[AZ-623] [AZ-625] Phase E: c282_ransac + c5 helpers; split handle work

Wire 4 stateless / cached helpers into airborne_bootstrap.build_pre_constructed:
c282_ransac_filter, c5_imu_preintegrator (cached on calibration path),
c5_se3_utils (helpers.se3_utils module as namespace handle), c5_wgs_converter.

The original AZ-623 5th deliverable (c5_isam2_graph_handle) hit an
unresolvable construction-order conflict between c4_pose (consumes the handle)
and c5_state (creates it inside build_state_estimator's tuple return) under
the umbrella's "MUST NOT touch any per-component factory signature" constraint.
Per AZ-623 spec's escalation gate, scope was split: AZ-625 captures the handle
ordering work; AZ-624 dependency edge updated to require both.

Tests: tests/unit/runtime_root/test_az623_pre_constructed_phase_e.py adds 7
tests covering AC-623.1..3 (4 new keys + correct types, IMU preintegrator
caching, operator-actionable error messages for empty / unreadable / malformed
calibration paths). Autouse stubs added to test_az619/620/621/622 so prior
phase tests remain isolated from new builders.

Quality gates: ruff format clean, ruff lint clean, 24/24 phase tests pass,
247/247 runtime_root + c5_state regression suite passes. Code review verdict
PASS_WITH_WARNINGS (3 Low findings; full report in
_docs/03_implementation/reviews/batch_94_review.md).

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/unit/runtime_root/test_az619_pre_constructed_phase_a.py

@@ -59,12 +59,8 @@ def _stub_c6_builders(monkeypatch: pytest.MonkeyPatch) -> None:
     # Config() used below would hit KeyError inside storage_factory's
     # config.components["c6_tile_cache"] lookup. Sentinel objects are
     # opaque on purpose — the AZ-619 assertions never inspect them.
-    monkeypatch.setattr(
-        airborne_bootstrap, "_build_c6_descriptor_index", lambda _config: object()
-    )
-    monkeypatch.setattr(
-        airborne_bootstrap, "_build_c6_tile_store", lambda _config: object()
-    )
+    monkeypatch.setattr(airborne_bootstrap, "_build_c6_descriptor_index", lambda _config: object())
+    monkeypatch.setattr(airborne_bootstrap, "_build_c6_tile_store", lambda _config: object())
 
 
 @pytest.fixture(autouse=True)
@@ -75,9 +71,7 @@ def _stub_c7_inference_builder(monkeypatch: pytest.MonkeyPatch) -> None:
     # config.components["c7_inference"] lookup, AND the airborne BUILD_*
     # flags are typically unset in the test env. The sentinel is opaque
     # on purpose — AZ-619 assertions never inspect it.
-    monkeypatch.setattr(
-        airborne_bootstrap, "_build_c7_inference", lambda _config: object()
-    )
+    monkeypatch.setattr(airborne_bootstrap, "_build_c7_inference", lambda _config: object())
 
 
 @pytest.fixture(autouse=True)
@@ -93,9 +87,22 @@ def _stub_c3_matcher_builders(monkeypatch: pytest.MonkeyPatch) -> None:
         "_build_c3_lightglue_runtime",
         lambda _config, *, inference_runtime: object(),
     )
-    monkeypatch.setattr(
-        airborne_bootstrap, "_build_c3_feature_extractor", lambda _config: object()
-    )
+    monkeypatch.setattr(airborne_bootstrap, "_build_c3_feature_extractor", lambda _config: object())
+
+
+@pytest.fixture(autouse=True)
+def _stub_c5_builders(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange: stub the AZ-623 Phase E c5 / RANSAC builders so the AZ-619
+    # tests stay focused on Phase A. Without this the bare Config() below
+    # would hit _build_c5_imu_preintegrator's
+    # config.runtime.camera_calibration_path empty-check and raise
+    # AirborneBootstrapError before the AC-619 keys could be asserted.
+    # Sentinels are opaque on purpose — AZ-619 assertions never inspect
+    # them.
+    monkeypatch.setattr(airborne_bootstrap, "_build_c282_ransac_filter", lambda _config: object())
+    monkeypatch.setattr(airborne_bootstrap, "_build_c5_imu_preintegrator", lambda _config: object())
+    monkeypatch.setattr(airborne_bootstrap, "_build_c5_se3_utils", lambda _config: object())
+    monkeypatch.setattr(airborne_bootstrap, "_build_c5_wgs_converter", lambda _config: object())
 
 
 def test_ac_619_1_default_config_seeds_c13_fdr_and_clock() -> None:

tests/unit/runtime_root/test_az620_pre_constructed_phase_b.py

@@ -95,6 +95,37 @@ def _stub_c3_matcher_builders(monkeypatch: pytest.MonkeyPatch) -> None:
     )
 
 
+@pytest.fixture(autouse=True)
+def _stub_c5_builders(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange: stub the AZ-623 Phase E c5 / RANSAC builders so AZ-620
+    # tests stay focused on the Phase B contract. Without this the configs
+    # used below would hit _build_c5_imu_preintegrator's
+    # config.runtime.camera_calibration_path empty-check and raise
+    # AirborneBootstrapError before the AC-620 keys could be asserted.
+    # MagicMock sentinels are opaque on purpose — AZ-620 assertions
+    # never inspect them.
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c282_ransac_filter",
+        lambda _config: MagicMock(name="RansacFilter"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_imu_preintegrator",
+        lambda _config: MagicMock(name="ImuPreintegrator"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_se3_utils",
+        lambda _config: MagicMock(name="Se3Utils"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_wgs_converter",
+        lambda _config: MagicMock(name="WgsConverter"),
+    )
+
+
 def test_ac_620_1_adds_c6_descriptor_index_and_c6_tile_store(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:

tests/unit/runtime_root/test_az621_pre_constructed_phase_c.py

@@ -98,6 +98,37 @@ def _stub_c3_matcher_builders(monkeypatch: pytest.MonkeyPatch) -> None:
     )
 
 
+@pytest.fixture(autouse=True)
+def _stub_c5_builders(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange: stub the AZ-623 Phase E c5 / RANSAC builders so AZ-621
+    # tests stay focused on the Phase C contract. Without this the configs
+    # used below would hit _build_c5_imu_preintegrator's
+    # config.runtime.camera_calibration_path empty-check and raise
+    # AirborneBootstrapError before the AC-621 keys could be asserted.
+    # Sentinels are opaque on purpose — AZ-621 assertions never inspect
+    # them.
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c282_ransac_filter",
+        lambda _config: MagicMock(name="RansacFilter"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_imu_preintegrator",
+        lambda _config: MagicMock(name="ImuPreintegrator"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_se3_utils",
+        lambda _config: MagicMock(name="Se3Utils"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_wgs_converter",
+        lambda _config: MagicMock(name="WgsConverter"),
+    )
+
+
 def test_ac_621_1_adds_c7_inference(monkeypatch: pytest.MonkeyPatch) -> None:
     # Arrange: stub build_inference_runtime to a sentinel so we can
     # assert wiring without standing up real GPU/TensorRT/PyTorch.
@@ -133,9 +164,7 @@ def test_ac_621_2_both_build_flags_off_with_configured_consumer_raises_named_err
         "build_inference_runtime",
         _raise_no_c7_runtime_available,
     )
-    config = Config.with_blocks(
-        c3_matcher=_C3MatcherBlock(strategy="disk_lightglue")
-    )
+    config = Config.with_blocks(c3_matcher=_C3MatcherBlock(strategy="disk_lightglue"))
 
     # Act + Assert
     with pytest.raises(AirborneBootstrapError) as excinfo:

tests/unit/runtime_root/test_az622_pre_constructed_phase_d.py

@@ -104,6 +104,35 @@ def _stub_c6_and_c7_builders(monkeypatch: pytest.MonkeyPatch) -> None:
     )
 
 
+@pytest.fixture(autouse=True)
+def _stub_c5_builders(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange: stub the AZ-623 Phase E c5 / RANSAC builders so AZ-622
+    # tests stay focused on the Phase D contract. Without this the configs
+    # used below would hit _build_c5_imu_preintegrator's
+    # config.runtime.camera_calibration_path empty-check and raise
+    # AirborneBootstrapError before the AC-622 keys could be asserted.
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c282_ransac_filter",
+        lambda _config: MagicMock(name="RansacFilter"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_imu_preintegrator",
+        lambda _config: MagicMock(name="ImuPreintegrator"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_se3_utils",
+        lambda _config: MagicMock(name="Se3Utils"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c5_wgs_converter",
+        lambda _config: MagicMock(name="WgsConverter"),
+    )
+
+
 def test_ac_622_1_adds_c3_lightglue_runtime_and_c3_feature_extractor(
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
@@ -130,10 +159,7 @@ def test_ac_622_1_adds_c3_lightglue_runtime_and_c3_feature_extractor(
     assert "c3_lightglue_runtime" in pre_constructed
     assert "c3_feature_extractor" in pre_constructed
     assert isinstance(pre_constructed["c3_lightglue_runtime"], LightGlueRuntime)
-    assert (
-        pre_constructed["c3_lightglue_runtime"].descriptor_dim()
-        == engine_handle.descriptor_dim
-    )
+    assert pre_constructed["c3_lightglue_runtime"].descriptor_dim() == engine_handle.descriptor_dim
     assert isinstance(pre_constructed["c3_feature_extractor"], FeatureExtractor)
     assert isinstance(pre_constructed["c3_feature_extractor"], OpenCvOrbExtractor)
     assert {
@@ -154,9 +180,7 @@ def test_ac_622_2_build_flag_off_with_configured_strategy_raises_named_error(
     # fire BEFORE _load_lightglue_engine_handle is consulted, so we don't
     # need to stub the loader for this branch.
     monkeypatch.delenv("BUILD_MATCHER_DISK_LIGHTGLUE", raising=False)
-    config = Config.with_blocks(
-        c3_matcher=_C3MatcherBlock(strategy="disk_lightglue")
-    )
+    config = Config.with_blocks(c3_matcher=_C3MatcherBlock(strategy="disk_lightglue"))
 
     # Act + Assert
     with pytest.raises(AirborneBootstrapError) as excinfo:
@@ -168,9 +192,7 @@ def test_ac_622_2_build_flag_off_with_configured_strategy_raises_named_error(
     # AC-622.2 + AZ-618 NFR "operator-facing error contract").
     assert "c3_lightglue_runtime" in message
     expected_flag = C3_MATCHER_BUILD_FLAGS["disk_lightglue"]
-    assert expected_flag in message, (
-        f"{expected_flag!r} missing from error: {message!r}"
-    )
+    assert expected_flag in message, f"{expected_flag!r} missing from error: {message!r}"
     assert "c3_matcher" in message
     # The flag-OFF branch raises directly — there is no upstream cause to
     # preserve (cause-chain preservation is exercised in
@@ -184,9 +206,7 @@ def test_ac_622_2_build_flag_off_with_aliked_strategy_names_aliked_flag(
     """Per-strategy flag specificity: aliked_lightglue surfaces ALIKED's flag."""
     # Arrange: ALIKED strategy with its own gating flag OFF.
     monkeypatch.delenv("BUILD_MATCHER_ALIKED_LIGHTGLUE", raising=False)
-    config = Config.with_blocks(
-        c3_matcher=_C3MatcherBlock(strategy="aliked_lightglue")
-    )
+    config = Config.with_blocks(c3_matcher=_C3MatcherBlock(strategy="aliked_lightglue"))
 
     # Act + Assert
     with pytest.raises(AirborneBootstrapError) as excinfo:
@@ -245,9 +265,7 @@ def test_ac_622_2_lightglue_engine_load_failure_wraps_runtime_error(
         "_load_lightglue_engine_handle",
         _raise_engine_load_failure,
     )
-    config = Config.with_blocks(
-        c3_matcher=_C3MatcherBlock(strategy="disk_lightglue")
-    )
+    config = Config.with_blocks(c3_matcher=_C3MatcherBlock(strategy="disk_lightglue"))
 
     # Act + Assert
     with pytest.raises(AirborneBootstrapError) as excinfo:
@@ -281,9 +299,7 @@ def test_lightglue_runtime_uses_c7_inference_from_pre_constructed(
         captured["inference_runtime"] = inference_runtime
         return _make_engine_handle_mock(descriptor_dim=128)
 
-    monkeypatch.setattr(
-        airborne_bootstrap, "_load_lightglue_engine_handle", _capture_loader
-    )
+    monkeypatch.setattr(airborne_bootstrap, "_load_lightglue_engine_handle", _capture_loader)
     config = Config()
 
     # Act

tests/unit/runtime_root/test_az623_pre_constructed_phase_e.py

@@ -0,0 +1,301 @@
+"""AZ-623 — Phase E of AZ-618: ``build_pre_constructed`` seeds c282_ransac_filter + 3 c5 helpers.
+
+Verifies the contract at
+``_docs/02_tasks/todo/AZ-623_pre_constructed_phase_e_ransac_c5_helpers.md``
+(scope-narrowed 2026-05-19; ``c5_isam2_graph_handle`` deferred to AZ-625):
+
+* AC-623.1: ``build_pre_constructed(default_config)`` adds
+  ``c282_ransac_filter`` (a :class:`RansacFilter` instance),
+  ``c5_imu_preintegrator`` (an :class:`ImuPreintegrator` instance),
+  ``c5_se3_utils`` (the :mod:`gps_denied_onboard.helpers.se3_utils`
+  module), and ``c5_wgs_converter`` (a :class:`WgsConverter` instance)
+  on top of AZ-619..AZ-622.
+* AC-623.2: invoking twice in the same process produces dicts where
+  ``c5_imu_preintegrator`` is the SAME instance both calls (cached by
+  ``config.runtime.camera_calibration_path``); the 3 stateless helpers
+  may be either fresh or cached.
+* AC-623.3: when ``config.runtime.camera_calibration_path`` is empty or
+  unreadable, ``_build_c5_imu_preintegrator`` raises
+  :class:`AirborneBootstrapError` whose message names the missing input
+  AND the consuming component slug ``c5_state``.
+
+AC-623.4 (this file exists with the above tests) is satisfied by the
+existence of this module.
+
+The tests stub the heavy ``_load_camera_calibration`` seam so they
+exercise the helper-wiring contract without standing up an on-disk
+calibration JSON. The upstream AZ-619..AZ-622 builders are stubbed at
+the airborne_bootstrap module boundary, mirroring the prior phase
+pattern (see :mod:`tests.unit.runtime_root.test_az622_pre_constructed_phase_d`).
+"""
+
+from __future__ import annotations
+
+import dataclasses
+from collections.abc import Iterator
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import numpy as np
+import pytest
+
+from gps_denied_onboard._types.calibration import CameraCalibration
+from gps_denied_onboard.config import Config
+from gps_denied_onboard.fdr_client import client as fdr_client_module
+from gps_denied_onboard.helpers import se3_utils as se3_utils_module
+from gps_denied_onboard.helpers.imu_preintegrator import ImuPreintegrator
+from gps_denied_onboard.helpers.ransac_filter import RansacFilter
+from gps_denied_onboard.helpers.wgs_converter import WgsConverter
+from gps_denied_onboard.runtime_root import airborne_bootstrap
+from gps_denied_onboard.runtime_root.airborne_bootstrap import (
+    AirborneBootstrapError,
+    build_pre_constructed,
+    clear_imu_preintegrator_cache,
+)
+
+
+def _config_with_calibration_path(path: str) -> Config:
+    """Return a fresh ``Config`` whose ``runtime.camera_calibration_path`` is set.
+
+    ``RuntimeConfig`` is a frozen dataclass; mutate via
+    :func:`dataclasses.replace` rather than ``object.__setattr__``.
+    """
+    base = Config()
+    runtime = dataclasses.replace(base.runtime, camera_calibration_path=path)
+    return dataclasses.replace(base, runtime=runtime)
+
+
+def _make_calibration(camera_id: str = "az623-test-camera") -> CameraCalibration:
+    """Sentinel CameraCalibration matching the C5 estimator's expected shape.
+
+    The bias / sample accumulator inside :class:`ImuPreintegrator` only
+    needs intrinsics-shape inputs to be present; AZ-623 tests do not
+    integrate samples, so the contents are irrelevant beyond passing
+    :func:`make_imu_preintegrator`'s own internal validators.
+    """
+    return CameraCalibration(
+        camera_id=camera_id,
+        intrinsics_3x3=np.eye(3, dtype=np.float64),
+        distortion=np.zeros(5, dtype=np.float64),
+        body_to_camera_se3=np.eye(4, dtype=np.float64),
+        acquisition_method="operator",
+        metadata={},
+    )
+
+
+@pytest.fixture(autouse=True)
+def _isolated_caches() -> Iterator[None]:
+    # Arrange: every test starts with empty FdrClient cache + empty
+    # ImuPreintegrator cache so AC-623.2's "same instance across calls"
+    # assertion is exercised against fresh state.
+    fdr_client_module._reset_for_tests()
+    clear_imu_preintegrator_cache()
+    yield
+    fdr_client_module._reset_for_tests()
+    clear_imu_preintegrator_cache()
+
+
+@pytest.fixture(autouse=True)
+def _stub_az619_to_az622_builders(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange: stub the AZ-619 (clock seeded by build_pre_constructed
+    # directly via WallClock — no builder), AZ-620 (Phase B) C6 builders,
+    # AZ-621 (Phase C) C7 inference builder, and AZ-622 (Phase D) C3
+    # builders so AZ-623 stays focused on the Phase E contract. Sentinels
+    # are opaque on purpose — AZ-623 assertions never inspect them.
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c6_descriptor_index",
+        lambda _config: MagicMock(name="DescriptorIndex"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c6_tile_store",
+        lambda _config: MagicMock(name="TileStore"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c7_inference",
+        lambda _config: MagicMock(name="InferenceRuntime"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c3_lightglue_runtime",
+        lambda _config, *, inference_runtime: MagicMock(name="LightGlueRuntime"),
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_build_c3_feature_extractor",
+        lambda _config: MagicMock(name="FeatureExtractor"),
+    )
+
+
+def test_ac_623_1_adds_c282_ransac_and_c5_helpers(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # Arrange: a Config with a populated camera_calibration_path so
+    # _build_c5_imu_preintegrator's empty-check passes. Stub
+    # _load_camera_calibration to return a sentinel calibration so the
+    # bootstrap does not touch the filesystem.
+    config = _config_with_calibration_path("/tmp/az623-fixture-calib.json")
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_load_camera_calibration",
+        lambda _config: _make_calibration(),
+    )
+
+    # Act
+    pre_constructed = build_pre_constructed(config)
+
+    # Assert: each new key is present and typed per AC-623.1.
+    assert "c282_ransac_filter" in pre_constructed
+    assert isinstance(pre_constructed["c282_ransac_filter"], RansacFilter)
+
+    assert "c5_imu_preintegrator" in pre_constructed
+    assert isinstance(pre_constructed["c5_imu_preintegrator"], ImuPreintegrator)
+
+    assert "c5_se3_utils" in pre_constructed
+    se3_utils = pre_constructed["c5_se3_utils"]
+    # The se3_utils handle is the helpers.se3_utils module — a module is
+    # the simplest namespace object that exposes exp_map, log_map etc.
+    # as attributes (matches the MagicMock fixture pattern existing C5
+    # tests already use).
+    assert se3_utils is se3_utils_module
+    for func_name in ("exp_map", "log_map", "matrix_to_se3", "se3_to_matrix"):
+        assert hasattr(se3_utils, func_name), (
+            f"c5_se3_utils handle is missing {func_name!r}; "
+            f"consumers (build_state_estimator, build_pose_estimator) "
+            f"dispatch via attribute access."
+        )
+
+    assert "c5_wgs_converter" in pre_constructed
+    assert isinstance(pre_constructed["c5_wgs_converter"], WgsConverter)
+
+
+def test_ac_623_1_keeps_existing_keys_intact(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange
+    config = _config_with_calibration_path("/tmp/az623-fixture-calib.json")
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_load_camera_calibration",
+        lambda _config: _make_calibration(),
+    )
+
+    # Act
+    pre_constructed = build_pre_constructed(config)
+
+    # Assert: AZ-619..AZ-622 keys remain populated; AZ-623 is additive.
+    assert {
+        "c13_fdr",
+        "clock",
+        "c6_descriptor_index",
+        "c6_tile_store",
+        "c7_inference",
+        "c3_lightglue_runtime",
+        "c3_feature_extractor",
+    }.issubset(pre_constructed.keys()), (
+        f"AZ-623 must be additive on top of AZ-619..AZ-622; got "
+        f"keys: {sorted(pre_constructed.keys())}"
+    )
+
+
+def test_ac_623_2_imu_preintegrator_cached_across_calls(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # Arrange: stub the calibration loader with a counter so we can
+    # assert the cache short-circuit fires on the second call.
+    config = _config_with_calibration_path("/tmp/az623-cache-fixture.json")
+    load_count = {"n": 0}
+
+    def _counting_load(_config: Config) -> CameraCalibration:
+        load_count["n"] += 1
+        return _make_calibration()
+
+    monkeypatch.setattr(airborne_bootstrap, "_load_camera_calibration", _counting_load)
+
+    # Act
+    first = build_pre_constructed(config)
+    second = build_pre_constructed(config)
+
+    # Assert: cache holds the same ImuPreintegrator instance; the
+    # calibration loader fires exactly once across the two calls.
+    assert first["c5_imu_preintegrator"] is second["c5_imu_preintegrator"], (
+        "AC-623.2 requires c5_imu_preintegrator to be the same instance "
+        "across two build_pre_constructed calls (cache keyed on "
+        "camera_calibration_path)"
+    )
+    assert load_count["n"] == 1, (
+        f"calibration loader should fire once (cached on second call); "
+        f"got {load_count['n']} invocations"
+    )
+
+
+def test_ac_623_2_imu_preintegrator_per_path_cache(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # Arrange: two configs with DIFFERENT calibration paths. The cache
+    # must produce DIFFERENT preintegrator instances (one per path).
+    config_a = _config_with_calibration_path("/tmp/az623-path-a.json")
+    config_b = _config_with_calibration_path("/tmp/az623-path-b.json")
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "_load_camera_calibration",
+        lambda _config: _make_calibration(),
+    )
+
+    # Act
+    a = build_pre_constructed(config_a)
+    b = build_pre_constructed(config_b)
+
+    # Assert
+    assert a["c5_imu_preintegrator"] is not b["c5_imu_preintegrator"], (
+        "Two distinct calibration paths must produce two distinct "
+        "ImuPreintegrator instances; the cache key is the path."
+    )
+
+
+def test_ac_623_3_empty_calibration_path_raises_named_error() -> None:
+    # Arrange: default Config() has camera_calibration_path="".
+    config = Config()
+
+    # Act + Assert
+    with pytest.raises(AirborneBootstrapError) as exc_info:
+        build_pre_constructed(config)
+    msg = str(exc_info.value)
+    assert "c5_imu_preintegrator" in msg, msg
+    assert "camera_calibration_path" in msg, msg
+    assert "c5_state" in msg, msg
+
+
+def test_ac_623_3_unreadable_calibration_path_raises_named_error(
+    tmp_path: Path,
+) -> None:
+    # Arrange: pass a path that does not exist on disk; the OSError
+    # surfaces as AirborneBootstrapError with the operator-actionable
+    # message.
+    missing = tmp_path / "this-file-does-not-exist.json"
+    config = _config_with_calibration_path(str(missing))
+
+    # Act + Assert
+    with pytest.raises(AirborneBootstrapError) as exc_info:
+        build_pre_constructed(config)
+    msg = str(exc_info.value)
+    assert "c5_imu_preintegrator" in msg
+    assert "c5_state" in msg
+    assert str(missing) in msg
+
+
+def test_ac_623_3_malformed_json_calibration_raises_named_error(
+    tmp_path: Path,
+) -> None:
+    # Arrange
+    bad = tmp_path / "bad-calib.json"
+    bad.write_text("{ this is not valid json", encoding="utf-8")
+    config = _config_with_calibration_path(str(bad))
+
+    # Act + Assert
+    with pytest.raises(AirborneBootstrapError) as exc_info:
+        build_pre_constructed(config)
+    msg = str(exc_info.value)
+    assert "c5_imu_preintegrator" in msg
+    assert "c5_state" in msg
+    assert "not valid JSON" in msg