---
phase: 04-retrieval-nodes
plan: "03"
subsystem: retrieval
tags: [rrf, score-fusion, context-assembly, token-budgeting, hybrid-search]
# Dependency graph
requires:
- phase: 04-retrieval-nodes
provides: [RankedComponent model, GraphStore protocol, PPR scores]
provides:
- RRF score fusion for vector+graph hybrid results
- Token-budgeted context assembler with type priority
- Post-fusion type filtering (not during retrieval)
affects: [05-orchestration, phase-4-complete, retrieval-pipeline]
# Tech tracking
tech-stack:
added: []
patterns:
- "RRF k=60 for hybrid score fusion"
- "Type filter AFTER fusion, not during retrieval"
- "Type priority ordering: agents > skills > commands"
- "4 chars/token conservative token estimation"
key-files:
created:
- src/skill_retriever/nodes/retrieval/score_fusion.py
- src/skill_retriever/nodes/retrieval/context_assembler.py
- tests/test_score_fusion.py
- tests/test_context_assembler.py
modified:
- src/skill_retriever/nodes/retrieval/__init__.py
key-decisions:
- "RRF k=60: Empirically validated default from Elasticsearch/Milvus research"
- "Type filter post-fusion: Applying during retrieval causes semantic mismatch per research"
- "TYPE_PRIORITY dict: agents(1) > skills(2) > commands(3) for context assembly ordering"
- "Ternary for type_priority: SIM108 compliance with pyright type narrowing"
patterns-established:
- "Post-fusion filtering: Always filter AFTER score fusion to preserve semantic ranking"
- "Token budgeting: Conservative 4 chars/token estimation for LLM context windows"
- "RetrievalContext dataclass: Standard return type for context assembly with truncation tracking"
# Metrics
duration: 8min
completed: 2026-02-03
---
# Phase 4 Plan 03: Score Fusion & Context Assembly Summary
**RRF hybrid score fusion with k=60 and token-budgeted context assembler using type priority ordering**
## Performance
- **Duration:** 8 min
- **Started:** 2026-02-03T06:57:23Z
- **Completed:** 2026-02-03T07:05:XX Z
- **Tasks:** 2
- **Files modified:** 5
## Accomplishments
- Reciprocal Rank Fusion implementation combining vector and graph results
- Post-fusion type filtering preserving semantic ranking
- Token-budgeted context assembly with type priority (agents before skills before commands)
- RetrievalContext dataclass tracking truncation state and excluded count
## Task Commits
Each task was committed atomically:
1. **Task 1: Create RRF score fusion** - `1524ade` (feat)
2. **Task 2: Create context assembler with token budgeting** - `4e4679f` (feat)
## Files Created/Modified
- `src/skill_retriever/nodes/retrieval/score_fusion.py` - RRF implementation with fuse_retrieval_results
- `src/skill_retriever/nodes/retrieval/context_assembler.py` - Token budgeting with type priority
- `tests/test_score_fusion.py` - 8 tests covering RRF and fusion
- `tests/test_context_assembler.py` - 7 tests covering token budgeting and priority
- `src/skill_retriever/nodes/retrieval/__init__.py` - Added 4 new exports
## Decisions Made
1. **RRF k=60 constant** - Standard default from Elasticsearch/Milvus empirical research. Higher k values reduce score gap between adjacent ranks, providing smoother fusion.
2. **Type filter post-fusion** - Research pitfall #3: filtering during retrieval causes semantic mismatch. Filter AFTER fusion preserves the semantic ranking quality from both vector and graph sources.
3. **TYPE_PRIORITY ordering** - Agents (1) > Skills (2) > Commands (3) > MCP (4) > Hooks (5) > Settings (6) > Sandbox (7). Reflects Claude Code component importance hierarchy.
4. **Ternary operator for type_priority** - SIM108 compliance. Pyright type narrowing works correctly with ternary form for node None check.
## Deviations from Plan
### Auto-fixed Issues
**1. [Rule 3 - Blocking] Fixed ruff SIM108 and RUF022 lint errors**
- **Found during:** Task 2 verification
- **Issue:** Ruff flagged if/else block (SIM108) and unsorted `__all__` (RUF022)
- **Fix:** Used ternary operator for type_priority; ran `ruff --fix` to sort `__all__`
- **Files modified:** context_assembler.py, __init__.py
- **Verification:** `ruff check` passes
- **Committed in:** 4e4679f (Task 2 commit)
**2. [Rule 3 - Blocking] Fixed pyright unnecessary comparison error**
- **Found during:** Task 2 verification
- **Issue:** `node.component_type is None` check flagged as always False (ComponentType is StrEnum, never None)
- **Fix:** Removed redundant None check for component_type, kept only node None check
- **Files modified:** context_assembler.py
- **Verification:** `pyright` passes with 0 errors
- **Committed in:** 4e4679f (Task 2 commit)
---
**Total deviations:** 2 auto-fixed (2 blocking)
**Impact on plan:** Both auto-fixes necessary for lint/type compliance. No scope creep.
## Issues Encountered
None - plan executed smoothly after lint fixes.
## User Setup Required
None - no external service configuration required.
## Next Phase Readiness
- Phase 4 retrieval nodes complete (all 3 plans done)
- Full retrieval pipeline ready: query planner, vector search, PPR engine, flow pruner, score fusion, context assembler
- Ready for Phase 5: Orchestration (LangGraph workflow integration)
- All 124 tests pass, pyright clean on source code
---
*Phase: 04-retrieval-nodes*
*Completed: 2026-02-03*
