---
phase: 13-registry-mode-enum
plan: 02
subsystem: api
tags: [ouroboros, aion, type-stubs, literal-types, python-api]

requires:
  - phase: 13-01
    provides: OuroborosMode enum with DAY and AION variants, validate_ouroboros_mode()
provides:
  - All public API signatures accept ouroboros_mode="aion" alongside "day"
  - Type stubs (.pyi) updated for IDE/AI type checking
affects: [14-rust-aion-processor, sidecar, kintsugi]

tech-stack:
  added: []
  patterns: [Literal union types for mode parameters]

key-files:
  created: []
  modified:
    - python/opendeviationbar/orchestration/open_deviation_bars.py
    - python/opendeviationbar/orchestration/open_deviation_bars.pyi
    - python/opendeviationbar/checkpoint/__init__.py
    - python/opendeviationbar/checkpoint/__init__.pyi

key-decisions:
  - "No runtime changes needed -- validate_ouroboros_mode() from Plan 01 already handles acceptance"

patterns-established:
  - "Literal['day', 'aion'] union for all ouroboros_mode parameters"

requirements-completed: [REG-04]

duration: 1min
completed: 2026-03-27
---

# Phase 13 Plan 02: API Signature Expansion Summary

**Expanded all public Python API ouroboros_mode parameters from Literal["day"] to Literal["day", "aion"] with matching type stubs**

## Performance

- **Duration:** 1 min
- **Started:** 2026-03-27T05:24:42Z
- **Completed:** 2026-03-27T05:25:42Z
- **Tasks:** 1
- **Files modified:** 4

## Accomplishments

- Updated get_open_deviation_bars() signature and docstring to accept "aion"
- Updated all 3 overloads in open_deviation_bars.pyi (2 @overload + 1 impl)
- Updated populate_cache_resumable and populate_cache_multi_threshold type stubs
- Updated checkpoint docstring to reflect both modes supported

## Task Commits

Each task was committed atomically:

1. **Task 1: Expand Literal["day"] to Literal["day", "aion"] in all API signatures and stubs** - `33a9ad1` (feat)

**Plan metadata:** (pending)

## Files Created/Modified

- `python/opendeviationbar/orchestration/open_deviation_bars.py` - Updated ouroboros_mode type annotation and docstring
- `python/opendeviationbar/orchestration/open_deviation_bars.pyi` - Updated all 3 overload signatures
- `python/opendeviationbar/checkpoint/__init__.py` - Updated docstring for ouroboros_mode
- `python/opendeviationbar/checkpoint/__init__.pyi` - Updated both function stubs

## Decisions Made

- No runtime changes needed: validate_ouroboros_mode() from Plan 01 already handles "aion" acceptance at runtime
- count_bounded.py and precompute.py use `str | None` (not Literal) so no type annotation changes needed there

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

None

## User Setup Required

None - no external service configuration required.

## Next Phase Readiness

- All public API surfaces accept ouroboros_mode="aion"
- Ready for Rust processor implementation of Aion mode in subsequent phases
- Type stubs ensure IDE autocomplete and type checker support

---

_Phase: 13-registry-mode-enum_
_Completed: 2026-03-27_

## Self-Check: PASSED
