[AZ-596] Batch 76: fc_proxy_runtime driver (FDR-replay mode)

Add `runner/helpers/fc_proxy_runtime.py` wrapping the existing
`BlackoutSpoofProxy` (AZ-406) with a scenario-facing `drive_fc_proxy`
entry point. FDR-replay mode only: loads `schedule.json`, optionally
activates the proxy against a caller clock for alignment verification,
and writes a `proxy_drive_report.json` audit record into
`${E2E_SITL_REPLAY_DIR}` for downstream evaluators.

Replaces the local `_drive_fc_proxy` stub in FT-N-04. Adds 3
@property accessors on `BlackoutSpoofProxy` so the wrapper does not
reach into private attributes. +11 unit tests (608 total, up from
596). Live-mode router wiring remains out of scope (future ticket).

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

_docs/02_tasks/done/AZ-596_fc_proxy_runtime.md

@@ -0,0 +1,91 @@
+# fc_proxy_runtime driver (FDR-replay mode) for FT-N-04
+
+**Task**: AZ-596_fc_proxy_runtime
+**Name**: Implement runtime driver wrapping BlackoutSpoofProxy + replace FT-N-04 stub
+**Description**: Add `runner/helpers/fc_proxy_runtime.py` with `drive_fc_proxy(schedule_path, *, now_ms_provider=None)` that loads the blackout-spoof schedule via the existing `fixtures/injectors/fc_proxy.BlackoutSpoofProxy`, returns a `ProxyDriveReport`, and (when `E2E_SITL_REPLAY_DIR` is set) writes `proxy_drive_report.json` for downstream evaluators. Replace the local `_drive_fc_proxy` `NotImplementedError` stub in FT-N-04 with the new helper. FDR-replay mode only — live MAVLink router wiring is out of scope.
+**Complexity**: 2 points
+**Dependencies**: AZ-406 (`fixtures/injectors/fc_proxy.BlackoutSpoofProxy`), AZ-595 (`sitl_observer.replay_dir`)
+**Component**: Blackbox Tests / Test Infrastructure (epic AZ-262)
+**Tracker**: AZ-596
+**Epic**: AZ-262 (E-BBT)
+
+## Problem
+
+FT-N-04 (`test_ft_n_04_blackout_spoof`) calls a local stub:
+
+```python
+def _drive_fc_proxy(schedule_path: Path) -> None:
+    raise NotImplementedError(
+        "FC-inbound spoof proxy driver is owned by AZ-441 / runner.helpers.fc_proxy_runtime"
+    )
+```
+
+The `BlackoutSpoofProxy` itself was implemented under AZ-406's injector
+module — fully unit-tested, accepts a `now_ms_provider`, exposes
+`activate(...)` + `process_inbound_message(...)`. What's missing is the
+**runtime driver** that the scenario calls to wrap the proxy: load the
+schedule, activate it, optionally record what happened so downstream
+evaluators (`sitl_observer.read_gps_health_samples` /
+`read_consistency_check_events`) can correlate.
+
+In **FDR-replay mode** (the AZ-595 strategy), the actual FC inbound
+transport is not real — the SITL replay fixture builder pre-bakes the
+expected spoofed-GPS-rejected events into the FDR JSON files. So the
+runtime driver doesn't need to plumb into a live MAVLink router. It
+just needs to (a) validate the schedule loads correctly, (b) optionally
+align with the harness clock, and (c) write a small audit report into
+`${E2E_SITL_REPLAY_DIR}` so evaluators can verify the schedule actually
+ran.
+
+Live-mode driving (real MAVLink router + actual FC inbound) is out of
+scope for this ticket and is a separate live-mode infrastructure task.
+
+## Surfaces
+
+* `drive_fc_proxy(schedule_path: Path, *, now_ms_provider: NowMsProvider | None = None, replay_dir: Path | None = None) -> ProxyDriveReport`
+  * Loads the schedule via `BlackoutSpoofProxy.from_schedule_file(schedule_path)`.
+  * If `now_ms_provider` is supplied: activates the proxy and reads
+    `alignment_err_ms` from the activation report.
+  * If `now_ms_provider` is None: emits `ProxyDriveReport` with
+    `alignment_err_ms=0` and `was_replay_mode=True`.
+  * If `replay_dir` is supplied (or resolved from `E2E_SITL_REPLAY_DIR`):
+    writes `proxy_drive_report.json` into that directory.
+* `ProxyDriveReport` (frozen dataclass): `schedule_path: Path`,
+  `window_start_ms: int`, `window_end_ms: int`, `spoof_frame_count: int`,
+  `alignment_err_ms: int`, `was_replay_mode: bool`.
+
+## Acceptance Criteria
+
+**AC-1**: `drive_fc_proxy(schedule_path)` loads the schedule via
+`BlackoutSpoofProxy.from_schedule_file`. Missing `schedule_path` →
+`FileNotFoundError` (inherited from `BlackoutSpoofProxy`). Malformed
+JSON → `ValueError` with the file path.
+
+**AC-2**: When `now_ms_provider` is supplied, the driver activates the
+proxy and records `alignment_err_ms` on the report. When unsupplied,
+the report fills `alignment_err_ms=0` and `was_replay_mode=True`.
+
+**AC-3**: When `replay_dir` is supplied (or `E2E_SITL_REPLAY_DIR` env
+var is set), the driver writes `proxy_drive_report.json` into that
+directory. When neither is supplied, no file is written.
+
+**AC-4**: ≥5 unit tests covering: happy path, missing schedule path,
+malformed schedule JSON, replay-mode JSON write, no-write when env var
+unset, alignment-error path with injected clock.
+
+**AC-5**: Full e2e unit-test suite passes (regression gate).
+
+## Out of Scope
+
+* Live MAVLink router wiring + docker-compose orchestration.
+* Other per-scenario `_resolve_*` / `_drive_*` stubs (`_resolve_frame_sink`,
+  `_resolve_fc_inbound_emitter`, `_resolve_outage_injection_frames`,
+  `_resolve_gt_per_frame`, `_drive_imu_replay`, `_resolve_frame_period_ms`)
+  — each gets its own follow-up ticket.
+
+## Files Touched
+
+* `e2e/runner/helpers/fc_proxy_runtime.py` (new)
+* `e2e/_unit_tests/helpers/test_fc_proxy_runtime.py` (new)
+* `e2e/tests/negative/test_ft_n_04_blackout_spoof.py` (replace local stub)
+* `e2e/_unit_tests/test_directory_layout.py` (register new module)

_docs/03_implementation/batch_76_report.md

@@ -0,0 +1,91 @@
+# Batch 76 Report — fc_proxy_runtime driver (cycle 1, batch 10 of test phase)
+
+**Batch**: 76
+**Date**: 2026-05-17
+**Context**: Test implementation (greenfield Step 10 — Implement Tests)
+**Tasks**: AZ-596 (2 cp) — 1 task (fc_proxy_runtime driver, FDR-replay mode)
+**Cycle**: 1
+**Verdict**: COMPLETE — PASS (self-reviewed; see `reviews/batch_76_review.md`)
+
+## Summary
+
+Final piece of the harness-stubs arc that started in batch 74. The
+FT-N-04 (`test_ft_n_04_blackout_spoof`) scenario called a local
+`_drive_fc_proxy` stub that raised
+`NotImplementedError("FC-inbound spoof proxy driver is owned by
+runner.helpers.fc_proxy_runtime")`. That module didn't exist. The
+`BlackoutSpoofProxy` state machine (load schedule, activate, replace
+inbound GPS frames inside the window) was already fully implemented
+under AZ-406 in `fixtures/injectors/fc_proxy.py` — what was missing
+was the scenario-facing wrapper.
+
+This batch adds `runner/helpers/fc_proxy_runtime.py` (one function +
+one dataclass) using the same **FDR-replay strategy** as AZ-595:
+the runtime driver does not plumb into a live MAVLink router. It
+loads the schedule, optionally activates the proxy against a
+caller-supplied clock, and writes a small audit JSON
+(`proxy_drive_report.json`) into `${E2E_SITL_REPLAY_DIR}` so the
+downstream FDR evaluators can correlate. Live-mode driving (real
+router + real FC) is explicitly a separate live-mode infrastructure
+ticket.
+
+### AZ-596 — fc_proxy_runtime driver (2 cp)
+
+* **`runner/helpers/fc_proxy_runtime.py`** —
+  `drive_fc_proxy(schedule_path, *, now_ms_provider=None, replay_dir=None)`:
+  * Loads the schedule via
+    `BlackoutSpoofProxy.from_schedule_file(schedule_path)`.
+  * Wraps `json.JSONDecodeError` as `ValueError` with a file pointer
+    (consistent with the rest of `e2e/runner/helpers/`).
+  * When `now_ms_provider` is supplied, activates the proxy and
+    records the resulting `alignment_err_ms`. When absent, sets
+    `was_replay_mode=True`.
+  * Resolves the write directory in this order: explicit
+    `replay_dir` argument > `${E2E_SITL_REPLAY_DIR}` env var > no
+    write. The chosen directory is created if missing.
+  * Returns `ProxyDriveReport` (frozen dataclass with
+    `schedule_path, window_start_ms, window_end_ms,
+    spoof_frame_count, alignment_err_ms, was_replay_mode`).
+* **`fixtures/injectors/fc_proxy.py`** — added three additive
+  `@property` accessors (`window_start_ms`, `window_end_ms`,
+  `spoof_frame_count`) so the runtime wrapper does NOT reach into
+  private attributes. Existing callers unaffected.
+* **FT-N-04 scenario** — local `_drive_fc_proxy` stub replaced
+  with `from runner.helpers.fc_proxy_runtime import drive_fc_proxy;
+  drive_fc_proxy(schedule_path)`. The scenario's b75
+  `sitl_replay_ready` skip gate continues to govern when this
+  code path actually runs.
+* **Directory layout test** — registered the new
+  `runner/helpers/fc_proxy_runtime.py` path.
+
+## Out of scope (deferred)
+
+* **Live MAVLink router + FC inbound transport** — the runtime
+  driver currently does not wire `proxy.process_inbound_message`
+  into a real router. A live-mode follow-up ticket will own the
+  docker-compose-bound MAVLink router that plumbs in the
+  per-message replace.
+* **Other per-scenario `_resolve_*` / `_drive_*` stubs**
+  (`_resolve_frame_sink`, `_resolve_fc_inbound_emitter`,
+  `_resolve_outage_injection_frames`, `_resolve_gt_per_frame`,
+  `_drive_imu_replay`, `_resolve_frame_period_ms`) — each will get
+  its own follow-up ticket. They remain `NotImplementedError`
+  stubs in their respective scenario files; the `sitl_replay_ready`
+  skip gate ensures they're never reached in unit-test mode.
+
+## Test Results
+
+* New unit tests: **11** (3 schedule load/error, 2 activation, 6
+  replay-dir write).
+* Full `e2e/_unit_tests` suite: **608 passed in 124 s** (previous
+  cumulative: 596 → +12 net = +11 new fc_proxy_runtime tests + 1
+  new directory-layout parametrize entry).
+* No new linter errors.
+
+## State
+
+* Spec moved: `_docs/02_tasks/todo/AZ-596_fc_proxy_runtime.md`
+  → `_docs/02_tasks/done/`.
+* `_docs/_autodev_state.md` advanced to `last_completed_batch: 76`.
+* `last_cumulative_review` remains `batches_73-75`; next K=3
+  cumulative review fires at the end of batch 78.

_docs/03_implementation/reviews/batch_76_review.md

@@ -0,0 +1,142 @@
+# Code Review Report
+
+**Batch**: 76 — AZ-596 (fc_proxy_runtime driver, FDR-replay mode)
+**Date**: 2026-05-17
+**Verdict**: PASS
+
+## Findings
+
+(none)
+
+## Findings Sweep
+
+### Phase 1 — Context Loading
+
+Read the AZ-596 task spec, the existing
+`fixtures/injectors/fc_proxy.py` (`BlackoutSpoofProxy`,
+`SpoofGpsRecord`, `ProxyAlignmentReport`, lifecycle methods), the
+FT-N-04 scenario's local `_drive_fc_proxy` stub and the surrounding
+call site, and the AZ-595 `sitl_observer` env-var pattern
+(`E2E_SITL_REPLAY_DIR` resolution via `replay_dir()`). Verified that
+`BlackoutSpoofProxy.from_schedule_file` already raises
+`FileNotFoundError` for missing input and `json.JSONDecodeError` for
+malformed JSON, so the runtime wrapper only needs to (a) convert
+`JSONDecodeError → ValueError` with a file pointer for symmetry with
+the rest of the helper layer and (b) project the proxy state into a
+small audit dataclass.
+
+### Phase 2 — Spec Compliance
+
+| AC | Coverage | Status |
+|----|----------|--------|
+| AC-1 (`drive_fc_proxy` loads schedule via `BlackoutSpoofProxy.from_schedule_file`; missing → `FileNotFoundError`; malformed → `ValueError`) | `test_missing_schedule_raises_file_not_found`, `test_malformed_json_raises_value_error`, `test_happy_path_returns_well_formed_report` | Covered |
+| AC-2 (`now_ms_provider` supplied → proxy activated, `alignment_err_ms` recorded; absent → `alignment_err_ms=0`, `was_replay_mode=True`) | `test_now_ms_provider_activates_proxy_and_reports_alignment`, `test_now_ms_provider_with_replay_mode_false_distinguishes_from_default`, plus the `was_replay_mode is True` assertion in the happy-path test | Covered |
+| AC-3 (`replay_dir` supplied OR `E2E_SITL_REPLAY_DIR` set → `proxy_drive_report.json` written; neither → no write) | `test_writes_report_when_replay_dir_supplied`, `test_writes_report_when_env_var_set`, `test_explicit_replay_dir_overrides_env_var`, `test_no_file_written_when_neither_supplied`, `test_no_file_written_when_env_var_empty`, `test_replay_dir_is_created_when_missing` | Covered |
+| AC-4 (≥5 unit tests covering happy + 3 error/edge + 1 boundary) | 11 tests total (3 schedule-load, 2 activation, 6 replay-dir write paths) | Covered (exceeds floor) |
+| AC-5 (full suite passes) | 608 passed (+12 from 596 baseline; +11 new tests + 1 layout parametrize entry) | Covered |
+
+### Phase 3 — Code Quality
+
+* **Single responsibility**: `drive_fc_proxy` owns three things and
+  three things only — (a) construct a `BlackoutSpoofProxy` from a
+  schedule path, (b) optionally activate it against a caller-supplied
+  clock, (c) project the proxy state into `ProxyDriveReport` and
+  optionally persist it. Each branch is straight-line.
+* **`ProxyDriveReport` is a frozen dataclass** with seven plain fields
+  — no methods, no factories. The dataclass IS the contract; downstream
+  evaluators read it via `asdict` or per-field access.
+* **`_resolve_replay_dir` is the single env-var reader** in this
+  module. It mirrors the equivalent reader in `sitl_observer.replay_dir`
+  (same env var, same "empty string → None" semantics) — the two
+  modules deliberately do not import each other so the dependency
+  surface stays one-way (`fc_proxy_runtime` → `BlackoutSpoofProxy`,
+  `fc_proxy_runtime` → `os.environ`; nothing else).
+* **No suppressed errors**: the one `try`/`except` block converts
+  `json.JSONDecodeError` to a `ValueError` with the offending file
+  path AND preserves the original via `raise … from exc`. No bare
+  `except`, no `2>/dev/null`, no empty `pass`.
+* **Public-accessor addition on `BlackoutSpoofProxy`**: added three
+  `@property` accessors (`window_start_ms`, `window_end_ms`,
+  `spoof_frame_count`) so the runtime driver does NOT reach into
+  private `_window_start_ms` / `_spoof_gps` attributes. The properties
+  are pure, side-effect-free, single-line reads — they purely
+  formalise the existing public read surface that `from_schedule_file`
+  already establishes.
+* **AAA comment discipline**: all 11 new tests use
+  `# Arrange / # Act / # Assert`; sections omitted when not needed.
+* **No code comments narrate code** — module docstring explains the
+  FDR-replay rationale and the live-mode out-of-scope boundary.
+  Per-function docstrings document the parameter contract.
+* **Public boundary**: imports only stdlib (`json`, `os`,
+  `dataclasses`, `pathlib`, `typing`) +
+  `fixtures.injectors.fc_proxy.BlackoutSpoofProxy` (an existing
+  test-side module). Zero `from gps_denied_onboard ...` imports.
+
+### Phase 4 — Security
+
+* **No new credentials, secrets, or network surface**. The driver is
+  pure file I/O over caller-supplied (or env-var-rooted) paths.
+* **`E2E_SITL_REPLAY_DIR`** is read-only (consistent with AZ-595).
+  Written paths use `Path` arithmetic — no string-interpolation into
+  shell, no `eval`, no `subprocess`.
+* **JSON write path** uses `json.dumps(asdict(report))` — no opaque
+  pickle, no untrusted deserialisation of caller input.
+* **`replay_dir.mkdir(parents=True, exist_ok=True)`** silently creates
+  intermediate directories. This is acceptable because the path comes
+  from the test harness's own env var, not from external input.
+
+### Phase 5 — Performance
+
+* O(1) work beyond the upstream `BlackoutSpoofProxy.from_schedule_file`
+  load (which itself is O(N) in the number of spoof frames; the
+  dataclass projection is constant-time using the new properties).
+* No I/O at module-import time.
+* The JSON write path is a single `write_text` call — atomic-enough
+  for the audit-only use case.
+
+### Phase 6 — Cross-Task Consistency
+
+* **Env-var pattern matches AZ-595**: the same `E2E_SITL_REPLAY_DIR`
+  semantics (set → use; unset / empty / whitespace → ignore). A
+  future fixture builder will set the env var once for the whole
+  scenario run, and both `sitl_observer` (reads) + `fc_proxy_runtime`
+  (writes the audit report) consume it from a single source of truth.
+* **`ProxyDriveReport` field names mirror the existing
+  `ProxyAlignmentReport`** in `fc_proxy.py` for `alignment_err_ms`.
+  No name churn for the AC-3 / AC-NEW-3 evaluator that will eventually
+  read it (`blackout_spoof_evaluator` already references
+  `alignment_err_ms` from the proxy's own activation report).
+* **`FileNotFoundError` / `ValueError` discipline matches the rest of
+  `e2e/runner/helpers/`** (per the b73-b75 cumulative review): missing
+  inputs → `FileNotFoundError`, malformed inputs → `ValueError` with a
+  file pointer.
+* **FT-N-04 scenario rewire**: the local `_drive_fc_proxy` stub now
+  imports `runner.helpers.fc_proxy_runtime.drive_fc_proxy` and calls
+  it. The scenario's `sitl_replay_ready` skip gate (added in b75)
+  continues to gate on `E2E_SITL_REPLAY_DIR`; the new helper writes
+  its audit report into that same directory when the gate is open.
+
+### Phase 7 — Architecture Compliance
+
+* **Module placement**: `e2e/runner/helpers/fc_proxy_runtime.py` (new)
+  + `e2e/_unit_tests/helpers/test_fc_proxy_runtime.py` (new). Both
+  registered in `e2e/_unit_tests/test_directory_layout.py`; the
+  layout invariant test still passes.
+* **No `src/gps_denied_onboard` imports** anywhere. Confirmed.
+* **No new top-level dependencies** — stdlib only on the runner side;
+  the test side adds nothing new. `requirements.txt` untouched.
+* **Backwards-compatible**: the `BlackoutSpoofProxy` change is purely
+  additive — three new `@property` accessors. Existing callers
+  (the injector's own self-tests, the FT-N-04 fixture) keep working
+  unchanged.
+
+## Test Results
+
+* New unit tests: **11** (3 schedule load/error, 2 activation, 6
+  replay-dir write).
+* Full `e2e/_unit_tests` suite: **608 passed in 124 s** (previous
+  cumulative: 596 → +12 net = +11 new fc_proxy_runtime tests + 1
+  new directory-layout parametrize entry).
+* No new linter errors (`ReadLints` clean on `fc_proxy_runtime.py`,
+  `test_fc_proxy_runtime.py`, `fc_proxy.py`,
+  `test_ft_n_04_blackout_spoof.py`, `test_directory_layout.py`).

_docs/_autodev_state.md

@@ -12,9 +12,9 @@ sub_step:
 retry_count: 0
 cycle: 1
 tracker: jira
-last_completed_batch: 75
+last_completed_batch: 76
 last_cumulative_review: batches_73-75
-current_batch: 76
+current_batch: 77
 current_batch_tasks: ""
 last_step_outcomes:
   step_8: "Code is testable — no changes needed (testability_assessment.md committed; no list-of-changes, no source edits)"

e2e/_unit_tests/helpers/test_fc_proxy_runtime.py

@@ -0,0 +1,206 @@
+"""Unit tests for `e2e/runner/helpers/fc_proxy_runtime.py` (AZ-596)."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import pytest
+
+from e2e.runner.helpers import fc_proxy_runtime as fpr
+
+
+def _schedule_payload(
+    *,
+    window_start_ms: int = 10_000,
+    window_end_ms: int = 25_000,
+    spoof_frame_count: int = 5,
+) -> dict:
+    """Build a minimally valid `schedule.json` payload that `BlackoutSpoofProxy.from_schedule_file` accepts."""
+    return {
+        "window_start_ms": window_start_ms,
+        "window_end_ms": window_end_ms,
+        "max_alignment_err_ms": 40.0,
+        "spoof_gps": [
+            {
+                "monotonic_ms": window_start_ms + (i * 200),
+                "lat_deg": 50.0 + (i * 0.0001),
+                "lon_deg": 36.2 + (i * 0.0001),
+                "alt_m": 200.0,
+                "fix_type": 3,
+                "hdop": 1.0,
+            }
+            for i in range(spoof_frame_count)
+        ],
+    }
+
+
+def _write_schedule(path: Path, payload: dict) -> None:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(json.dumps(payload))
+
+
+# AC-1: schedule load + error branches
+
+
+def test_missing_schedule_raises_file_not_found(tmp_path: Path):
+    # Assert
+    with pytest.raises(FileNotFoundError, match="schedule.json not found"):
+        fpr.drive_fc_proxy(tmp_path / "nope.json")
+
+
+def test_malformed_json_raises_value_error(tmp_path: Path):
+    # Arrange
+    bad = tmp_path / "schedule.json"
+    bad.write_text("{not valid json")
+
+    # Assert
+    with pytest.raises(ValueError, match="malformed schedule JSON"):
+        fpr.drive_fc_proxy(bad)
+
+
+def test_happy_path_returns_well_formed_report(tmp_path: Path):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload(spoof_frame_count=7))
+
+    # Act
+    report = fpr.drive_fc_proxy(schedule)
+
+    # Assert
+    assert report.schedule_path == str(schedule)
+    assert report.window_start_ms == 10_000
+    assert report.window_end_ms == 25_000
+    assert report.spoof_frame_count == 7
+    assert report.alignment_err_ms == 0
+    assert report.was_replay_mode is True
+
+
+# AC-2: now_ms_provider activation + alignment_err_ms
+
+
+def test_now_ms_provider_activates_proxy_and_reports_alignment(tmp_path: Path):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload(window_start_ms=5_000))
+
+    def clock() -> int:
+        return 5_002  # 2 ms drift from window_start_ms
+
+    # Act
+    report = fpr.drive_fc_proxy(schedule, now_ms_provider=clock)
+
+    # Assert
+    assert report.alignment_err_ms == 0  # `activate(...)` with no first_blackout_ms anchors at `now`
+    assert report.was_replay_mode is False
+
+
+def test_now_ms_provider_with_replay_mode_false_distinguishes_from_default(tmp_path: Path):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload())
+
+    # Act
+    replay_report = fpr.drive_fc_proxy(schedule)
+    live_report = fpr.drive_fc_proxy(schedule, now_ms_provider=lambda: 12_345)
+
+    # Assert
+    assert replay_report.was_replay_mode is True
+    assert live_report.was_replay_mode is False
+
+
+# AC-3: replay_dir / E2E_SITL_REPLAY_DIR JSON write
+
+
+def test_writes_report_when_replay_dir_supplied(tmp_path: Path):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload(spoof_frame_count=3))
+    replay_dir = tmp_path / "replay"
+
+    # Act
+    fpr.drive_fc_proxy(schedule, replay_dir=replay_dir)
+
+    # Assert
+    report_path = replay_dir / "proxy_drive_report.json"
+    assert report_path.is_file()
+    written = json.loads(report_path.read_text())
+    assert written["spoof_frame_count"] == 3
+    assert written["was_replay_mode"] is True
+
+
+def test_writes_report_when_env_var_set(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload())
+    env_dir = tmp_path / "from-env"
+    monkeypatch.setenv("E2E_SITL_REPLAY_DIR", str(env_dir))
+
+    # Act
+    fpr.drive_fc_proxy(schedule)
+
+    # Assert
+    assert (env_dir / "proxy_drive_report.json").is_file()
+
+
+def test_explicit_replay_dir_overrides_env_var(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload())
+    env_dir = tmp_path / "from-env"
+    explicit_dir = tmp_path / "explicit"
+    monkeypatch.setenv("E2E_SITL_REPLAY_DIR", str(env_dir))
+
+    # Act
+    fpr.drive_fc_proxy(schedule, replay_dir=explicit_dir)
+
+    # Assert
+    assert (explicit_dir / "proxy_drive_report.json").is_file()
+    assert not (env_dir / "proxy_drive_report.json").exists()
+
+
+def test_no_file_written_when_neither_supplied(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload())
+    monkeypatch.delenv("E2E_SITL_REPLAY_DIR", raising=False)
+
+    # Act
+    fpr.drive_fc_proxy(schedule)
+
+    # Assert: nothing written next to the schedule (the only writable dir)
+    assert list(tmp_path.iterdir()) == [schedule]
+
+
+def test_no_file_written_when_env_var_empty(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload())
+    monkeypatch.setenv("E2E_SITL_REPLAY_DIR", "   ")
+
+    # Act
+    fpr.drive_fc_proxy(schedule)
+
+    # Assert
+    assert list(tmp_path.iterdir()) == [schedule]
+
+
+def test_replay_dir_is_created_when_missing(tmp_path: Path):
+    # Arrange
+    schedule = tmp_path / "schedule.json"
+    _write_schedule(schedule, _schedule_payload())
+    replay_dir = tmp_path / "deep" / "nested" / "replay"
+
+    # Act
+    fpr.drive_fc_proxy(schedule, replay_dir=replay_dir)
+
+    # Assert
+    assert (replay_dir / "proxy_drive_report.json").is_file()

e2e/_unit_tests/test_directory_layout.py

@@ -55,6 +55,7 @@ E2E_ROOT = Path(__file__).resolve().parents[1]
         "runner/helpers/outlier_tolerance_evaluator.py",
         "runner/helpers/outage_request_evaluator.py",
         "runner/helpers/blackout_spoof_evaluator.py",
+        "runner/helpers/fc_proxy_runtime.py",
         "fixtures/mock-suite-sat/Dockerfile",
         "fixtures/mock-suite-sat/app.py",
         "fixtures/mock-suite-sat/requirements.txt",

e2e/fixtures/injectors/fc_proxy.py

@@ -154,6 +154,18 @@ class BlackoutSpoofProxy:
     def activation_report(self) -> ProxyAlignmentReport | None:
         return self._activation_report
 
+    @property
+    def window_start_ms(self) -> int:
+        return self._window_start_ms
+
+    @property
+    def window_end_ms(self) -> int:
+        return self._window_end_ms
+
+    @property
+    def spoof_frame_count(self) -> int:
+        return len(self._spoof_gps)
+
     def _proxy_time_ms(self) -> int:
         if not self._activated or self._now_ms_provider is None or self._t0_ms is None:
             raise RuntimeError("proxy not activated — call activate(...) first")

e2e/runner/helpers/fc_proxy_runtime.py

@@ -0,0 +1,119 @@
+"""FC-inbound proxy runtime driver — wraps `BlackoutSpoofProxy` for scenarios.
+
+This is the runtime piece invoked by FT-N-04 (`test_ft_n_04_blackout_spoof`)
+to drive a coordinated GPS spoofing window. The schedule itself is owned
+by `fixtures/injectors/blackout_spoof.py`; the proxy state machine
+(activate / process_inbound_message / in_window) is owned by
+`fixtures/injectors/fc_proxy.BlackoutSpoofProxy`. What was missing — and
+what this module adds — is the scenario-facing entry point that:
+
+1. Loads the schedule from disk via `BlackoutSpoofProxy.from_schedule_file`.
+2. Optionally activates the proxy against a caller-supplied monotonic
+   clock (so the scenario can later verify wall-clock alignment).
+3. Writes a small `proxy_drive_report.json` audit record into
+   `${E2E_SITL_REPLAY_DIR}` so downstream evaluators (the
+   `sitl_observer.read_gps_health_samples` /
+   `read_consistency_check_events` consumers in FT-N-04) can correlate.
+
+This driver is **FDR-replay mode only** — it does NOT plumb the proxy
+into a live MAVLink router/FC inbound transport. The replay-fixture
+builder pre-bakes the spoofed-GPS-rejected events into the FDR JSON
+files that the offline `sitl_observer` reads. Live-mode driving (real
+router + real FC) is a separate live-mode infrastructure ticket.
+
+Public-boundary discipline: imports only stdlib +
+`fixtures.injectors.fc_proxy` (an existing test-side module). Zero
+`from gps_denied_onboard ...` imports.
+"""
+
+from __future__ import annotations
+
+import json
+import os
+from dataclasses import asdict, dataclass
+from pathlib import Path
+from typing import Callable
+
+from fixtures.injectors.fc_proxy import BlackoutSpoofProxy
+
+NowMsProvider = Callable[[], int]
+
+_ENV_VAR = "E2E_SITL_REPLAY_DIR"
+_REPORT_FILENAME = "proxy_drive_report.json"
+
+
+@dataclass(frozen=True)
+class ProxyDriveReport:
+    """Audit record of one `drive_fc_proxy` invocation.
+
+    Persisted as `proxy_drive_report.json` under the replay-dir root so
+    downstream evaluators can confirm the schedule was actually applied
+    rather than silently skipped.
+    """
+
+    schedule_path: str
+    window_start_ms: int
+    window_end_ms: int
+    spoof_frame_count: int
+    alignment_err_ms: int
+    was_replay_mode: bool
+
+
+def drive_fc_proxy(
+    schedule_path: Path,
+    *,
+    now_ms_provider: NowMsProvider | None = None,
+    replay_dir: Path | None = None,
+) -> ProxyDriveReport:
+    """Drive the FC-inbound spoof proxy from `schedule_path`.
+
+    `schedule_path` — JSON written by `blackout_spoof.materialize`.
+    `now_ms_provider` — when supplied, the proxy is activated and the
+        report carries the resulting `alignment_err_ms`. When None,
+        the driver runs in replay mode and reports `alignment_err_ms=0`.
+    `replay_dir` — when supplied (or resolved from `E2E_SITL_REPLAY_DIR`),
+        the report is written as JSON into that directory. When both
+        are absent, no file is written.
+
+    Raises `FileNotFoundError` when `schedule_path` is missing
+    (propagated from `BlackoutSpoofProxy.from_schedule_file`) and
+    `ValueError` (wrapped) when the JSON cannot be parsed.
+    """
+    try:
+        proxy = BlackoutSpoofProxy.from_schedule_file(schedule_path)
+    except json.JSONDecodeError as exc:
+        raise ValueError(
+            f"malformed schedule JSON at {schedule_path}: {exc.msg}"
+        ) from exc
+
+    if now_ms_provider is not None:
+        activation = proxy.activate(now_ms_provider=now_ms_provider)
+        alignment_err_ms = int(activation.alignment_err_ms)
+        was_replay_mode = False
+    else:
+        alignment_err_ms = 0
+        was_replay_mode = True
+
+    report = ProxyDriveReport(
+        schedule_path=str(schedule_path),
+        window_start_ms=proxy.window_start_ms,
+        window_end_ms=proxy.window_end_ms,
+        spoof_frame_count=proxy.spoof_frame_count,
+        alignment_err_ms=alignment_err_ms,
+        was_replay_mode=was_replay_mode,
+    )
+
+    target_dir = replay_dir if replay_dir is not None else _resolve_replay_dir()
+    if target_dir is not None:
+        target_dir.mkdir(parents=True, exist_ok=True)
+        (target_dir / _REPORT_FILENAME).write_text(json.dumps(asdict(report)))
+
+    return report
+
+
+def _resolve_replay_dir() -> Path | None:
+    """Resolve `E2E_SITL_REPLAY_DIR`. Returns None when unset or empty."""
+    raw = os.environ.get(_ENV_VAR, "").strip()
+    if not raw:
+        return None
+    return Path(raw)

e2e/tests/negative/test_ft_n_04_blackout_spoof.py

@@ -222,9 +222,9 @@ def _resolve_frame_sink():  # type: ignore[no-untyped-def]
 
 
 def _drive_fc_proxy(schedule_path: Path) -> None:
-    raise NotImplementedError(
-        "FC-inbound spoof proxy driver is owned by AZ-441 / runner.helpers.fc_proxy_runtime"
-    )
+    from runner.helpers.fc_proxy_runtime import drive_fc_proxy
+
+    drive_fc_proxy(schedule_path)
 
 
 def _resolve_frame_period_ms() -> int: