# Replay — `compose_root` extension for `config.mode == "replay"` + JSONL sink + NoopMavlinkTransport wiring

**Task**: AZ-401_replay_compose
**Name**: Extend `compose_root(config)` with a `config.mode == "replay"` branch — wire `ReplayInputAdapter`, `JsonlReplaySink`, and `NoopMavlinkTransport` into the same C1–C7 + C13 graph as live mode
**Description**: Add a single mode-aware branch inside the existing `compose_root(config)` in `src/gps_denied_onboard/runtime_root/__init__.py` (or the factory module it delegates to). When `config.mode == "live"` the function behaves exactly as today. When `config.mode == "replay"`:

1. Build a `ReplayInputAdapter` from `config.replay.{video_path, tlog_path, pace, time_offset_ms, target_fc_dialect, …}` using the same `CameraCalibration` and `WgsConverter` the live path already constructs.
2. Call `replay_input.open()` → `ReplayInputBundle(frame_source, fc_adapter, clock, …)` and use the three returned strategies as the standard `FrameSource` + `FcAdapter` + `Clock` for the rest of the graph (no further mode awareness past this point).
3. Pick `NoopMavlinkTransport` (replay) instead of `SerialMavlinkTransport` (live) as the `MavlinkTransport` injected into the C8 outbound encoders. The encoders are unchanged — they produce the same byte streams in both modes (replay protocol Invariant 5).
4. Attach a `JsonlReplaySink` as an additional listener on C5's `EstimatorOutput` stream. The live binary's existing downstream observers (C8 outbound to FC, QGC telemetry adapter, C13 FDR) all stay wired in replay — only the C8 outbound transport differs (NoopMavlinkTransport in replay) and only the JsonlReplaySink is added.
5. Wire C1–C7 + C13 exactly as in the live composition (replay protocol Invariant 1 — components see the same interfaces).
6. Refuse construction if any of `BUILD_VIDEO_FILE_FRAME_SOURCE`, `BUILD_TLOG_REPLAY_ADAPTER`, `BUILD_REPLAY_SINK_JSONL` is OFF in replay mode (raise `CompositionError` pointing at the OFF flag).

**Out of scope**: there is **no** separate `compose_replay` function under ADR-011 — replay is a configuration of the single `compose_root`. If a stub `compose_replay` exists today in the codebase (from the v1.0.0 design), it MUST be deleted as part of this task; the runtime_root `__init__.py` exposes only `compose_root` and `compose_operator`.
**Complexity**: 2 points (was 3 in the v1.0.0 spec; shrinks because there is no new composition function, only a config-driven branch + two strategy swaps + one observer attachment)
**Dependencies**: AZ-398 (`FrameSource` + `Clock`); AZ-399 (`TlogReplayFcAdapter`); AZ-400 (`JsonlReplaySink` + `MavlinkTransport` Protocol seam + `NoopMavlinkTransport` + `SerialMavlinkTransport` retrofit); AZ-405 (`ReplayInputAdapter`); AZ-269 / AZ-270 (config — `Config.mode` field + `Config.replay` sub-config); AZ-263 (`runtime_root` bootstrap); AZ-266 (logging); AZ-272 (FDR record schema); AZ-279 (`WgsConverter`); AZ-390 (E-C8 `FcAdapter` Protocol the tlog adapter implements); the C1–C5 component factory APIs (already exist).
**Component**: replay-composition (epic AZ-265 / E-DEMO-REPLAY) — branch lives in `runtime_root/__init__.py` (or the factory module the composition root already delegates to).
**Tracker**: AZ-401
**Epic**: AZ-265 (E-DEMO-REPLAY)

### Document Dependencies

- `_docs/02_document/contracts/replay/replay_protocol.md` (v2.0.0) — Invariants 1, 5, 9, 11, 12 + the composition-root extension narrative.
- `_docs/02_document/architecture.md` — **ADR-011** (replay-as-configuration; THE design-defining decision for this task) + ADR-001 / ADR-002 / ADR-009.
- `_docs/02_document/module-layout.md` — Build-Time Exclusion Map (the three replay-mode `BUILD_*` flags default ON in airborne); `runtime_root` cross-cutting entry.
- `_docs/02_document/contracts/c5_state/state_estimator_protocol.md` — `EstimatorOutput` consumed by the JSONL sink.
- `_docs/02_document/contracts/c8_fc_adapter/fc_adapter_protocol.md` — `FcAdapter` Protocol + the new tiny `MavlinkTransport` seam introduced by AZ-400.

## Problem

Without this task, the replay-only strategies (`ReplayInputAdapter` from `replay_input/`, `JsonlReplaySink`, `NoopMavlinkTransport`) have no integration point with the airborne composition root; `config.mode == "replay"` is parsed by the config loader but not acted upon; the per-frame runtime loop is identical to live but no UI-tailable JSONL output is produced. This is the single point of mode awareness in the codebase (replay protocol Invariants 1 + 5).

## Outcome

- `src/gps_denied_onboard/runtime_root/__init__.py` (or the factory module it delegates to) exposes one `compose_root(config) -> Runtime` that branches internally on `config.mode in {"live", "replay"}`. No new public function. The branch:
  - In `live`: behaves exactly as today (no behaviour change for the live path).
  - In `replay`: builds `ReplayInputAdapter`, calls `.open()`, picks `NoopMavlinkTransport` for C8 outbound, attaches `JsonlReplaySink` to C5's `EstimatorOutput` stream, and otherwise wires C1–C7 + C13 identically.
- `Config.mode: Literal["live", "replay"] = "live"` field on the config DTO (default live; replay opt-in). Plus a `Config.replay` sub-config holding `video_path`, `tlog_path`, `output_path`, `pace`, `time_offset_ms`, `target_fc_dialect`, `auto_sync` sub-block. Owned by the AZ-269 / AZ-270 config schema task — this task adds the fields if AZ-269 / AZ-270 haven't landed them yet (the config schema is a coordinate of this and the AZ-269 / AZ-270 / AZ-405 tasks; the schema lives at `src/gps_denied_onboard/config/`).
- Build-flag check at startup: when `config.mode == "replay"` and any of the three replay-mode `BUILD_*` flags is OFF, raises `CompositionError("replay mode requires BUILD_VIDEO_FILE_FRAME_SOURCE / BUILD_TLOG_REPLAY_ADAPTER / BUILD_REPLAY_SINK_JSONL to be ON; flag <name> is OFF in this build")`. In live mode the flags are not checked (the OFF setting on a replay flag does not block live mode).
- The legacy stub `runtime_root/replay.py` + the legacy `compose_replay` export (if present) are deleted as part of this task; replay is a configuration of `compose_root`, not a sibling composition root. The deletion is justified by the dead-code rule in `coderule.mdc` (no remaining usages once this task lands).
- INFO log on startup, in replay mode: `kind="replay.compose_root.ready"` with `{config_path, calib_path, pace, time_offset_ms, video_path, tlog_path, output_path}`.
- INFO log on startup, in live mode: existing live `compose_root.ready` log unchanged.
- Unit tests:
  - `test_compose_root_live_unchanged`: with `config.mode == "live"`, the returned `Runtime` has the same shape (same strategy classes for FrameSource/FcAdapter/MavlinkTransport/Sink set) as today.
  - `test_compose_root_replay_wires_replay_strategies`: with `config.mode == "replay"`, `isinstance(runtime.frame_source, VideoFileFrameSource)`, `isinstance(runtime.fc_adapter, TlogReplayFcAdapter)`, `isinstance(runtime.mavlink_transport, NoopMavlinkTransport)`, and a `JsonlReplaySink` is attached to C5's `EstimatorOutput` stream.
  - `test_compose_root_replay_rejects_off_flag`: with `BUILD_VIDEO_FILE_FRAME_SOURCE=OFF` and `config.mode == "replay"`, `compose_root(config)` raises `CompositionError("BUILD_VIDEO_FILE_FRAME_SOURCE is OFF; replay mode requires it")`.
  - `test_compose_root_replay_single_clock`: the same `Clock` instance is injected into all components that need one (replay protocol Invariant 2 — `id()` equality across consumers).
  - `test_compose_root_no_compose_replay_export`: `from gps_denied_onboard.runtime_root import compose_replay` raises `ImportError` (the legacy function is deleted).
  - `test_compose_root_replay_jsonl_sink_emits_per_tick`: drive 10 frames through the wired runtime; assert `JsonlReplaySink.emit` was called exactly 10 times with `EstimatorOutput` instances.
  - `test_compose_root_replay_noop_transport_swallows_emits`: drive a known sequence of EstimatorOutput through the runtime; assert `NoopMavlinkTransport.bytes_written() > 0` (C8 encoders still produce bytes) AND the bytes never reach any wire-attached transport.

## Scope

### Included
- The `config.mode` branch inside `compose_root`.
- `Config.mode` + `Config.replay` schema additions (if not already present).
- Deletion of `runtime_root/replay.py` + the `compose_replay` export.
- Build-flag check at startup for replay mode.
- INFO logs.
- All unit tests listed above.

### Excluded
- CLI argparse + entrypoint — owned by AZ-402.
- `ReplayInputAdapter` itself — owned by AZ-405.
- `JsonlReplaySink` / `NoopMavlinkTransport` / `MavlinkTransport` Protocol seam / `SerialMavlinkTransport` retrofit — owned by AZ-400.
- `TlogReplayFcAdapter` — owned by AZ-399.
- `VideoFileFrameSource` / `LiveCameraFrameSource` / `Clock` strategies — owned by AZ-398.
- E2E replay fixture test — owned by AZ-404.
- Auto-sync logic — owned by AZ-405.

## Acceptance Criteria

**AC-1: Single composition root** — `from gps_denied_onboard.runtime_root import compose_root, compose_operator` works; `from gps_denied_onboard.runtime_root import compose_replay` raises `ImportError`. There is only one entry-point function per binary track.

**AC-2: Live mode unchanged** — with `config.mode == "live"` (or omitted; default is live), `compose_root(config)` produces a `Runtime` whose strategy classes match the pre-task baseline (snapshot test: serialise the class names of all wired strategies; baseline file checked into the repo; this test fails if the live wiring changed inadvertently).

**AC-3: Replay mode wires replay strategies** — with `config.mode == "replay"`, the returned `Runtime` has:
- `frame_source: VideoFileFrameSource`
- `fc_adapter: TlogReplayFcAdapter`
- `mavlink_transport: NoopMavlinkTransport`
- A `JsonlReplaySink` registered as a listener on C5's `EstimatorOutput` stream

**AC-4: Replay-mode build-flag check** — with `BUILD_VIDEO_FILE_FRAME_SOURCE=OFF` and `config.mode == "replay"`, `compose_root(config)` raises `CompositionError("BUILD_VIDEO_FILE_FRAME_SOURCE is OFF; replay mode requires it")`. Same for the other two flags. With the SAME `BUILD_*` flag OFF but `config.mode == "live"`, `compose_root(config)` succeeds (live mode does not require the replay flags).

**AC-5: Clock injection** — `config.mode == "replay"` with `pace == "asap"` injects `TlogDerivedClock`; with `pace == "realtime"` injects `WallClock`. The SAME `Clock` instance is injected into every component that consumes one (`id()` equality across the C1, C5, C8 consumers; replay protocol Invariant 2).

**AC-6: JSONL sink emits per tick** — drive 10 frames through the wired runtime (using a `FakeFrameSource` + fake `TlogReplayFcAdapter` from test fixtures); assert `JsonlReplaySink.emit` is called exactly 10 times with `EstimatorOutput` instances.

**AC-7: No mode-aware imports in components** — AST scan asserts that `compose_root` is the ONLY file that imports BOTH `LiveCameraFrameSource` AND `VideoFileFrameSource` (i.e., no component sees both strategy classes). Replay-aware logic is confined to the composition root + the replay strategies + the `replay_input/` coordinator.

**AC-8: Public APIs only across components** — assert that the replay-mode branch imports ONLY `__init__.py` re-exports of each component (per `module-layout.md` Layer-3 / Layer-4 rules). CI-style AST scan in the unit test.

**AC-9: NoopMavlinkTransport swallows C8 outbound bytes** — drive a known EstimatorOutput sequence through the runtime in replay mode; assert `NoopMavlinkTransport.bytes_written() > 0` (the C8 encoders run their signing handshake + GPS_INPUT encoding) AND no I/O reached any wire-attached transport (verified by the absence of any open file descriptor / serial port mock activity).

**AC-10: Operator pre-flight C6 cache reused identically** — wire a stub C6 `FaissDescriptorIndex` populated with a known descriptor; run replay mode against the wired runtime; assert C2's `lookup()` returns the expected tile ID. Demonstrates that C6 is fully wired in replay (replay protocol Invariant 12 — no replay-specific cache shape).

## Non-Functional Requirements

- `compose_root` p99 ≤ 1 s in either mode (one-time startup cost; epic NFT cold-start ≤ 5 s).
- The branch logic itself adds ≤ 50 ms p99 to live-mode startup (since the live branch should not pay any replay tax).

## Constraints

- ADR-001 / ADR-002 / ADR-009 / **ADR-011** unchanged.
- Public API discipline (Layer-3 / Layer-4 from `module-layout.md`).
- C1–C7 + C13 components MUST remain mode-agnostic (replay protocol Invariant 1; AST scan enforces in AZ-404).
- All time-driven logic uses injected `Clock` (replay protocol Invariant 2).
- No HTTP server in the airborne binary regardless of mode.
- NO standalone composition root for replay (replay protocol + ADR-011).

## Risks & Mitigation

- **R-DEMO-4 (production C1–C5 paths bake real-time-cadence assumptions)** — *Mitigation*: `Clock` injection (replay protocol Invariant 2); inherits from AZ-398.
- **R-DEMO-5 (live and replay diverge silently because they share one composition root)** — *Mitigation*: AC-2 (live snapshot test) + AC-7 (no mode-aware imports outside compose_root) + AZ-404's AST scan on Invariant 1. Any drift becomes a test failure.
- **Risk: deleting `runtime_root/replay.py` breaks consumers we forgot to update** — *Mitigation*: AC-1 explicitly asserts the import fails; before this task lands, grep for `compose_replay` across the repo and update each call site to `compose_root(config_with_mode_replay)`. The grep is part of the implementation step; the test assertion catches any miss.
- **Risk: `Config.mode` default of "live" silently breaks an existing config file that lacked the field** — *Mitigation*: the default is "live", which is also the legacy behaviour; no existing config file needs to change.

## Runtime Completeness

- **Named capability**: single composition root that resolves `config.mode` to the correct strategy set + observer wiring.
- **Production code**: real config-mode branch, real strategy wiring, real JSONL sink attachment, real noop-transport injection, real build-flag check.
- **Allowed external stubs**: test fakes only (FakeFrameSource, FakeFcAdapter, FakeReplaySink, FakeMavlinkTransport, FakeC6DescriptorIndex) for unit tests.
- **Unacceptable substitutes**: keeping a separate `compose_replay` function "for clarity" (defeats ADR-011 — the single composition root IS the architectural mechanism for mode-agnosticism); branching on `config.mode` inside component code (defeats replay protocol Invariant 1).

## Contract

Implements `_docs/02_document/contracts/replay/replay_protocol.md` (v2.0.0) — composition-root extension + Invariants 1, 5, 9, 11, 12. Operationalises ADR-011.
