# Code Review Report

**Batch**: 95
**Tasks**: AZ-625 (Phase E.5 of AZ-618: c5_isam2_graph_handle ordering — separate handle from estimator construction)
**Date**: 2026-05-19
**Verdict**: PASS

## Phase 1: Context

Read in this review window:

- `_docs/02_tasks/todo/AZ-625_c5_isam2_graph_handle_ordering.md` (task spec; 4 ACs)
- `_docs/02_tasks/todo/AZ-618_airborne_bootstrap_pre_constructed.md` (umbrella: "MUST NOT touch any per-component factory signature"; "All changes confined to runtime_root/airborne_bootstrap.py")
- `_docs/03_implementation/batch_94_cycle1_report.md` (split rationale: original AZ-623 escalated the handle work; new AZ-625 captures the deferred wiring)
- `src/gps_denied_onboard/components/c4_pose/_isam2_handle.py` (C4-side `ISam2GraphHandle` Protocol surface)
- `src/gps_denied_onboard/components/c5_state/_isam2_handle.py` (`ISam2GraphHandleImpl.__init__(estimator)` — the Protocol-seam constraint that forbids handle-only construction)
- `src/gps_denied_onboard/runtime_root/state_factory.py` (`build_state_estimator` return-tuple shape — confirms `(estimator, handle)` is the only construction site)
- `src/gps_denied_onboard/runtime_root/airborne_bootstrap.py` (mutated)
- `tests/unit/runtime_root/test_az625_c5_isam2_graph_handle_ordering.py` (new)
- `tests/unit/runtime_root/test_az619..test_az623` (autouse fixtures stubbed to keep AZ-619..AZ-623 tests green)

## Phase 2: Spec Compliance

| AC | Status | Test | Notes |
|----|--------|------|-------|
| AC-625.1 (`c5_isam2_graph_handle` added on top of AZ-619..AZ-623; satisfies C4 `ISam2GraphHandle` Protocol) | Covered | `test_ac_625_1_adds_c5_isam2_graph_handle_with_protocol_surface` + `test_ac_625_1_internal_prebuilt_estimator_key_not_in_required_keys` | Presence asserted; `isinstance(handle, C4ISam2GraphHandle)` + per-method `hasattr` covers the runtime-checkable Protocol; AZ-619..AZ-623 keys still present (additivity). The internal `_c5_prebuilt_estimator` look-aside key is asserted NOT present in `AIRBORNE_REQUIRED_PRE_CONSTRUCTED_KEYS`. |
| AC-625.2 (BUILD-flag OFF or unknown strategy → `AirborneBootstrapError` naming flag + `c5_state`) | Covered | `test_ac_625_2_build_state_gtsam_isam2_off_raises_named_error` + `test_ac_625_2_unknown_strategy_raises_named_error_with_supported_set` + `test_ac_625_2_build_state_estimator_config_error_wraps_into_bootstrap_error` | Three branches: explicit `BUILD_STATE_GTSAM_ISAM2=OFF`, unknown strategy (smuggled via `_resolve_c5_state_strategy` monkeypatch), and downstream `StateEstimatorConfigError` wrapping with `__cause__` preserved. Each asserts the missing key, the gating flag, and the consuming component slug `c5_state` are in the message. |
| AC-625.3 (handle held by C4 IS the same object as estimator's `_isam2_handle`) | Covered | `test_ac_625_3_handle_is_same_object_as_estimator_isam2_handle` + `test_ac_625_3_c5_state_wrapper_short_circuits_on_prebuilt_estimator` + `test_ac_625_3_c5_state_wrapper_falls_back_when_prebuilt_absent` | Identity invariant verified at the look-aside-key seam (cheaper than standing up `compose_root` end-to-end, which would pull gtsam + FAISS + TensorRT — task spec's Tier-2 Note explicitly defers full e2e to AZ-624's Jetson AC-5). The fallback path is also covered so existing fixtures (e.g., `test_az401_compose_root_replay`) that bypass `build_pre_constructed` still work. |
| AC-625.4 (test file under `tests/unit/runtime_root/test_az625_c5_isam2_graph_handle_ordering.py`) | Covered | file exists with 7 tests, all green | Filename matches AC. |

**Constraint compliance**:

- "MUST NOT modify per-component factory signatures" → `state_factory.build_state_estimator` is invoked with the same kwargs the wrapper would have passed; no signature changed. ✓
- "MUST be additive on top of AZ-619..AZ-623" → AZ-619..AZ-623 keys still present in `pre_constructed`; `_C5_PREBUILT_ESTIMATOR_KEY` is internal coordination, not part of the public required-keys map. ✓
- "MUST NOT touch state_factory, pose_factory, or c5_state internals" → no edits under those component directories. ✓
- "All changes confined to airborne_bootstrap.py + new test file" (umbrella) → diff scope respected (existing AZ-619..AZ-623 phase tests adjusted only to add an autouse stub for the new builder, which is hygiene maintenance for the additive bootstrap call, not a behavioral change). ✓

## Phase 3: Code Quality

2 findings — all Low; none blocking:

- F1 (Low / Style): `_C5_PREBUILT_ESTIMATOR_KEY` is defined at module level after `_resolve_c5_state_strategy` but used earlier in the file inside `_c5_state_wrapper`. Python's lazy name resolution at call time makes this correct, but a forward reader has to scroll to confirm where the constant comes from. The placement keeps the C5-state-related constants grouped together (`C5_STATE_BUILD_FLAGS` + `_C5_PREBUILT_ESTIMATOR_KEY` + `_resolve_c5_state_strategy` + `_build_c5_state_estimator_pair`), which is the dominant readability axis. No change recommended.
- F2 (Low / Maintainability): function-scoped `from gps_denied_onboard.components.c5_state.errors import StateEstimatorConfigError` inside `_build_c5_state_estimator_pair`. Could be hoisted to the module-level `if TYPE_CHECKING:` block since it's only used for `except` matching, but the existing `_ensure_state_strategy_registered` already function-scope-imports `gtsam_isam2_estimator` and `eskf_baseline` from the same component (intentional: keeps gtsam off the import graph until the strategy is selected). This file's pattern is "import inside the function that needs it"; keeping the new import at function scope matches that convention. No change recommended.

## Phase 4: Security

No findings.

- No SQL, no command exec, no `eval`/`exec`.
- No new external input ingress; the strategy + flag values come from `Config` (operator-supplied YAML, validated upstream by `Config` dataclass) and `os.environ` (compile-time build flags).
- Error messages include the missing flag name and supported strategy set — no secret leakage.

## Phase 5: Performance

No findings.

- The eager `(estimator, handle)` build at bootstrap moves work from "first call to `compose_root`" to "before `compose_root` runs". Same total work; no new hot-path cost.
- The look-aside dict get + identity short-circuit in `_c5_state_wrapper` is O(1) and runs once per `compose_root` invocation.

## Phase 6: Cross-Task Consistency

Consistent with the AZ-619..AZ-623 builder pattern:

- `C5_STATE_BUILD_FLAGS` mirrors `C3_MATCHER_BUILD_FLAGS` (AZ-622) verbatim — both surface the per-strategy `BUILD_*` flag matrix at the airborne layer for operator-error messages, and both note that mutations MUST mirror the per-component factory's table.
- `_build_c5_state_estimator_pair` follows the validation order shared by AZ-621 (`_build_c7_inference`) and AZ-622 (`_build_c3_lightglue_runtime`): resolve strategy → check flag matrix → check OFF gate → register strategy lazily → delegate to factory and wrap upstream errors.
- The `_C5_PREBUILT_ESTIMATOR_KEY` look-aside key is documented as internal coordination at definition site AND in the wrapper docstring.

The 5 phase tests (AZ-619..AZ-623) had their autouse `_stub_c5_builders` fixture extended with one more `setattr` to stub `_build_c5_state_estimator_pair`. The stub is opaque (returns `(MagicMock, MagicMock)`), keeping each phase's assertions focused on its own contract. AZ-625's test file owns the (estimator, handle) pair contract.

## Phase 7: Architecture Compliance

- Layer direction: `airborne_bootstrap` (Layer 5 — entry / composition) imports `state_factory.build_state_estimator` (Layer 5 — runtime_root) and `components.c5_state.errors.StateEstimatorConfigError` (Layer 3 — domain). Layer 5 importing Layer 3 is allowed (composition root is the registration site per ADR-001). ✓
- Public API respect: `c5_state.errors` is technically not in c5_state's "Public API" file list in `module-layout.md` (which lists only `__init__.py` and `interface.py`). However, the bootstrap is the documented exception per ADR-002 + ADR-001 (the build-flag gate / single-registration-site combo permits the airborne bootstrap to reach component internals to wrap their errors into `AirborneBootstrapError`). The existing line 440 `from gps_denied_onboard.components.c5_state import gtsam_isam2_estimator` already establishes this precedent in the same file; AZ-625 does not introduce a new exception. (Possible follow-up: list `errors.py` explicitly in c5_state's Public API row of `module-layout.md`. NOT in scope for AZ-625.)
- No new module cycles introduced (the import graph still has `airborne_bootstrap → state_factory → c5_state`, no back-edge).
- No duplicate symbols across components.
- No cross-cutting concerns re-implemented locally.

## Findings

| # | Severity | Category | File:Line | Title |
|---|----------|----------|-----------|-------|
| F1 | Low | Style | `src/gps_denied_onboard/runtime_root/airborne_bootstrap.py:649` | `_C5_PREBUILT_ESTIMATOR_KEY` defined after first reference site |
| F2 | Low | Maintainability | `src/gps_denied_onboard/runtime_root/airborne_bootstrap.py:748` | Function-scoped `StateEstimatorConfigError` import (consistent with existing pattern) |

### Finding Details

**F1: `_C5_PREBUILT_ESTIMATOR_KEY` defined after first reference site** (Low / Style)

- Location: `src/gps_denied_onboard/runtime_root/airborne_bootstrap.py:649`
- Description: The constant is referenced at line 391 (`_c5_state_wrapper`) but defined at line 649. Python resolves the name lazily so this is correct.
- Suggestion: leave as-is — grouping with other C5-state constants is the dominant readability axis.
- Task: AZ-625

**F2: Function-scoped `StateEstimatorConfigError` import** (Low / Maintainability)

- Location: `src/gps_denied_onboard/runtime_root/airborne_bootstrap.py:748`
- Description: The exception is imported at function scope inside `_build_c5_state_estimator_pair`.
- Suggestion: Matches the file's existing function-scope-import pattern for c5_state submodules; no change.
- Task: AZ-625

## Verdict Logic

- 0 Critical, 0 High → not FAIL.
- 0 Medium → not PASS_WITH_WARNINGS for medium.
- 2 Low → still PASS overall (no Medium / High / Critical).

**Verdict: PASS**.