[AZ-621] Phase C: build_pre_constructed seeds c7_inference

Third subtask of AZ-618. Extends airborne_bootstrap.build_pre_constructed
additively with c7_inference (GPU InferenceRuntime). Wraps the existing
inference_factory.build_inference_runtime so a BUILD_TENSORRT_RUNTIME /
BUILD_PYTORCH_FP16_RUNTIME mismatch surfaces a clear operator-facing
AirborneBootstrapError naming BOTH airborne C7 flags plus the consuming
component slug, rather than bubbling up RuntimeNotAvailableError with no
context.

New public const C7_AIRBORNE_BUILD_FLAGS pairs each airborne runtime
with its gating env flag (onnx_trt_ep deliberately omitted — research
only). Tests stub at the factory boundary; real GPU/TensorRT load
remains Tier-2 only (consolidated at AZ-624). AZ-619 and AZ-620 test
files extended with a _stub_c7_inference_builder autouse fixture
mirroring the AZ-620 pattern for _build_c6_*.

18/18 runtime_root unit tests pass.

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

src/gps_denied_onboard/runtime_root/airborne_bootstrap.py

@@ -57,6 +57,7 @@ from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.fdr_client.client import make_fdr_client
 from gps_denied_onboard.runtime_root import register_strategy
 from gps_denied_onboard.runtime_root.errors import RuntimeNotAvailableError
+from gps_denied_onboard.runtime_root.inference_factory import build_inference_runtime
 from gps_denied_onboard.runtime_root.matcher_factory import build_matcher_strategy
 from gps_denied_onboard.runtime_root.pose_factory import build_pose_estimator
 from gps_denied_onboard.runtime_root.refiner_factory import build_refiner_strategy
@@ -75,6 +76,7 @@ if TYPE_CHECKING:
 __all__ = [
     "AIRBORNE_MAIN_PRODUCER_ID",
     "AIRBORNE_REQUIRED_PRE_CONSTRUCTED_KEYS",
+    "C7_AIRBORNE_BUILD_FLAGS",
     "FAISS_BUILD_FLAG",
     "AirborneBootstrapError",
     "build_pre_constructed",
@@ -92,6 +94,26 @@ flag is OFF but a consuming component still requires the index.
 """
 
 
+C7_AIRBORNE_BUILD_FLAGS: Final[tuple[tuple[str, str], ...]] = (
+    ("tensorrt", "BUILD_TENSORRT_RUNTIME"),
+    ("pytorch_fp16", "BUILD_PYTORCH_FP16_RUNTIME"),
+)
+"""Airborne-buildable C7 inference runtimes paired with their gating env flags.
+
+Production-default for the airborne binary is ``tensorrt`` (TensorRT FP16);
+``pytorch_fp16`` is the Tier-0 / workstation fallback (per
+``module-layout.md`` build-time exclusion table and the AZ-621 task spec).
+``onnx_trt_ep`` is deliberately omitted — it is research-only and not built
+into the airborne binary, even though
+:mod:`gps_denied_onboard.runtime_root.inference_factory` supports the label.
+
+Surfaced here so :func:`_build_c7_inference` can name BOTH airborne flags
+in an :class:`AirborneBootstrapError` (AC-621.2) — the operator sees which
+flag must be flipped ON to enable the configured runtime AND which fallback
+flag would unblock the bootstrap with a different runtime selection.
+"""
+
+
 AIRBORNE_MAIN_PRODUCER_ID: Final[str] = "airborne_main"
 """Producer ID for the per-binary shared FdrClient placed under
 ``pre_constructed['c13_fdr']``.
@@ -474,22 +496,71 @@ def _build_c6_tile_store(config: Config) -> Any:
     return build_tile_store(config)
 
 
+def _build_c7_inference(config: Config) -> Any:
+    """Build ``pre_constructed['c7_inference']`` via the C7 factory.
+
+    Wraps :func:`inference_factory.build_inference_runtime` so a
+    :class:`RuntimeNotAvailableError` (raised when the configured
+    runtime's ``BUILD_*`` flag is OFF) surfaces as an
+    :class:`AirborneBootstrapError` naming:
+
+    * the missing key (``c7_inference``);
+    * BOTH airborne-buildable runtimes and their gating flags
+      (:data:`C7_AIRBORNE_BUILD_FLAGS`), so the operator sees the
+      production-default (``tensorrt`` /
+      ``BUILD_TENSORRT_RUNTIME``) AND the Tier-0 fallback
+      (``pytorch_fp16`` / ``BUILD_PYTORCH_FP16_RUNTIME``);
+    * the consuming component slug(s) — narrowed to configured
+      consumers when available, else the full theoretical set.
+
+    The original factory error is preserved via ``raise ... from`` so
+    operators still see the upstream cause (e.g., "runtime 'tensorrt'
+    requires BUILD_TENSORRT_RUNTIME=ON in this binary; the flag is
+    OFF.").
+
+    AC-621.2: this is the path the test exercises when both airborne C7
+    flags are OFF and a configured consumer (c2_vpr / c3_matcher /
+    c3_5_adhop) still needs ``c7_inference``.
+    """
+    try:
+        return build_inference_runtime(config)
+    except RuntimeNotAvailableError as exc:
+        consumers = _configured_consumers_of_pre_constructed_key(
+            config, "c7_inference"
+        )
+        flag_options = ", ".join(
+            f"{flag}=ON for runtime {runtime!r}"
+            for runtime, flag in C7_AIRBORNE_BUILD_FLAGS
+        )
+        raise AirborneBootstrapError(
+            f"airborne_bootstrap: cannot construct "
+            f"pre_constructed['c7_inference'] because no airborne C7 "
+            f"inference runtime is buildable. Consuming components: "
+            f"{list(consumers)}. Set one of: {flag_options}, and ensure "
+            f"config.components['c7_inference'].runtime matches the "
+            f"enabled flag. Upstream error: {exc}"
+        ) from exc
+
+
 def build_pre_constructed(config: Config) -> dict[str, Any]:
     """Build the airborne ``pre_constructed`` dict for :func:`compose_root`.
 
     AZ-619 (Phase A) seeded ``c13_fdr`` and ``clock``. AZ-620 (Phase B)
-    adds the two C6 storage entries (``c6_descriptor_index`` +
-    ``c6_tile_store``). Phases C..F (AZ-621..AZ-624) will extend this
-    function to populate the remaining keys in
+    added the two C6 storage entries (``c6_descriptor_index`` +
+    ``c6_tile_store``). AZ-621 (Phase C) adds ``c7_inference``
+    (PyTorch FP16 vs. TensorRT, gated by
+    :data:`C7_AIRBORNE_BUILD_FLAGS`). Phases D..F (AZ-622..AZ-624) will
+    extend this function to populate the remaining keys in
     :data:`AIRBORNE_REQUIRED_PRE_CONSTRUCTED_KEYS`.
 
     Returns a fresh dict on each call. The ``c13_fdr`` instance is cached
     inside :func:`make_fdr_client` (per-producer cache) so two calls within
     the same process return dicts where ``pre_constructed['c13_fdr']`` is
     the SAME object — AC-619.2. ``clock`` is a fresh :class:`WallClock`
-    each call (stateless; the cache would be a no-op). The C6 entries are
-    constructed via the existing :mod:`storage_factory` builders without
-    additional caching at this layer.
+    each call (stateless; the cache would be a no-op). The C6 + C7
+    entries are constructed via the existing :mod:`storage_factory` and
+    :mod:`inference_factory` builders without additional caching at this
+    layer.
 
     Replay-mode override: :func:`compose_root` merges ``replay_components``
     over ``pre_constructed`` so the :class:`WallClock` here is replaced by
@@ -500,14 +571,19 @@ def build_pre_constructed(config: Config) -> dict[str, Any]:
         AirborneBootstrapError: if ``BUILD_FAISS_INDEX`` is OFF and any
             configured consumer (per
             :data:`AIRBORNE_REQUIRED_PRE_CONSTRUCTED_KEYS`) requires
-            ``c6_descriptor_index`` — surfaces with the consuming
-            component slug(s) and the gating flag.
+            ``c6_descriptor_index``; OR if no airborne C7 inference
+            runtime is buildable (both ``BUILD_TENSORRT_RUNTIME`` and
+            ``BUILD_PYTORCH_FP16_RUNTIME`` OFF, or the configured
+            runtime's matching flag is OFF) and any configured consumer
+            requires ``c7_inference``. The message names the consuming
+            component slug(s) and the relevant gating flag(s).
     """
     return {
         "c13_fdr": make_fdr_client(AIRBORNE_MAIN_PRODUCER_ID, config),
         "clock": WallClock(),
         "c6_descriptor_index": _build_c6_descriptor_index(config),
         "c6_tile_store": _build_c6_tile_store(config),
+        "c7_inference": _build_c7_inference(config),
     }