, postprocessing)
  - Custom preset has empty param sections so pipeline defaults apply unless user provides overrides
  - resolve_params merges preset → user_params with user taking precedence
duration: ""
verification_result: passed
completed_at: 2026-03-26T04:45:48.702Z
blocker_discovered: false
---

# T01: Implemented 5 preset configs (sign, patch, stencil, detailed, custom), preset loader with param resolution, GET /engine/presets endpoint, and wired preset selection into /engine/trace pipeline

**Implemented 5 preset configs (sign, patch, stencil, detailed, custom), preset loader with param resolution, GET /engine/presets endpoint, and wired preset selection into /engine/trace pipeline**

## What Happened

Created engine/presets/ package with 5 JSON config files tuned for distinct use cases (sign=aggressive simplification, patch=smooth curves with auto-close, stencil=heavy simplification with fixed threshold, detailed=max fidelity, custom=empty defaults). Built loader.py with in-memory cache and resolve_params() that merges preset defaults with user overrides. Added GET /engine/presets endpoint. Rewired /engine/trace to resolve all pipeline params through the preset system — mode now comes from preset unless explicitly overridden, and postprocessing passes close_tolerance and auto_close from preset config. Updated existing test to validate unknown presets are rejected.

## Verification

Ran full test suite: 196 tests pass with 0 failures. 27 preset-specific tests cover loader unit tests, param resolution logic, GET endpoint response shape, and integration tests proving each preset works and different presets produce different output from the same input image.

## Verification Evidence

| # | Command | Exit Code | Verdict | Duration |
|---|---------|-----------|---------|----------|
| 1 | `cd engine && python -m pytest tests/ -v -k preset` | 0 | ✅ pass | 600ms |
| 2 | `cd engine && python -m pytest tests/ -v` | 0 | ✅ pass | 960ms |


## Deviations

Test for different preset outputs required a complex test image (circles, lines, speckle) instead of the simple rectangle fixture. Added auto_close and close_tolerance postprocessing params to preset-driven trace flow (already supported by postprocess_svg but not previously exposed through API).

## Known Issues

None.

## Files Created/Modified

- `engine/presets/sign.json`
- `engine/presets/patch.json`
- `engine/presets/stencil.json`
- `engine/presets/detailed.json`
- `engine/presets/custom.json`
- `engine/presets/loader.py`
- `engine/api/routes.py`
- `engine/tests/test_presets.py`


## Deviations
Test for different preset outputs required a complex test image (circles, lines, speckle) instead of the simple rectangle fixture. Added auto_close and close_tolerance postprocessing params to preset-driven trace flow (already supported by postprocess_svg but not previously exposed through API).

## Known Issues
None.
