---
id: T01
parent: S01
milestone: M010
provides: []
requires: []
affects: []
key_files: ["backend/routers/topics.py", "backend/tests/test_public_api.py"]
key_decisions: ["Used PostgreSQL ARRAY contains (@>) for tag matching — simpler than unnest/ANY since tags are stored lowercase", "Route registered before /{category_slug} to prevent FastAPI path conflict"]
patterns_established: []
drill_down_paths: []
observability_surfaces: []
duration: ""
verification_result: "Ran pytest with -k subtopic filter against real PostgreSQL test database. All 3 new tests pass: test_get_subtopic_techniques, test_get_subtopic_techniques_empty, test_get_subtopic_techniques_pagination."
completed_at: 2026-03-31T05:59:22.035Z
blocker_discovered: false
---

# T01: Added GET /topics/{category_slug}/{subtopic_slug} endpoint filtering techniques by tag within a category, with 3 passing integration tests

> Added GET /topics/{category_slug}/{subtopic_slug} endpoint filtering techniques by tag within a category, with 3 passing integration tests

## What Happened
---
id: T01
parent: S01
milestone: M010
key_files:
  - backend/routers/topics.py
  - backend/tests/test_public_api.py
key_decisions:
  - Used PostgreSQL ARRAY contains (@>) for tag matching — simpler than unnest/ANY since tags are stored lowercase
  - Route registered before /{category_slug} to prevent FastAPI path conflict
duration: ""
verification_result: passed
completed_at: 2026-03-31T05:59:22.036Z
blocker_discovered: false
---

# T01: Added GET /topics/{category_slug}/{subtopic_slug} endpoint filtering techniques by tag within a category, with 3 passing integration tests

**Added GET /topics/{category_slug}/{subtopic_slug} endpoint filtering techniques by tag within a category, with 3 passing integration tests**

## What Happened

Added get_subtopic_techniques endpoint to routers/topics.py using PostgreSQL ARRAY contains (@>) for tag matching. Route registered before /{category_slug} to avoid FastAPI path conflicts. Added 3 integration tests covering happy path, empty results, and pagination. Fixed pre-existing ProcessingStatus.extracted enum reference in test seed helper.

## Verification

Ran pytest with -k subtopic filter against real PostgreSQL test database. All 3 new tests pass: test_get_subtopic_techniques, test_get_subtopic_techniques_empty, test_get_subtopic_techniques_pagination.

## Verification Evidence

| # | Command | Exit Code | Verdict | Duration |
|---|---------|-----------|---------|----------|
| 1 | `python -m pytest tests/test_public_api.py -k subtopic -v` | 0 | ✅ pass | 1600ms |


## Deviations

Fixed pre-existing ProcessingStatus.extracted → ProcessingStatus.complete in test seed helper. Used ARRAY contains instead of unnest/ANY approach.

## Known Issues

Pre-existing: test_list_topics_hierarchy and test_topics_with_no_technique_pages hardcode len(data) == 6 but canonical_tags.yaml now has 7 categories.

## Files Created/Modified

- `backend/routers/topics.py`
- `backend/tests/test_public_api.py`


## Deviations
Fixed pre-existing ProcessingStatus.extracted → ProcessingStatus.complete in test seed helper. Used ARRAY contains instead of unnest/ANY approach.

## Known Issues
Pre-existing: test_list_topics_hierarchy and test_topics_with_no_technique_pages hardcode len(data) == 6 but canonical_tags.yaml now has 7 categories.
