[AZ-620] Phase B: build_pre_constructed seeds c6_descriptor_index + c6_tile_store

Second of six subtasks of AZ-618. Extends
airborne_bootstrap.build_pre_constructed(config) additively with the
two C6 storage entries on top of AZ-619's c13_fdr + clock contract:

- c6_descriptor_index: via storage_factory.build_descriptor_index
- c6_tile_store:       via storage_factory.build_tile_store

When BUILD_FAISS_INDEX=OFF, the lower-level RuntimeNotAvailableError
from the descriptor index factory is translated into an
AirborneBootstrapError that names the missing key
(c6_descriptor_index), the gating flag (BUILD_FAISS_INDEX), and the
consuming component slug(s) drawn from
AIRBORNE_REQUIRED_PRE_CONSTRUCTED_KEYS. The original error is
preserved as __cause__ so operators still see the upstream reason.

Tests: 3 new unit tests cover AC-620.1 + AC-620.2 (twice, with and
without a configured consumer, so the bootstrap fails loudly in
either branch). AZ-619 tests updated to add an autouse stub for the
Phase B builders (keeps them focused on Phase A keys) and to relax
the "exactly two keys" assertion to "AZ-619 keys remain present
under AZ-620 additivity" per the original test's own forward-pointer.

Bonus: ruff --fix removed 12 pre-existing UP037 quoted-annotation
warnings in airborne_bootstrap.py (covered by `from __future__ import
annotations`). All in modified-area scope per quality-gates.mdc.

Run: pytest tests/unit/runtime_root/ -q -> 15/15 passed in 1.06s.

Spec moved to _docs/02_tasks/done/ in the previous commit (audit-trail
backfill of batch_90 also landed there).

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

tests/unit/runtime_root/test_az619_pre_constructed_phase_a.py

@@ -1,7 +1,7 @@
 """AZ-619 — Phase A of AZ-618: ``build_pre_constructed`` seeds c13_fdr + clock.
 
 Verifies the contract at
-``_docs/02_tasks/todo/AZ-619_pre_constructed_phase_a_c13_fdr_clock.md``:
+``_docs/02_tasks/done/AZ-619_pre_constructed_phase_a_c13_fdr_clock.md``:
 
 * AC-619.1: ``build_pre_constructed(default_config)`` returns a dict
   containing keys ``c13_fdr`` (FdrClient instance) and ``clock``
@@ -12,6 +12,17 @@ Verifies the contract at
 
 AC-619.3 (this file exists with the above tests) is satisfied by the
 existence of this module.
+
+AZ-620 amendment: ``build_pre_constructed`` now also calls the C6
+storage factories (``build_descriptor_index`` + ``build_tile_store``)
+to populate ``c6_descriptor_index`` + ``c6_tile_store``. Those
+factories require ``config.components["c6_tile_cache"]`` to be present
+and (for the descriptor index) ``BUILD_FAISS_INDEX=ON``. The AZ-619
+tests use bare ``Config()`` — empty ``components`` — so we stub the C6
+builders with sentinel returns. This keeps the AZ-619 contract
+assertions focused on Phase A keys without entangling them with the
+heavier Phase B integration paths (those are covered by
+``test_az620_pre_constructed_phase_b.py``).
 """
 
 from __future__ import annotations
@@ -24,6 +35,7 @@ from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.config import Config
 from gps_denied_onboard.fdr_client import client as fdr_client_module
 from gps_denied_onboard.fdr_client.client import FdrClient
+from gps_denied_onboard.runtime_root import airborne_bootstrap
 from gps_denied_onboard.runtime_root.airborne_bootstrap import (
     AIRBORNE_MAIN_PRODUCER_ID,
     build_pre_constructed,
@@ -40,6 +52,21 @@ def _isolated_fdr_cache() -> Iterator[None]:
     fdr_client_module._reset_for_tests()
 
 
+@pytest.fixture(autouse=True)
+def _stub_c6_builders(monkeypatch: pytest.MonkeyPatch) -> None:
+    # Arrange: stub the AZ-620 Phase B C6 storage builders so the AZ-619
+    # tests stay focused on the Phase A contract. Without this the bare
+    # 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()
+    )
+
+
 def test_ac_619_1_default_config_seeds_c13_fdr_and_clock() -> None:
     # Arrange
     config = Config()
@@ -92,12 +119,14 @@ def test_ac_619_2_clock_is_independent_instance_per_call() -> None:
     assert isinstance(second["clock"], WallClock)
 
 
-def test_phase_a_only_seeds_two_keys() -> None:
-    """Phase A scope discipline: exactly the two documented keys.
+def test_phase_a_keys_remain_present_under_az620_additivity() -> None:
+    """Phase A's keys must survive AZ-620's additive extension.
 
-    Phases B..F (AZ-620..AZ-624) will add more keys; this test will be
-    relaxed at that point. For now it pins the AZ-619 contract precisely so
-    a regression that adds keys here without updating the spec is caught.
+    AZ-620 (Phase B) added ``c6_descriptor_index`` + ``c6_tile_store`` and
+    the spec mandates additivity ("MUST be additive on top of AZ-619" —
+    AZ-620 Constraints). The AZ-619 contract is therefore: ``c13_fdr`` and
+    ``clock`` MUST always be present in the dict, regardless of how many
+    later phases extend it.
     """
     # Arrange
     config = Config()
@@ -105,5 +134,9 @@ def test_phase_a_only_seeds_two_keys() -> None:
     # Act
     pre_constructed = build_pre_constructed(config)
 
-    # Assert
-    assert set(pre_constructed.keys()) == {"c13_fdr", "clock"}
+    # Assert: AZ-619 keys still there and correctly typed (the additivity
+    # contract). Other keys are allowed and validated by Phase B/C/D/E/F
+    # tests.
+    assert {"c13_fdr", "clock"}.issubset(pre_constructed.keys())
+    assert isinstance(pre_constructed["c13_fdr"], FdrClient)
+    assert isinstance(pre_constructed["clock"], WallClock)

tests/unit/runtime_root/test_az620_pre_constructed_phase_b.py

@@ -0,0 +1,168 @@
+"""AZ-620 — Phase B of AZ-618: ``build_pre_constructed`` seeds c6_descriptor_index + c6_tile_store.
+
+Verifies the contract at
+``_docs/02_tasks/todo/AZ-620_pre_constructed_phase_b_c6_storage.md``:
+
+* AC-620.1: with a default airborne ``Config`` (and ``BUILD_FAISS_INDEX=ON``),
+  ``build_pre_constructed(config)`` additionally contains
+  ``c6_descriptor_index`` (DescriptorIndex instance) and ``c6_tile_store``
+  (TileStore instance) on top of AZ-619's contract.
+* AC-620.2: when ``BUILD_FAISS_INDEX=OFF`` AND a config selects
+  ``c2_vpr.strategy="net_vlad"`` (a strategy that requires
+  ``c6_descriptor_index``), ``build_pre_constructed`` raises
+  ``AirborneBootstrapError`` whose message names ``c6_descriptor_index``
+  (the missing key), ``BUILD_FAISS_INDEX`` (the gating flag), and
+  ``c2_vpr`` (the consuming component slug).
+
+AC-620.3 (this file exists with the above tests) is satisfied by the
+existence of this module.
+
+The tests stub the heavy C6 factories (`build_descriptor_index`,
+`build_tile_store`) at the airborne_bootstrap import boundary. The C6
+factories themselves have their own unit tests under
+``tests/unit/c6_tile_cache/`` covering Postgres + FAISS internals; here
+we only validate the bootstrap-layer wiring and error translation.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Iterator
+from dataclasses import dataclass
+from unittest.mock import MagicMock
+
+import pytest
+
+from gps_denied_onboard.config import Config
+from gps_denied_onboard.fdr_client import client as fdr_client_module
+from gps_denied_onboard.runtime_root import airborne_bootstrap
+from gps_denied_onboard.runtime_root.airborne_bootstrap import (
+    FAISS_BUILD_FLAG,
+    AirborneBootstrapError,
+    build_pre_constructed,
+)
+from gps_denied_onboard.runtime_root.errors import RuntimeNotAvailableError
+
+
+@dataclass(frozen=True)
+class _C2VprBlock:
+    """Minimal c2_vpr config block — only the field the test needs."""
+
+    strategy: str = "net_vlad"
+
+
+@pytest.fixture(autouse=True)
+def _isolated_fdr_cache() -> Iterator[None]:
+    # Arrange: every test starts with an empty FdrClient cache so the
+    # bootstrap's make_fdr_client call doesn't accidentally pick up a
+    # stale instance from a prior test in the same process.
+    fdr_client_module._reset_for_tests()
+    yield
+    fdr_client_module._reset_for_tests()
+
+
+def test_ac_620_1_adds_c6_descriptor_index_and_c6_tile_store(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # Arrange: stub the c6 factories to return identifiable sentinels so we
+    # can assert wiring without standing up real FAISS + Postgres.
+    descriptor_index_sentinel = MagicMock(name="DescriptorIndex")
+    tile_store_sentinel = MagicMock(name="TileStore")
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "build_descriptor_index",
+        lambda _config: descriptor_index_sentinel,
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "build_tile_store",
+        lambda _config: tile_store_sentinel,
+    )
+    config = Config()
+
+    # Act
+    pre_constructed = build_pre_constructed(config)
+
+    # Assert: AZ-620 keys are present and reference the exact factory
+    # returns. AZ-619 keys are still present (additivity contract).
+    assert "c6_descriptor_index" in pre_constructed
+    assert "c6_tile_store" in pre_constructed
+    assert pre_constructed["c6_descriptor_index"] is descriptor_index_sentinel
+    assert pre_constructed["c6_tile_store"] is tile_store_sentinel
+    assert "c13_fdr" in pre_constructed
+    assert "clock" in pre_constructed
+
+
+def test_ac_620_2_build_flag_off_with_configured_c2_vpr_raises_named_error(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # Arrange: simulate BUILD_FAISS_INDEX=OFF by making the c6 descriptor
+    # factory raise RuntimeNotAvailableError the same way storage_factory
+    # does in production. Tile store stays stubbed so the test is focused
+    # on the descriptor-index translation path.
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "build_descriptor_index",
+        _raise_faiss_disabled,
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "build_tile_store",
+        lambda _config: MagicMock(name="TileStore"),
+    )
+    config = Config.with_blocks(c2_vpr=_C2VprBlock(strategy="net_vlad"))
+
+    # Act + Assert
+    with pytest.raises(AirborneBootstrapError) as excinfo:
+        build_pre_constructed(config)
+
+    message = str(excinfo.value)
+    assert "c6_descriptor_index" in message
+    assert FAISS_BUILD_FLAG in message
+    assert "c2_vpr" in message
+    # The original factory error is preserved as the cause chain so the
+    # operator can still see the upstream reason.
+    assert isinstance(excinfo.value.__cause__, RuntimeNotAvailableError)
+
+
+def test_ac_620_2_no_configured_consumer_still_raises_with_full_set(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """Defence-in-depth: even with no consumer configured, AZ-620 still
+    fails loudly when BUILD_FAISS_INDEX is OFF.
+
+    Rationale: ``build_pre_constructed`` is the airborne contract's single
+    seam — silently returning a dict without ``c6_descriptor_index`` would
+    let a later AZ-621..AZ-624 phase or a downstream caller misread the
+    state. The error message in this case lists the FULL theoretical
+    consumer set so the operator still gets actionable information.
+    """
+    # Arrange
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "build_descriptor_index",
+        _raise_faiss_disabled,
+    )
+    monkeypatch.setattr(
+        airborne_bootstrap,
+        "build_tile_store",
+        lambda _config: MagicMock(name="TileStore"),
+    )
+    config = Config()  # empty components
+
+    # Act + Assert
+    with pytest.raises(AirborneBootstrapError) as excinfo:
+        build_pre_constructed(config)
+
+    message = str(excinfo.value)
+    assert "c6_descriptor_index" in message
+    assert FAISS_BUILD_FLAG in message
+    # When no consumer is configured, ALL theoretical consumers
+    # of c6_descriptor_index are surfaced — currently {c2_vpr}.
+    assert "c2_vpr" in message
+
+
+def _raise_faiss_disabled(_config: Config) -> None:
+    raise RuntimeNotAvailableError(
+        f"DescriptorIndex runtime 'faiss_hnsw' requires "
+        f"{FAISS_BUILD_FLAG}=ON in this binary; the flag is OFF."
+    )