[AZ-526] Consolidate _iso_ts_from_clock into helpers/iso_timestamps

Closes cumulative review 46-48 F1 (Medium) + F3 (Low). Adds
iso_ts_from_clock(clock) alongside iso_ts_now() in the Layer-1
helper; migrates four duplicate definitions in c2_vpr (net_vlad,
ultra_vpr, _faiss_bridge) and c12_operator_orchestrator
(operator_reloc_service). Output format flipped +00:00 -> Z to
align with iso_ts_now() and the canonical FDR _TS fixture (FDR
schema test passes unmodified).

18 helper AC tests + 186 sibling tests pass; ruff clean.

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

src/gps_denied_onboard/components/c12_operator_orchestrator/operator_reloc_service.py

@@ -14,7 +14,6 @@ auto-retried. The operator decides when to re-issue.
 from __future__ import annotations
 
 import logging
-from datetime import datetime, timezone
 
 from gps_denied_onboard.clock import Clock
 from gps_denied_onboard.components.c12_operator_orchestrator._types import (
@@ -31,6 +30,7 @@ from gps_denied_onboard.fdr_client.records import (
     CURRENT_SCHEMA_VERSION,
     FdrRecord,
 )
+from gps_denied_onboard.helpers.iso_timestamps import iso_ts_from_clock
 
 __all__ = ["OperatorReLocService"]
 
@@ -165,10 +165,7 @@ class OperatorReLocService:
             )
 
     def _iso_ts_from_clock(self) -> str:
-        ns = int(self._clock.time_ns())
-        seconds, fraction_ns = divmod(ns, 1_000_000_000)
-        dt = datetime.fromtimestamp(seconds, tz=timezone.utc)
-        return f"{dt.strftime('%Y-%m-%dT%H:%M:%S')}.{fraction_ns:09d}+00:00"
+        return iso_ts_from_clock(self._clock)
 
 
 def _hint_to_payload(hint: ReLocHint) -> dict[str, object]:

src/gps_denied_onboard/components/c2_vpr/_faiss_bridge.py

@@ -48,6 +48,7 @@ from gps_denied_onboard.fdr_client.records import (
     CURRENT_SCHEMA_VERSION,
     FdrRecord,
 )
+from gps_denied_onboard.helpers.iso_timestamps import iso_ts_from_clock
 
 if TYPE_CHECKING:
     pass
@@ -304,14 +305,4 @@ class FaissBridge:
             )
 
     def _iso_ts_from_clock(self) -> str:
-        # Inlined here rather than importing a shared helper because every
-        # other component that emits FDR records (c12, c11, c5) defines
-        # the same one-liner locally — see meta-rule "Critical Thinking":
-        # the duplication is intentional and trivial, factoring it would
-        # add an L1 import every component already avoids.
-        from datetime import datetime, timezone
-
-        ns = int(self._clock.time_ns())
-        seconds, fraction_ns = divmod(ns, 1_000_000_000)
-        dt = datetime.fromtimestamp(seconds, tz=timezone.utc)
-        return f"{dt.strftime('%Y-%m-%dT%H:%M:%S')}.{fraction_ns:09d}+00:00"
+        return iso_ts_from_clock(self._clock)

src/gps_denied_onboard/components/c2_vpr/net_vlad.py

@@ -105,6 +105,9 @@ from gps_denied_onboard.fdr_client.records import (
     FdrRecord,
 )
 from gps_denied_onboard.helpers.descriptor_normaliser import DescriptorNormaliser
+from gps_denied_onboard.helpers.iso_timestamps import (
+    iso_ts_from_clock as _iso_ts_from_clock,
+)
 
 if TYPE_CHECKING:
     from gps_denied_onboard._types.calibration import CameraCalibration
@@ -372,17 +375,6 @@ class NetVladStrategy:
         )
 
 
-def _iso_ts_from_clock(clock: Clock) -> str:
-    # Same shape every component uses for FDR timestamps; AZ-508 will
-    # consolidate the duplicate helpers across c2/c11/c12/c6.
-    from datetime import datetime, timezone
-
-    ns = int(clock.time_ns())
-    seconds, fraction_ns = divmod(ns, 1_000_000_000)
-    dt = datetime.fromtimestamp(seconds, tz=timezone.utc)
-    return f"{dt.strftime('%Y-%m-%dT%H:%M:%S')}.{fraction_ns:09d}+00:00"
-
-
 def _build_pytorch_build_config(weights_path: Path) -> BuildConfig:
     del weights_path
     return BuildConfig(

src/gps_denied_onboard/components/c2_vpr/ultra_vpr.py

@@ -84,6 +84,9 @@ from gps_denied_onboard.fdr_client.records import (
     FdrRecord,
 )
 from gps_denied_onboard.helpers.descriptor_normaliser import DescriptorNormaliser
+from gps_denied_onboard.helpers.iso_timestamps import (
+    iso_ts_from_clock as _iso_ts_from_clock,
+)
 
 if TYPE_CHECKING:
     from gps_denied_onboard._types.calibration import CameraCalibration
@@ -323,17 +326,6 @@ class UltraVprStrategy:
         )
 
 
-def _iso_ts_from_clock(clock: Clock) -> str:
-    # Same shape every component uses for FDR timestamps; AZ-508 will
-    # consolidate the duplicate helpers across c2/c11/c12/c6.
-    from datetime import datetime, timezone
-
-    ns = int(clock.time_ns())
-    seconds, fraction_ns = divmod(ns, 1_000_000_000)
-    dt = datetime.fromtimestamp(seconds, tz=timezone.utc)
-    return f"{dt.strftime('%Y-%m-%dT%H:%M:%S')}.{fraction_ns:09d}+00:00"
-
-
 def _build_trt_build_config() -> BuildConfig:
     return BuildConfig(
         precision=PrecisionMode.FP16,

src/gps_denied_onboard/helpers/__init__.py

@@ -22,7 +22,10 @@ from gps_denied_onboard.helpers.imu_preintegrator import (
     ImuPreintegrator,
     make_imu_preintegrator,
 )
-from gps_denied_onboard.helpers.iso_timestamps import iso_ts_now
+from gps_denied_onboard.helpers.iso_timestamps import (
+    iso_ts_from_clock,
+    iso_ts_now,
+)
 from gps_denied_onboard.helpers.lightglue_runtime import (
     LightGlueConcurrentAccessError,
     LightGlueRuntime,
@@ -84,6 +87,7 @@ __all__ = [
     "adjoint",
     "exp_map",
     "is_valid_rotation",
+    "iso_ts_from_clock",
     "iso_ts_now",
     "log_map",
     "make_imu_preintegrator",

src/gps_denied_onboard/helpers/iso_timestamps.py

@@ -1,27 +1,36 @@
-"""UTC ISO-8601 timestamp helper (E-CC-HELPERS / AZ-264 / AZ-508).
+"""UTC ISO-8601 timestamp helpers (E-CC-HELPERS / AZ-264 / AZ-508 + AZ-526).
 
-Single Layer-1 source for the wall-clock string used in the FDR record
-``ts`` envelope across c6_tile_cache and c7_inference. Consolidates what
-used to be a private ``_iso_ts_now`` one-liner repeated per module.
+Single Layer-1 source for the FDR record ``ts`` envelope strings across
+every component. Two variants:
 
-The output format is locked to RFC 3339 / ISO 8601 UTC with microsecond
-precision and a ``Z`` suffix, matching the canonical FDR ``ts`` fixture
-in ``tests/unit/test_az272_fdr_record_schema.py`` (``_TS =
-"2026-05-11T00:00:00.000000Z"``) and the format produced by the three
-existing local helpers this module replaces. Changing the format would
-alter FDR record bit-shape and is explicitly out of scope for AZ-508.
+- :func:`iso_ts_now` — uses :func:`datetime.now` (wall clock); 6-digit
+  microsecond precision; for components that don't have a ``Clock``
+  injected (the c6_tile_cache and c7_inference FDR producers).
+- :func:`iso_ts_from_clock` — uses an injected :class:`Clock` Protocol;
+  9-digit nanosecond precision; for components that already accept a
+  ``Clock`` constructor parameter (the c2_vpr strategies, the FAISS
+  bridge, the C12 operator-reloc service, and the future C4 / C5 batches).
 
-Producers that need a Clock-injected payload field (e.g.
-``age_seconds`` derived from an injected wall-clock for testability)
-MUST NOT route through this helper — it is purely metadata about WHEN
-the FDR record envelope itself was emitted.
+Both produce RFC 3339 UTC with a ``Z`` suffix, matching the canonical
+FDR ``ts`` fixture in ``tests/unit/test_az272_fdr_record_schema.py``
+(``_TS = "2026-05-11T00:00:00.000000Z"``). Changing the format would
+alter FDR record bit-shape and is explicitly out of scope.
+
+Producers that need a Clock-injected payload field (e.g. ``age_seconds``
+derived from an injected wall-clock for testability) MUST NOT route
+through these helpers — they are purely metadata about WHEN the FDR
+record envelope itself was emitted.
 """
 
 from __future__ import annotations
 
 from datetime import datetime, timezone
+from typing import TYPE_CHECKING
 
-__all__ = ["iso_ts_now"]
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
+
+__all__ = ["iso_ts_from_clock", "iso_ts_now"]
 
 
 def iso_ts_now() -> str:
@@ -31,3 +40,17 @@ def iso_ts_now() -> str:
     monotonic under a non-decreasing wall clock).
     """
     return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%S.%fZ")
+
+
+def iso_ts_from_clock(clock: Clock) -> str:
+    """Return an RFC 3339 UTC timestamp built from ``clock.time_ns()``.
+
+    Format: ``YYYY-MM-DDTHH:MM:SS.fffffffffZ`` (9-digit nanosecond
+    precision, ``Z`` suffix). Use when the timestamp must follow an
+    injectable :class:`~gps_denied_onboard.clock.Clock` (replay tests,
+    deterministic fixtures); use :func:`iso_ts_now` otherwise.
+    """
+    ns = int(clock.time_ns())
+    seconds, fraction_ns = divmod(ns, 1_000_000_000)
+    dt = datetime.fromtimestamp(seconds, tz=timezone.utc)
+    return f"{dt.strftime('%Y-%m-%dT%H:%M:%S')}.{fraction_ns:09d}Z"