diff --git a/pyproject.toml b/pyproject.toml
index 221a019..8b8cde8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,9 +17,11 @@ dependencies = [
     "diskcache>=5.6",
     "numpy>=1.26,<2.0",  # NumPy 2.0 silently breaks GTSAM Python bindings (issue #2264)
     "opencv-python-headless>=4.9,<4.11",  # 4.11+ requires numpy>=2.0 (incompatible with GTSAM)
+    "orjson>=3.10",
     "gtsam>=4.3a0",
     "pymavlink>=2.4",
     "pyyaml>=6.0",
+    "structlog>=25.1,<26",
 ]
 
 [project.optional-dependencies]
@@ -53,8 +55,19 @@ select = ["E", "F", "I", "W"]
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 asyncio_mode = "auto"
+# --strict-markers makes unregistered @pytest.mark.<x> fail collection rather than warn.
+# Per Phase 2 / TEST-02 contract; do not weaken without an explicit Phase 2 retrospective entry.
+addopts = "--strict-markers"
 markers = [
-    "e2e: end-to-end test against a real dataset",
+    # Phase 2 / TEST-01 taxonomy
+    "unit: pure-math or single-class test; only mocks; no I/O / no real DB / no real engines / no SITL; runs in <1s",
+    "integration: cross-subsystem (in-memory SQLite, ASGI transport, full FlightProcessor wiring across >=3 real components); no external process",
+    "blackbox: validates an external contract (e.g. MAVLink GPS_INPUT wire encoding per MAVLink #232) without a live producer",
+    "sitl: requires ARDUPILOT_SITL_HOST env var; talks to an ArduPilot SITL process over MAVLink; nightly-only",
+    "e2e: full-pipeline run against a real dataset (EuRoC, VPAIR, MARS-LVIG, Azaion) or its synthetic stand-in via E2EHarness; nightly-only",
+    # Phase 2 / TEST-03 traceability
+    "ac(ac_id): link test to one or more Acceptance Criteria (e.g. AC-1.1, AC-NEW-3); validated against _docs/00_problem/acceptance_criteria.md by scripts/gen_ac_traceability.py",
+    # Pre-existing (kept verbatim)
     "e2e_slow: e2e test that takes > 2 minutes, nightly-only",
     "needs_dataset: test requires an external dataset to be downloaded",
 ]
diff --git a/src/gps_denied/app.py b/src/gps_denied/app.py
index e49db2f..9ec6262 100644
--- a/src/gps_denied/app.py
+++ b/src/gps_denied/app.py
@@ -8,6 +8,7 @@ from fastapi import FastAPI
 from gps_denied import __version__
 from gps_denied.api.routers import flights
 from gps_denied.config import RuntimeConfig
+from gps_denied.obs import configure_logging
 from gps_denied.pipeline import build_pipeline
 
 logger = logging.getLogger(__name__)
@@ -17,6 +18,9 @@ logger = logging.getLogger(__name__)
 async def lifespan(app: FastAPI):
     """Initialise core pipeline components on startup via build_pipeline."""
     cfg = RuntimeConfig()
+    # OBS-01: configure structlog ONCE before pipeline construction.
+    # Non-hot-path logging (api/, db/) continues to use stdlib until Phase 6.
+    configure_logging(env=cfg.env)
     processor = build_pipeline(env=cfg.env, config=cfg)
 
     # Retrieve MAVLink bridge from processor internals for lifecycle management
diff --git a/src/gps_denied/components/mavlink_io/pymavlink_bridge.py b/src/gps_denied/components/mavlink_io/pymavlink_bridge.py
index 9317713..4a9a6d2 100644
--- a/src/gps_denied/components/mavlink_io/pymavlink_bridge.py
+++ b/src/gps_denied/components/mavlink_io/pymavlink_bridge.py
@@ -7,12 +7,12 @@ The legacy import path (gps_denied.core.mavlink) re-exports everything here.
 from __future__ import annotations
 
 import asyncio
-import logging
 import math
 import time
 from typing import Callable, Optional
 
 import numpy as np
+import structlog
 
 from gps_denied.schemas import GPSPoint
 from gps_denied.schemas.eskf import ConfidenceTier, ESKFState, IMUMeasurement
@@ -22,7 +22,7 @@ from gps_denied.schemas.mavlink import (
     TelemetryMessage,
 )
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 # ---------------------------------------------------------------------------
 # pymavlink conditional import
@@ -30,11 +30,11 @@ logger = logging.getLogger(__name__)
 try:
     from pymavlink import mavutil as _mavutil  # type: ignore
     _PYMAVLINK_AVAILABLE = True
-    logger.info("pymavlink available — real MAVLink connection enabled")
+    logger.info("pymavlink_available", mode="real_mavlink")
 except ImportError:
     _mavutil = None  # type: ignore
     _PYMAVLINK_AVAILABLE = False
-    logger.info("pymavlink not available — using MockMAVConnection (dev/CI mode)")
+    logger.info("pymavlink_unavailable", fallback="MockMAVConnection")
 
 # GPS epoch offset from Unix epoch (seconds)
 _GPS_EPOCH_OFFSET = 315_964_800
@@ -211,7 +211,7 @@ class MAVLinkBridge:
             asyncio.create_task(self._imu_receive_loop(), name="mav_imu_input"),
             asyncio.create_task(self._telemetry_loop(), name="mav_telemetry"),
         ]
-        logger.info("MAVLinkBridge started (conn=%s, %g Hz)", self.connection_string, self.output_hz)
+        logger.info("mavlink_bridge_started", conn=self.connection_string, output_hz=self.output_hz)
 
     async def stop(self) -> None:
         """Cancel background tasks and close connection."""
@@ -223,8 +223,7 @@ class MAVLinkBridge:
         if self._conn:
             self._conn.close()
             self._conn = None
-        logger.info("MAVLinkBridge stopped. sent=%d imu_rx=%d",
-                    self._sent_count, self._recv_imu_count)
+        logger.info("mavlink_bridge_stopped", sent=self._sent_count, imu_rx=self._recv_imu_count)
 
     def build_gps_input(self) -> Optional[GPSInputMessage]:
         """Build GPSInputMessage from current ESKF state (public, for testing)."""
@@ -238,6 +237,7 @@ class MAVLinkBridge:
 
     async def _gps_output_loop(self) -> None:
         """Send GPS_INPUT at output_hz.  MAV-01 / MAV-02."""
+        log = logger.bind(task="gps_output_loop")
         interval = 1.0 / self.output_hz
         while self._running:
             try:
@@ -250,7 +250,7 @@ class MAVLinkBridge:
                     if self._consecutive_failures >= self.max_consecutive_failures:
                         self._send_reloc_request()
             except Exception as exc:
-                logger.warning("GPS output loop error: %s", exc)
+                log.warning("gps_output_loop_error", error=str(exc))
             await asyncio.sleep(interval)
 
     def _send_gps_input(self, msg: GPSInputMessage) -> None:
@@ -289,7 +289,7 @@ class MAVLinkBridge:
                     lon=msg.lon,
                 )
         except Exception as exc:
-            logger.error("Failed to send GPS_INPUT: %s", exc)
+            logger.error("gps_input_send_failed", error=str(exc))
 
     # ------------------------------------------------------------------
     # MAV-03: IMU receive loop
@@ -297,6 +297,7 @@ class MAVLinkBridge:
 
     async def _imu_receive_loop(self) -> None:
         """Receive ATTITUDE/RAW_IMU and invoke ESKF callback.  MAV-03."""
+        log = logger.bind(task="imu_receive_loop")
         while self._running:
             try:
                 raw = self._recv_imu()
@@ -305,7 +306,7 @@ class MAVLinkBridge:
                     if self._on_imu:
                         self._on_imu(raw)
             except Exception as exc:
-                logger.warning("IMU receive loop error: %s", exc)
+                log.warning("imu_receive_loop_error", error=str(exc))
             await asyncio.sleep(0.01)  # poll at ~100 Hz; blocks throttled by recv_match timeout
 
     def _recv_imu(self) -> Optional[IMUMeasurement]:
@@ -334,7 +335,7 @@ class MAVLinkBridge:
                 timestamp=t,
             )
         except Exception as exc:
-            logger.debug("IMU recv error: %s", exc)
+            logger.debug("imu_recv_error", error=str(exc))
             return None
 
     # ------------------------------------------------------------------
@@ -364,9 +365,9 @@ class MAVLinkBridge:
                     )
                 else:
                     self._conn.named_value_float_send(time=t_boot_ms, name=name, value=value)
-            logger.warning("Re-localisation request sent (failures=%d)", self._consecutive_failures)
+            logger.warning("reloc_request_sent", consecutive_failures=self._consecutive_failures)
         except Exception as exc:
-            logger.error("Failed to send reloc request: %s", exc)
+            logger.error("reloc_request_send_failed", error=str(exc))
 
     def _build_reloc_request(self) -> RelocalizationRequest:
         last_lat, last_lon = None, None
@@ -393,13 +394,14 @@ class MAVLinkBridge:
 
     async def _telemetry_loop(self) -> None:
         """Send confidence + drift at 1 Hz.  MAV-05."""
+        log = logger.bind(task="telemetry_loop")
         interval = 1.0 / self.telemetry_hz
         while self._running:
             try:
                 self._send_telemetry()
                 self._frames_since_sat += 1
             except Exception as exc:
-                logger.warning("Telemetry loop error: %s", exc)
+                log.warning("telemetry_loop_error", error=str(exc))
             await asyncio.sleep(interval)
 
     def _send_telemetry(self) -> None:
@@ -437,7 +439,7 @@ class MAVLinkBridge:
                 else:
                     self._conn.named_value_float_send(time=t_boot_ms, name=name, value=float(value))
             except Exception as exc:
-                logger.debug("Telemetry send error: %s", exc)
+                logger.debug("telemetry_send_error", error=str(exc))
 
     # ------------------------------------------------------------------
     # Connection factory
@@ -448,8 +450,8 @@ class MAVLinkBridge:
         if _PYMAVLINK_AVAILABLE:
             try:
                 conn = _mavutil.mavlink_connection(self.connection_string)
-                logger.info("MAVLink connection opened: %s", self.connection_string)
+                logger.info("mavlink_connection_opened", conn=self.connection_string)
                 return conn
             except Exception as exc:
-                logger.warning("Cannot open MAVLink connection (%s) — using mock", exc)
+                logger.warning("mavlink_connection_failed", error=str(exc), fallback="mock")
         return MockMAVConnection()
diff --git a/src/gps_denied/components/satellite_matcher/local_tile_loader.py b/src/gps_denied/components/satellite_matcher/local_tile_loader.py
index 1ebf607..9b9fe04 100644
--- a/src/gps_denied/components/satellite_matcher/local_tile_loader.py
+++ b/src/gps_denied/components/satellite_matcher/local_tile_loader.py
@@ -1,18 +1,20 @@
 """Local-disk tile loader (SAT-01/02). Phase 1 home of the existing SatelliteDataManager impl."""
 
 import hashlib
-import logging
 import math
 import os
 from concurrent.futures import ThreadPoolExecutor
 
 import cv2
 import numpy as np
+import structlog
 
 from gps_denied.schemas import GPSPoint
 from gps_denied.schemas.satellite import TileBounds, TileCoords
 from gps_denied.utils import mercator
 
+logger = structlog.get_logger(__name__)
+
 
 class SatelliteDataManager:
     """Manages satellite tiles from a local pre-loaded directory.
@@ -24,8 +26,6 @@ class SatelliteDataManager:
     downloads and stores tiles before the mission.
     """
 
-    _logger = logging.getLogger(__name__)
-
     def __init__(
         self,
         tile_dir: str = ".satellite_tiles",
@@ -73,8 +73,10 @@ class SatelliteDataManager:
                 sha.update(chunk)
         actual = sha.hexdigest()
         if actual != expected:
-            self._logger.warning("Tile integrity failed: %s (exp %s, got %s)",
-                                rel_path, expected[:12], actual[:12])
+            logger.warning("tile_integrity_failed",
+                           rel_path=rel_path,
+                           expected_prefix=expected[:12],
+                           actual_prefix=actual[:12])
             return False
         return True
 
diff --git a/src/gps_denied/components/satellite_matcher/metric_refinement.py b/src/gps_denied/components/satellite_matcher/metric_refinement.py
index aeb8cd9..1efd22b 100644
--- a/src/gps_denied/components/satellite_matcher/metric_refinement.py
+++ b/src/gps_denied/components/satellite_matcher/metric_refinement.py
@@ -4,11 +4,11 @@ SAT-03: GSD normalization — downsample camera frame to satellite resolution.
 SAT-04: RANSAC homography → WGS84 position; confidence = inlier_ratio.
 """
 
-import logging
 from typing import List, Optional, Tuple
 
 import cv2
 import numpy as np
+import structlog
 
 from gps_denied.components.satellite_matcher.protocol import IMetricRefinement
 from gps_denied.core.models import IModelManager
@@ -16,7 +16,7 @@ from gps_denied.schemas import GPSPoint
 from gps_denied.schemas.metric import AlignmentResult, ChunkAlignmentResult, Sim3Transform
 from gps_denied.schemas.satellite import TileBounds
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 class MetricRefinement(IMetricRefinement):
diff --git a/src/gps_denied/components/vio/cuvslam_backend.py b/src/gps_denied/components/vio/cuvslam_backend.py
index 2c5d212..e7ee070 100644
--- a/src/gps_denied/components/vio/cuvslam_backend.py
+++ b/src/gps_denied/components/vio/cuvslam_backend.py
@@ -19,17 +19,17 @@ hardware; Inertial mode is retained for sprint-1 reversibility.
 """
 from __future__ import annotations
 
-import logging
 from typing import Optional
 
 import numpy as np
+import structlog
 
 from gps_denied.components.vio.orbslam_backend import ORBVisualOdometry
 from gps_denied.components.vio.protocol import ISequentialVisualOdometry
 from gps_denied.schemas import CameraParameters
 from gps_denied.schemas.vo import Features, Matches, Motion, RelativePose
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 # ---------------------------------------------------------------------------
 # Optional cuVSLAM SDK import (aarch64 Jetson only — x86 dev/CI must still pass)
@@ -70,9 +70,9 @@ class CuVSLAMVisualOdometry(ISequentialVisualOdometry):
             import cuvslam  # type: ignore  # only available on Jetson
             self._cuvslam = cuvslam
             self._init_tracker()
-            logger.info("CuVSLAMVisualOdometry: cuVSLAM SDK loaded (Jetson mode)")
+            logger.info("cuvslam_sdk_loaded", backend="CuVSLAMVisualOdometry", mode="jetson")
         except ImportError:
-            logger.info("CuVSLAMVisualOdometry: cuVSLAM not available — using ORB fallback (dev/CI mode)")
+            logger.info("cuvslam_sdk_unavailable", backend="CuVSLAMVisualOdometry", fallback="ORB")
 
     def _init_tracker(self):
         """Initialise cuVSLAM tracker in Inertial mode."""
@@ -96,9 +96,9 @@ class CuVSLAMVisualOdometry(ISequentialVisualOdometry):
                 gyro_noise=self._imu_params.get("gyro_noise", 0.001),
             )
             self._tracker = self._cuvslam.Tracker(rig_params, tracker_params)
-            logger.info("cuVSLAM tracker initialised in Inertial mode")
+            logger.info("cuvslam_tracker_initialised", mode="inertial")
         except Exception as exc:
-            logger.error("cuVSLAM tracker init failed: %s", exc)
+            logger.error("cuvslam_tracker_init_failed", error=str(exc))
             self._cuvslam = None
 
     @property
@@ -156,7 +156,7 @@ class CuVSLAMVisualOdometry(ISequentialVisualOdometry):
                 scale_ambiguous=False,  # VO-04: cuVSLAM Inertial mode = metric NED
             )
         except Exception as exc:
-            logger.error("cuVSLAM tracking step failed: %s", exc)
+            logger.error("cuvslam_tracking_step_failed", error=str(exc))
             return None
 
 
@@ -205,9 +205,9 @@ class CuVSLAMMonoDepthVisualOdometry(ISequentialVisualOdometry):
             import cuvslam  # type: ignore
             self._cuvslam = cuvslam
             self._init_tracker()
-            logger.info("CuVSLAMMonoDepthVisualOdometry: cuVSLAM SDK loaded (Jetson Mono-Depth mode)")
+            logger.info("cuvslam_sdk_loaded", backend="CuVSLAMMonoDepthVisualOdometry", mode="mono_depth")
         except ImportError:
-            logger.info("CuVSLAMMonoDepthVisualOdometry: cuVSLAM not available — using scaled ORB fallback")
+            logger.info("cuvslam_sdk_unavailable", backend="CuVSLAMMonoDepthVisualOdometry", fallback="scaled_ORB")
 
     def update_depth_hint(self, depth_hint_m: float) -> None:
         """Update barometric altitude used for scale recovery. Call each frame."""
@@ -231,11 +231,11 @@ class CuVSLAMMonoDepthVisualOdometry(ISequentialVisualOdometry):
             tracker_params.use_imu = False
             tracker_params.odometry_mode = self._cuvslam.OdometryMode.MONO_DEPTH
             self._tracker = self._cuvslam.Tracker(rig_params, tracker_params)
-            logger.info("cuVSLAM tracker initialised in Mono-Depth mode")
+            logger.info("cuvslam_tracker_initialised", mode="mono_depth")
         except Exception:
             logger.exception(
-                "cuVSLAM Mono-Depth tracker init FAILED — falling back to ORB. "
-                "Production Jetson path is DISABLED until this is fixed."
+                "cuvslam_mono_depth_init_failed",
+                note="Production Jetson path is DISABLED until this is fixed.",
             )
             self._cuvslam = None
 
@@ -277,7 +277,7 @@ class CuVSLAMMonoDepthVisualOdometry(ISequentialVisualOdometry):
                 scale_ambiguous=False,
             )
         except Exception:
-            logger.exception("cuVSLAM Mono-Depth tracking step failed — frame dropped")
+            logger.exception("cuvslam_mono_depth_tracking_failed", note="frame dropped")
             return None
 
     def _compute_via_orb_scaled(
diff --git a/src/gps_denied/components/vio/orbslam_backend.py b/src/gps_denied/components/vio/orbslam_backend.py
index 6ef5b56..25cb869 100644
--- a/src/gps_denied/components/vio/orbslam_backend.py
+++ b/src/gps_denied/components/vio/orbslam_backend.py
@@ -14,18 +14,18 @@ optional-import block isolated.
 """
 from __future__ import annotations
 
-import logging
 from typing import Optional
 
 import cv2
 import numpy as np
+import structlog
 
 from gps_denied.components.vio.protocol import ISequentialVisualOdometry
 from gps_denied.core.models import IModelManager
 from gps_denied.schemas import CameraParameters
 from gps_denied.schemas.vo import Features, Matches, Motion, RelativePose
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 class SequentialVisualOdometry(ISequentialVisualOdometry):
@@ -88,7 +88,7 @@ class SequentialVisualOdometry(ISequentialVisualOdometry):
                 pts1, pts2, cameraMatrix=K, method=cv2.RANSAC, prob=0.999, threshold=1.0
             )
         except Exception as e:
-            logger.error(f"Error finding essential matrix: {e}")
+            logger.error("essential_matrix_failed", error=str(e))
             return None
 
         if E is None or E.shape != (3, 3):
@@ -98,14 +98,14 @@ class SequentialVisualOdometry(ISequentialVisualOdometry):
         inlier_count = np.sum(inliers_mask)
 
         if inlier_count < inlier_threshold:
-            logger.warning(f"Insufficient inliers: {inlier_count} < {inlier_threshold}")
+            logger.warning("insufficient_inliers", n_inliers=int(inlier_count), threshold=inlier_threshold)
             return None
 
         # Recover pose
         try:
             _, R, t, mask = cv2.recoverPose(E, pts1, pts2, cameraMatrix=K, mask=inliers)
         except Exception as e:
-            logger.error(f"Error recovering pose: {e}")
+            logger.error("recover_pose_failed", error=str(e))
             return None
 
         return Motion(
@@ -224,7 +224,7 @@ class ORBVisualOdometry(ISequentialVisualOdometry):
         try:
             E, inliers = cv2.findEssentialMat(pts1, pts2, cameraMatrix=K, method=cv2.RANSAC, prob=0.999, threshold=1.0)
         except Exception as exc:
-            logger.warning("ORB findEssentialMat failed: %s", exc)
+            logger.warning("orb_essential_matrix_failed", error=str(exc))
             return None
         if E is None or E.shape != (3, 3) or inliers is None:
             return None
@@ -235,7 +235,7 @@ class ORBVisualOdometry(ISequentialVisualOdometry):
         try:
             _, R, t, mask = cv2.recoverPose(E, pts1, pts2, cameraMatrix=K, mask=inliers)
         except Exception as exc:
-            logger.warning("ORB recoverPose failed: %s", exc)
+            logger.warning("orb_recover_pose_failed", error=str(exc))
             return None
         return Motion(translation=t.flatten(), rotation=R, inliers=inlier_mask, inlier_count=inlier_count)
 
diff --git a/src/gps_denied/core/chunk_manager.py b/src/gps_denied/core/chunk_manager.py
index 488d839..9634b59 100644
--- a/src/gps_denied/core/chunk_manager.py
+++ b/src/gps_denied/core/chunk_manager.py
@@ -1,14 +1,15 @@
 """Route Chunk Manager (Component F12)."""
 
-import logging
 import uuid
 from typing import Dict, List, Optional, Protocol, runtime_checkable
 
+import structlog
+
 from gps_denied.core.graph import IFactorGraphOptimizer
 from gps_denied.schemas.chunk import ChunkHandle, ChunkStatus
 from gps_denied.schemas.metric import Sim3Transform
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 @runtime_checkable
@@ -67,7 +68,7 @@ class RouteChunkManager(IRouteChunkManager):
         )
         self._chunks[flight_id][chunk_id] = handle
 
-        logger.info(f"Created new chunk {chunk_id} starting at frame {start_frame_id}")
+        logger.info("chunk_created", chunk_id=chunk_id, start_frame_id=start_frame_id)
         return handle
 
     def get_active_chunk(self, flight_id: str) -> Optional[ChunkHandle]:
@@ -123,7 +124,7 @@ class RouteChunkManager(IRouteChunkManager):
             new_chunk.matching_status = ChunkStatus.MERGED
             new_chunk.is_active = False
 
-            logger.info(f"Merged chunk {new_chunk_id} into {main_chunk_id}")
+            logger.info("chunks_merged", new_chunk_id=new_chunk_id, main_chunk_id=main_chunk_id)
             return True
 
         return False
diff --git a/src/gps_denied/core/eskf.py b/src/gps_denied/core/eskf.py
index 983ab84..7ecb61a 100644
--- a/src/gps_denied/core/eskf.py
+++ b/src/gps_denied/core/eskf.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-import logging
 from typing import TYPE_CHECKING
 
 import numpy as np
+import structlog
 
 from gps_denied.schemas import GPSPoint
 from gps_denied.schemas.eskf import (
@@ -18,7 +18,7 @@ from gps_denied.schemas.eskf import (
 if TYPE_CHECKING:
     from gps_denied.core.coordinates import CoordinateTransformer
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 # ---------------------------------------------------------------------------
@@ -171,7 +171,7 @@ class ESKF:
             return
         dt = imu.timestamp - self._last_timestamp
         if dt <= 0 or dt > 1.0:
-            logger.debug("Skipping IMU prediction: dt=%.4f", dt)
+            logger.debug("imu_prediction_skipped", dt=round(dt, 4))
             return
 
         cfg = self.config
@@ -279,8 +279,9 @@ class ESKF:
         # Mahalanobis outlier gate
         mahal_sq = float(z @ S_inv @ z)
         if mahal_sq > self.config.mahalanobis_threshold:
-            logger.warning("Satellite outlier rejected: Mahalanobis² %.1f > %.1f",
-                          mahal_sq, self.config.mahalanobis_threshold)
+            logger.warning("satellite_outlier_rejected",
+                       mahalanobis_sq=round(mahal_sq, 1),
+                       threshold=self.config.mahalanobis_threshold)
             return z
 
         K = self._P @ H_sat.T @ S_inv
diff --git a/src/gps_denied/core/factor_graph.py b/src/gps_denied/core/factor_graph.py
index 2f0725c..6188a15 100644
--- a/src/gps_denied/core/factor_graph.py
+++ b/src/gps_denied/core/factor_graph.py
@@ -1,10 +1,10 @@
 """Factor Graph Optimizer (Component F10)."""
 
-import logging
 from datetime import datetime, timezone
 from typing import Dict, Protocol, runtime_checkable
 
 import numpy as np
+import structlog
 
 try:
     import gtsam
@@ -17,7 +17,7 @@ from gps_denied.schemas.graph import FactorGraphConfig, OptimizationResult, Pose
 from gps_denied.schemas.metric import Sim3Transform
 from gps_denied.schemas.vo import RelativePose
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 @runtime_checkable
@@ -142,7 +142,7 @@ class FactorGraphOptimizer(IFactorGraphOptimizer):
                         new_t = gtsam.Point3(float(t[0]), float(t[1]), float(t[2]))
                     state["initial"].insert(key_j, gtsam.Pose3(gtsam.Rot3(), new_t))
             except Exception as exc:
-                logger.debug("GTSAM add_relative_factor failed: %s", exc)
+                logger.debug("gtsam_add_relative_factor_failed", error=str(exc))
 
         return True
 
@@ -181,7 +181,7 @@ class FactorGraphOptimizer(IFactorGraphOptimizer):
                 if not state["initial"].exists(key):
                     state["initial"].insert(key, prior)
             except Exception as exc:
-                logger.debug("GTSAM add_absolute_factor failed: %s", exc)
+                logger.debug("gtsam_add_absolute_factor_failed", error=str(exc))
 
         return True
 
@@ -219,7 +219,7 @@ class FactorGraphOptimizer(IFactorGraphOptimizer):
                 state["graph"] = gtsam.NonlinearFactorGraph()
                 state["initial"] = gtsam.Values()
             except Exception as exc:
-                logger.warning("GTSAM ISAM2 update failed: %s", exc)
+                logger.warning("gtsam_isam2_update_failed", error=str(exc))
 
         state["dirty"] = False
         return OptimizationResult(
diff --git a/src/gps_denied/core/recovery.py b/src/gps_denied/core/recovery.py
index 436f3d2..92cbb93 100644
--- a/src/gps_denied/core/recovery.py
+++ b/src/gps_denied/core/recovery.py
@@ -1,16 +1,16 @@
 """Failure Recovery Coordinator (Component F11)."""
 
-import logging
 from typing import List, Protocol, runtime_checkable
 
 import numpy as np
+import structlog
 
 from gps_denied.core.chunk_manager import IRouteChunkManager
 from gps_denied.core.gpr import IGlobalPlaceRecognition
 from gps_denied.core.metric import IMetricRefinement
 from gps_denied.schemas.chunk import ChunkStatus
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 @runtime_checkable
@@ -37,7 +37,7 @@ class FailureRecoveryCoordinator(IFailureRecoveryCoordinator):
 
     def handle_tracking_lost(self, flight_id: str, current_frame_id: int) -> bool:
         """Called when F07 fails to find sequential matches."""
-        logger.warning(f"Tracking lost for flight {flight_id} at frame {current_frame_id}")
+        logger.warning("tracking_lost", flight_id=flight_id, current_frame_id=current_frame_id)
 
         # Create a new active chunk to record new relative frames independently
         self.chunk_manager.create_new_chunk(flight_id, current_frame_id)
diff --git a/src/gps_denied/obs/logging_config.py b/src/gps_denied/obs/logging_config.py
new file mode 100644
index 0000000..70a20c5
--- /dev/null
+++ b/src/gps_denied/obs/logging_config.py
@@ -0,0 +1,67 @@
+"""structlog configuration. Call ``configure_logging`` once at app boot.
+
+Per Phase 2 / OBS-01: hot path uses structlog with ``correlation_id`` (= frame_id)
+bound at frame entry. Non-hot-path code keeps stdlib ``logging`` until Phase 6
+(api/, db/, scripts/, composition.py at startup, core/models.py engine load).
+The stdlib bridge below lets stdlib records flow through the same renderer.
+"""
+from __future__ import annotations
+
+import logging
+from typing import Literal
+
+import orjson
+import structlog
+
+_Env = Literal["jetson", "x86_dev", "ci", "sitl"]
+
+_configured = False
+
+
+def configure_logging(env: _Env, level: int = logging.INFO) -> None:
+    """Configure structlog ONCE at app boot. Idempotent — repeat calls no-op.
+
+    Args:
+        env: Deployment environment. Controls renderer:
+             - ``x86_dev``       -> pretty console renderer
+             - ``jetson|ci|sitl`` -> JSON renderer (orjson) + bytes logger factory
+        level: Stdlib log level threshold. ``filtering_bound_logger`` short-circuits
+               sub-level calls in ~50-100 ns. Keep at INFO in production.
+    """
+    global _configured
+    if _configured:
+        return
+
+    shared_processors: list = [
+        # MUST be first — pulls bound frame_id into every record.
+        structlog.contextvars.merge_contextvars,
+        structlog.processors.add_log_level,
+        structlog.processors.TimeStamper(fmt="iso", utc=True),
+        structlog.processors.format_exc_info,
+    ]
+
+    if env == "x86_dev":
+        processors = [*shared_processors, structlog.dev.ConsoleRenderer()]
+        logger_factory = structlog.PrintLoggerFactory()
+    else:
+        # jetson | ci | sitl — JSON to bytes via orjson; fastest path on hot loop.
+        processors = [
+            *shared_processors,
+            structlog.processors.JSONRenderer(serializer=orjson.dumps),
+        ]
+        logger_factory = structlog.BytesLoggerFactory()
+
+    structlog.configure(
+        processors=processors,
+        wrapper_class=structlog.make_filtering_bound_logger(level),
+        logger_factory=logger_factory,
+        cache_logger_on_first_use=True,
+    )
+
+    # Bridge stdlib logging: api/, db/, scripts/, composition.py, core/models.py
+    # (Phase 6 ports these to structlog directly). Until then, their records share
+    # the same level threshold; format passthrough is via "%(message)s" because the
+    # structlog renderer above is the actual output sink.
+    logging.basicConfig(level=level, format="%(message)s")
+
+    _configured = True
diff --git a/src/gps_denied/pipeline/composition.py b/src/gps_denied/pipeline/composition.py
index 2e73a1a..263df59 100644
--- a/src/gps_denied/pipeline/composition.py
+++ b/src/gps_denied/pipeline/composition.py
@@ -17,6 +17,8 @@ from __future__ import annotations
 import logging
 from typing import Optional
 
+from gps_denied.obs import configure_logging
+
 logger = logging.getLogger(__name__)
 
 
@@ -49,6 +51,10 @@ def build_pipeline(
     FlightProcessor
         Fully wired processor with all components attached.
     """
+    # OBS-01: configure structlog idempotently so tests / scripts calling
+    # build_pipeline directly (without app.py lifespan) still get logging configured.
+    configure_logging(env=env)
+
     # Lazy imports to avoid circular import chains at module load time.
     from gps_denied.components.gpr.faiss_gpr import GlobalPlaceRecognition
     from gps_denied.components.mavlink_io.pymavlink_bridge import MAVLinkBridge
diff --git a/src/gps_denied/pipeline/orchestrator.py b/src/gps_denied/pipeline/orchestrator.py
index 0038996..09d31ac 100644
--- a/src/gps_denied/pipeline/orchestrator.py
+++ b/src/gps_denied/pipeline/orchestrator.py
@@ -7,12 +7,13 @@ State Machine: NORMAL → LOST → RECOVERY → NORMAL.
 from __future__ import annotations
 
 import asyncio
-import logging
 import time
 from enum import Enum
 from typing import Optional
 
 import numpy as np
+import structlog
+from structlog.contextvars import bind_contextvars, clear_contextvars
 
 from gps_denied.core.eskf import ESKF
 from gps_denied.pipeline.image_input import ImageInputPipeline
@@ -36,7 +37,7 @@ from gps_denied.schemas.flight import (
     Waypoint,
 )
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger(__name__)
 
 
 # ---------------------------------------------------------------------------
@@ -178,6 +179,23 @@ class FlightProcessor:
         PIPE-05: ImageRotationManager initialised on first frame
         PIPE-07: ESKF confidence → MAVLink fix_type via bridge.update_state
         """
+        # OBS-01: bind correlation_id=frame_id for the duration of this frame.
+        # All hot-path log calls (in this file + the 9 component files) auto-include
+        # frame_id and flight_id via structlog.contextvars.merge_contextvars.
+        clear_contextvars()
+        bind_contextvars(correlation_id=frame_id, flight_id=flight_id)
+        try:
+            return await self._process_frame_inner(flight_id, frame_id, image)
+        finally:
+            clear_contextvars()
+
+    async def _process_frame_inner(
+        self,
+        flight_id: str,
+        frame_id: int,
+        image,
+    ):
+        """Inner frame processing — called with correlation_id already bound."""
         result = FrameResult(frame_id)
         state = self._flight_states.get(flight_id, TrackingState.NORMAL)
         eskf = self._eskf.get(flight_id)
@@ -187,6 +205,8 @@ class FlightProcessor:
             resolution_width=640, resolution_height=480,
         )
 
+        logger.info("frame_started", state=state.value)
+
         # ---- PIPE-05: Initialise heading tracking on first frame ----
         if self._rotation and frame_id == 0:
             self._rotation.requires_rotation_sweep(flight_id)  # seeds HeadingHistory
@@ -214,7 +234,7 @@ class FlightProcessor:
                         dt_vo = max(0.01, now - (eskf.last_timestamp or now))
                         eskf.update_vo(rel_pose.translation, dt_vo)
             except Exception as exc:
-                logger.warning("VO failed for frame %d: %s", frame_id, exc)
+                logger.warning("vo_failed", error=str(exc))
 
         # Store current image for next frame
         self._prev_images[flight_id] = image
@@ -229,7 +249,7 @@ class FlightProcessor:
         if state == TrackingState.NORMAL:
             if not vo_ok and frame_id > 0:
                 state = TrackingState.LOST
-                logger.info("Flight %s → LOST at frame %d", flight_id, frame_id)
+                logger.info("flight_state_change", new_state="LOST")
                 if self._recovery:
                     self._recovery.handle_tracking_lost(flight_id, frame_id)
 
@@ -249,7 +269,7 @@ class FlightProcessor:
                 result.alignment_success = True
                 # PIPE-04: Reset failure count on successful recovery
                 self._failure_counts[flight_id] = 0
-                logger.info("Flight %s recovered → NORMAL at frame %d", flight_id, frame_id)
+                logger.info("flight_state_change", new_state="NORMAL", source="recovery")
 
         # ---- 3. Satellite position fix (PIPE-01/02) ----
         if state == TrackingState.NORMAL and self._metric:
@@ -274,7 +294,7 @@ class FlightProcessor:
                         if tile_result:
                             sat_tile, tile_bounds = tile_result
                     except Exception as exc:
-                        logger.debug("Satellite tile fetch failed: %s", exc)
+                        logger.debug("satellite_tile_fetch_failed", error=str(exc))
 
             # Fallback: GPR candidate tile (mock image, real bounds)
             if sat_tile is None and self._gpr:
@@ -284,7 +304,7 @@ class FlightProcessor:
                         sat_tile = np.zeros((256, 256, 3), dtype=np.uint8)
                         tile_bounds = candidates[0].bounds
                 except Exception as exc:
-                    logger.debug("GPR tile fallback failed: %s", exc)
+                    logger.debug("gpr_tile_fallback_failed", error=str(exc))
 
             if sat_tile is not None and tile_bounds is not None:
                 try:
@@ -310,16 +330,17 @@ class FlightProcessor:
                                 noise_m = 5.0 + 15.0 * (1.0 - float(align.confidence))
                                 eskf.update_satellite(pos_enu, noise_m)
                             except Exception as exc:
-                                logger.debug("ESKF satellite update failed: %s", exc)
+                                logger.debug("eskf_satellite_update_failed", error=str(exc))
                 except Exception as exc:
-                    logger.warning("Metric alignment failed at frame %d: %s", frame_id, exc)
+                    logger.warning("metric_alignment_failed", error=str(exc))
 
         # ---- 4. Graph optimization (incremental) ----
         if self._graph:
             opt_result = self._graph.optimize(flight_id, iterations=5)
             logger.debug(
-                "Optimization: converged=%s, error=%.4f",
-                opt_result.converged, opt_result.final_error,
+                "graph_optimized",
+                converged=opt_result.converged,
+                error=round(opt_result.final_error, 4),
             )
 
         # ---- PIPE-07: Push ESKF state → MAVLink GPS_INPUT ----
@@ -329,11 +350,12 @@ class FlightProcessor:
                 alt = self._altitudes.get(flight_id, 100.0)
                 self._mavlink.update_state(eskf_state, altitude_m=alt)
             except Exception as exc:
-                logger.debug("MAVLink state push failed: %s", exc)
+                logger.debug("mavlink_state_push_failed", error=str(exc))
 
         # ---- 5. Publish via SSE ----
         result.tracking_state = state
         self._flight_states[flight_id] = state
+        logger.info("frame_complete", tracking_state=state.value, alignment=result.alignment_success)
         await self._publish_frame_result(flight_id, result)
         return result
 
@@ -393,7 +415,7 @@ class FlightProcessor:
             try:
                 asyncio.create_task(self._mavlink.start(req.start_gps))
             except Exception as exc:
-                logger.warning("MAVLink bridge start failed: %s", exc)
+                logger.warning("mavlink_bridge_start_failed", error=str(exc))
 
         return FlightResponse(
             flight_id=flight.id,
@@ -532,9 +554,9 @@ class FlightProcessor:
                 alt = self._altitudes.get(flight_id, 100.0)
                 eskf.update_satellite(np.array([e, n, alt]), noise_meters=500.0)
                 self._failure_counts[flight_id] = 0
-                logger.info("User fix applied for %s: %s", flight_id, req.satellite_gps)
+                logger.info("user_fix_applied", flight_id=flight_id, gps=str(req.satellite_gps))
             except Exception as exc:
-                logger.warning("User fix ESKF injection failed: %s", exc)
+                logger.warning("user_fix_eskf_failed", error=str(exc))
 
         return UserFixResponse(
             accepted=True, processing_resumed=True, message="Fix applied."
@@ -580,7 +602,7 @@ class FlightProcessor:
                     quaternion=quat,
                 )
             except Exception as exc:
-                logger.debug("pixel_to_gps failed: %s", exc)
+                logger.debug("pixel_to_gps_failed", error=str(exc))
 
         # Fallback: return ESKF position projected to ground (no pixel shift)
         if gps is None and eskf:
diff --git a/tests/conftest.py b/tests/conftest.py
index e237200..1899cdb 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -9,6 +9,96 @@ from gps_denied.core.coordinates import CoordinateTransformer
 from gps_denied.core.models import ModelManager
 from gps_denied.schemas import CameraParameters, GPSPoint
 
+# ---------------------------------------------------------------
+# Phase 2 / TEST-03: AC traceability plugin
+#
+# Registers categorical markers (defensive — pyproject.toml is primary), validates
+# @pytest.mark.ac() arguments against the canonical AC-ID regex at collection time,
+# and (when --ac-dump=<path> is supplied) writes a {ac_id: [test_nodeid, ...]} JSON
+# at session end for `scripts/gen_ac_traceability.py` to consume.
+#
+# See RESEARCH.md §2.1 for the canonical implementation and rationale.
+# ---------------------------------------------------------------
+import json
+import re
+from collections import defaultdict
+from pathlib import Path
+
+_AC_ID_RE = re.compile(r"^AC-(?:\d+\.\d+[a-z]?|NEW-\d+)$")
+
+
+def pytest_configure(config):
+    """Defensive marker registration. Primary registration lives in pyproject.toml,
+    but doing it here too means a future maintainer who drops the pyproject markers
+    list does not silently break --strict-markers."""
+    for line in (
+        "unit: pure-math or single-class test; no I/O",
+        "integration: cross-subsystem test; in-memory SQLite / ASGI / full wiring",
+        "blackbox: validates external contract without a live producer",
+        "sitl: requires ARDUPILOT_SITL_HOST — nightly only",
+        "e2e: full-pipeline run against a real dataset — nightly only",
+        "ac(ac_id): link test to one or more Acceptance Criteria (e.g. AC-1.1, AC-NEW-3)",
+    ):
+        config.addinivalue_line("markers", line)
+
+
+def pytest_addoption(parser):
+    parser.addoption(
+        "--ac-dump",
+        action="store",
+        default=None,
+        help="Path to write the {ac_id: [test_nodeid, ...]} JSON at session end. "
+             "Consumed by scripts/gen_ac_traceability.py.",
+    )
+
+
+def pytest_collection_modifyitems(config, items):
+    """Validate @pytest.mark.ac(...) arguments against the canonical AC-ID regex.
+
+    Fail collection (rather than emit a runtime error) so AC-ID typos surface immediately.
+    The traceability script's --check mode catches forward orphans (AC without test);
+    this hook catches backward orphans (test references non-existent AC) by enforcing
+    the syntactic AC-ID shape. Semantic existence (AC ID is declared in the AC doc) is
+    enforced by the script in Plan 02-04.
+    """
+    errors = []
+    for item in items:
+        for mark in item.iter_markers(name="ac"):
+            if not mark.args:
+                errors.append(
+                    f"{item.nodeid}: @pytest.mark.ac() requires at least one AC ID arg"
+                )
+                continue
+            for arg in mark.args:
+                if not isinstance(arg, str) or not _AC_ID_RE.match(arg):
+                    errors.append(
+                        f"{item.nodeid}: @pytest.mark.ac({arg!r}) — must match "
+                        f"AC-X.Y or AC-NEW-N (e.g. 'AC-1.1', 'AC-NEW-3')"
+                    )
+    if errors:
+        raise pytest.UsageError(
+            "AC marker validation failed:\n  " + "\n  ".join(errors)
+        )
+
+
+def pytest_sessionfinish(session, exitstatus):
+    """Dump {ac_id: [test_nodeid, ...]} to --ac-dump path if supplied.
+
+    Runs even when pytest is invoked with --collect-only (session.items is populated
+    before tests execute), so scripts/gen_ac_traceability.py can dump in ~seconds on a
+    full suite.
+    """
+    dump_path = session.config.getoption("--ac-dump", default=None)
+    if not dump_path:
+        return
+    mapping: dict[str, list[str]] = defaultdict(list)
+    for item in session.items:
+        for mark in item.iter_markers(name="ac"):
+            for ac_id in mark.args:
+                mapping[ac_id].append(item.nodeid)
+    Path(dump_path).write_text(json.dumps(dict(sorted(mapping.items())), indent=2))
+
+
 # ---------------------------------------------------------------
 # Common constants
 # ---------------------------------------------------------------