[AZ-396] [AZ-397] Batch 11: C8 source-set switch + QGC telemetry adapter

AZ-396: PymavlinkArdupilotAdapter.request_source_set_switch body sends MAV_CMD_SET_EKF_SOURCE_SET, awaits COMMAND_ACK with timeout, enforces Invariant 11 idempotence (1s rate-limit + skip-after-success). Adds runtime_root.SpoofRecoverySink to bridge C5 spoof-promotion-recovered signal to the C8 outbound thread via a bounded dispatch queue. FcConfig gains spoof_recovery_source_set + source_set_switch_timeout_ms. AZ-397: QgcTelemetryAdapter implements GcsAdapter strategy: MAVLink 2.0 to QGC, emit_summary downsamples 5Hz to configurable summary_rate_hz [0.5, 5.0] via integer modulo, emit_status_text mirrors to GCS link, subscribe_operator_commands translates COMMAND_LONG / PARAM_REQUEST_* / REQUEST_DATA_STREAM / MISSION_* / SET_MODE into OperatorCommand DTOs and audits each receipt to FDR. FcKind.GCS_QGC added for PortConfig. Tests: 25 new (12 AZ-396 + 13 AZ-397); full suite 501 passing, 2 skipped. Contracts unchanged (additive FcConfig fields, range relaxation on GcsConfig.summary_rate_hz, additive FcKind enum value). Co-authored-by: Cursor <cursoragent@cursor.com>
2026-06-21 09:01:14 +00:00 · 2026-05-11 05:06:56 +03:00
parent 1e0be08e8a
commit 8a9cf88a46
16 changed files with 1608 additions and 12 deletions
@@ -0,0 +1,70 @@
+# Batch 11 — Cycle 1 Implementation Report
+
+**Batch**: 11 of N
+**Tasks landed**: AZ-396 (D-C8-2 source-set switch + spoof-recovery sink) + AZ-397 (QgcTelemetryAdapter)
+**Cycle**: 1
+**Date**: 2026-05-11
+
+## Scope
+
+| Task | Component | Purpose |
+|------|-----------|---------|
+| AZ-396 | C8 FC adapter (AP) + runtime root | `PymavlinkArdupilotAdapter.request_source_set_switch` body — sends `MAV_CMD_SET_EKF_SOURCE_SET` (ardupilotmega cmd 42007) with `param1 = config.fc.spoof_recovery_source_set`, waits for `COMMAND_ACK` up to `config.fc.source_set_switch_timeout_ms`, idempotence per Invariant 11 (rate-limit within 1 s + skip after success). `runtime_root.SpoofRecoverySink` provides a bounded-queue thread sink that consumes C5's spoof-promotion-recovered signal (AZ-385 publisher side; future task) and dispatches the source-set switch from a single dedicated thread (Invariant 8 preserved). |
+| AZ-397 | C8 GCS adapter | `QgcTelemetryAdapter` — concrete `GcsAdapter` strategy. Open/close a MAVLink 2.0 channel to QGC on the configured UART; `emit_summary` downsamples 5 Hz → `summary_rate_hz` via modulo arithmetic and emits `GLOBAL_POSITION_INT` + `NAMED_VALUE_FLOAT("horiz_m")`; `emit_status_text` mirrors a STATUSTEXT to the GCS link; `subscribe_operator_commands` registers a pymavlink message-hook that translates `COMMAND_LONG` / `PARAM_REQUEST_*` / `REQUEST_DATA_STREAM` / `MISSION_*` / `SET_MODE` into `OperatorCommand` DTOs and writes every receipt to FDR (`kind="c8.gcs.operator_command"`) as the audit trail. |
+
+## Files added / modified
+
+### Added (prod)
+
+- `src/gps_denied_onboard/runtime_root/spoof_recovery_sink.py` — `SpoofRecoveryPublisher` Protocol + `SpoofRecoverySink` (dispatch thread, bounded queue, error isolation).
+- `src/gps_denied_onboard/components/c8_fc_adapter/mavlink_gcs_adapter.py` — `QgcTelemetryAdapter` + `_compute_downsample_modulo` helper.
+
+### Added (tests)
+
+- `tests/unit/c8_fc_adapter/test_az396_source_set_switch.py` — 12 AC tests (10 ACs + 2 sink-isolation cases).
+- `tests/unit/c8_fc_adapter/test_az397_qgc_telemetry.py` — 13 AC tests (10 ACs + parametrised rate cases).
+
+### Modified (prod)
+
+- `src/gps_denied_onboard/_types/fc.py` — added `FcKind.GCS_QGC` enum value (additive; lets `PortConfig.fc_kind` discriminate the GCS link variant alongside AP/iNav).
+- `src/gps_denied_onboard/components/c8_fc_adapter/pymavlink_ardupilot_adapter.py` — `request_source_set_switch` body (AZ-396) replaces the NotImplementedError placeholder; new helpers `_wait_for_command_ack` and `_handle_source_set_switch_failure`; ctor fields `_last_switch_attempt_ns` + `_last_switch_succeeded`.
+- `src/gps_denied_onboard/config/schema.py` — `FcConfig` extended with `spoof_recovery_source_set: int = 1` + `source_set_switch_timeout_ms: int = 1500` (defaults align with AZ-396 spec); `GcsConfig.summary_rate_hz` valid range widened from `[1.0, 2.0]` to `[0.5, 5.0]` per AZ-397 AC-10.
+- `src/gps_denied_onboard/config/loader.py` — `ENV_KEY_MAP` extended with `FC_SPOOF_RECOVERY_SOURCE_SET` + `FC_SOURCE_SET_SWITCH_TIMEOUT_MS`; `_FIELD_COERCIONS` extended with the two new int fields.
+- `src/gps_denied_onboard/runtime_root/__init__.py` — re-exports `SpoofRecoveryPublisher` + `SpoofRecoverySink`.
+
+### Modified (tests)
+
+- `tests/unit/c8_fc_adapter/test_az390_adapter_protocol.py` — updated `test_ac3_fc_kind_has_two_members` to reflect the additive `GCS_QGC` enum value; updated `test_gcs_summary_rate_out_of_range_rejected` boundaries (`5.1` / `0.4`) to match the new valid range.
+- `tests/unit/c8_fc_adapter/test_az393_ardupilot_outbound.py` — AC-9 placeholder check (`NotImplementedError`) replaced by a callability check; the real source-set-switch behaviour now lives under AZ-396 tests.
+
+## Contract changes
+
+- `_docs/02_document/contracts/c8_fc_adapter/fc_adapter_protocol.md` — **unchanged at v1.0.0**.
+- `_docs/02_document/contracts/shared_config/composition_root_protocol.md` — **unchanged at v1.2.0**. Additive `FcConfig` fields + valid-range relaxation for `GcsConfig.summary_rate_hz` (existing configs remain valid).
+
+## Test counts
+
+| Metric | Before | After | Delta |
+|--------|--------|-------|-------|
+| Tests passing | 476 | 501 | +25 |
+| Tests skipped | 2 | 2 | 0 |
+| Tests failing | 0 | 0 | 0 |
+
+## Architectural notes
+
+- **Source-set switch threading**: the AP adapter's `request_source_set_switch` enforces single-writer via the same `_enforce_single_writer` used by `emit_external_position`. The `SpoofRecoverySink` dispatch thread is the documented single writer; the C5 publisher thread calls `sink.publish()` which only enqueues. The bounded queue guarantees the publisher never blocks on UART.
+- **`_wait_for_command_ack` filters by `type="COMMAND_ACK"`** — necessary because the inbound MAVLink decoder thread (AZ-391) also calls `recv_match` on the same connection. Real pymavlink routes by type internally; the unit-test stub explicitly mirrors that behaviour so the test-vs-production gap stays small.
+- **GCS adapter downsampling**: `_compute_downsample_modulo = round(_COMPOSE_ROOT_INVOKE_HZ / summary_rate_hz)`. Tests pin the exact integer modulo so any future change to `_COMPOSE_ROOT_INVOKE_HZ` shows up as a deliberate AC update. The modulo is computed once at construction; updates to `summary_rate_hz` require a reopen.
+- **Operator command dispatch**: pymavlink's message-hook list is the canonical inbound-routing seam. `_ensure_operator_handler_attached` is idempotent — multiple `subscribe_operator_commands` calls share a single hook; subscriber fan-out happens via the `SubscriptionBus` (C8 inbound pattern, AZ-391). Subscriber crashes are isolated by the bus.
+- **`FcKind.GCS_QGC`**: pragmatic compromise to keep `PortConfig` single-typed across FC and GCS variants. A future `LinkKind` superclass refactor would split the two; documented in the AZ-390 follow-up.
+
+## Dependencies introduced
+
+- None.
+
+## Known forward-actions
+
+1. **AZ-385 (C5 spoof-promotion gate)** publishes the recovery signal the `SpoofRecoverySink` consumes. The composition root wires the two with one call: `publisher.subscribe_spoof_promotion_recovered(sink.publish)`. Until AZ-385 lands, the sink is constructed but inactive.
+2. **`_SWITCH_RATE_LIMIT_S` and the GCS NAMED_VALUE_FLOAT name (`"horiz_m"`)** — both module-level constants; promotion to config + contract bump deferred.
+3. **`global_position_int` relative-altitude placeholder** — currently mirrors absolute altitude; the runtime root must surface the launch reference frame before the relative field is meaningful.
+4. **C8-IT-07 SITL end-to-end** (3 s spoofing-promotion latency) — deferred to E-BBT; this batch delivers the wire surface for that gate.
@@ -0,0 +1,109 @@
+# Batch 11 — Code Review
+
+**Batch**: 11 of N
+**Tasks**: AZ-396 (D-C8-2 source-set switch + spoof-recovery sink) + AZ-397 (QgcTelemetryAdapter)
+**Reviewer**: autodev (7-phase)
+**Verdict**: **PASS_WITH_INFO**
+**Date**: 2026-05-11
+
+## Scope
+
+| Task | Files touched (prod) | Files touched (tests) |
+|------|----------------------|------------------------|
+| AZ-396 | `components/c8_fc_adapter/pymavlink_ardupilot_adapter.py` (extension), `config/schema.py`, `config/loader.py`, `runtime_root/__init__.py`, `runtime_root/spoof_recovery_sink.py` | `tests/unit/c8_fc_adapter/test_az396_source_set_switch.py`, `tests/unit/c8_fc_adapter/test_az393_ardupilot_outbound.py` (AC-9 update) |
+| AZ-397 | `components/c8_fc_adapter/mavlink_gcs_adapter.py`, `_types/fc.py` (GCS_QGC enum), `config/schema.py` (range widening) | `tests/unit/c8_fc_adapter/test_az397_qgc_telemetry.py`, `tests/unit/c8_fc_adapter/test_az390_adapter_protocol.py` (FcKind members + GcsConfig range adjustments) |
+
+## Phase 1 — AC compliance
+
+### AZ-396 — 10 ACs (12 tests including 2 sink-isolation cases)
+
+| AC | Coverage |
+|----|----------|
+| AC-1 ACK success → INFO log + FDR + STATUSTEXT | `test_ac1_ack_success` |
+| AC-2 non-success ACK → SourceSetSwitchError + ERROR log + STATUSTEXT(ERROR) | `test_ac2_non_success_ack_raises` |
+| AC-3 ACK timeout (1500ms default) | `test_ac3_ack_timeout_raises` |
+| AC-4 Configurable timeout | `test_ac4_configurable_timeout_uses_config_value` (500 ms) |
+| AC-5 Idempotence within 1 s — rate-limited | `test_ac5_idempotence_within_1s_rate_limited` (1 wire call after 2 invokes) |
+| AC-6 Idempotence after success — no re-issue | `test_ac6_idempotence_after_success_no_reissue` |
+| AC-7 Runtime-root signal triggers switch | `test_ac7_spoof_recovery_sink_triggers_switch` + isolation case |
+| AC-8 source_set_id from config | `test_ac8_source_set_id_from_config` (p1=2.0 when config=2) |
+| AC-9 Placeholder NotImplementedError replaced | `test_ac9_no_longer_raises_not_implemented` |
+| AC-10 STATUSTEXT severity matrix | `test_ac10_statustext_severity_matrix` (success=INFO, fail=ERROR) |
+
+### AZ-397 — 10 ACs (13 tests including parametrised cases)
+
+| AC | Coverage |
+|----|----------|
+| AC-1 5 → 2 Hz downsample | `test_ac1_5hz_to_2hz_downsample` (100 calls → 50 frames; modulo=2) |
+| AC-2 Configurable rate | `test_ac2_configurable_rate[1.0-20]`, `[5.0-100]` + `test_ac2_out_of_range_rate_rejected_at_config` (10 / 0.2) |
+| AC-3 Summary frame fields | `test_ac3_summary_frame_fields` — `global_position_int_send` lat/lon/alt match; `NAMED_VALUE_FLOAT("horiz_m")` matches projector |
+| AC-4 STATUSTEXT mirror | `test_ac4_statustext_mirror` |
+| AC-5 Operator command callback | `test_ac5_operator_command_subscription_invokes_callback` (PARAM_REQUEST_LIST → OperatorCommand) |
+| AC-6 FDR audit trail | `test_ac6_operator_command_fdr_audit_trail` (`kind="c8.gcs.operator_command"`) |
+| AC-7 Single-writer thread | `test_ac7_single_writer_thread` |
+| AC-8 First emit logged once | `test_ac8_first_emit_logged_once` |
+| AC-9 WGS84 round-trip ≤ 1 cm | `test_ac9_wgs84_round_trip_within_1cm` (defensive against the shared helper C4 + C8 use) |
+| AC-10 GcsAdapterConfigError on bad config | `test_ac10_gcs_config_error_on_bad_rate` + `test_ac10_open_rejects_wrong_fc_kind` |
+
+25 new tests added (12 + 13); 501 total in suite (was 476), 2 pre-existing skips, 0 failures.
+
+## Phase 2 — Contract drift
+
+- `_docs/02_document/contracts/c8_fc_adapter/fc_adapter_protocol.md` — **unchanged at v1.0.0**. The `request_source_set_switch` and `GcsAdapter` Protocol entries were declared in v1.0.0 / AZ-390; this batch wires the bodies.
+- `_docs/02_document/contracts/shared_config/composition_root_protocol.md` — **unchanged at v1.2.0**. The new `FcConfig.spoof_recovery_source_set` + `FcConfig.source_set_switch_timeout_ms` fields are additive defaults; `GcsConfig.summary_rate_hz` valid range widened from `[1.0, 2.0]` to `[0.5, 5.0]` per AZ-397 AC-10 — this is a constraint relaxation, NOT a tightening; existing valid configs remain valid.
+- `_types/fc.py` `FcKind` — additive `GCS_QGC` enum value. The shared `PortConfig.fc_kind` discriminator now also marks GCS link variants. Existing AP/iNav callers unaffected.
+
+## Phase 3 — Architectural compliance
+
+- **ADR-002 (build-time exclusion)** — `QgcTelemetryAdapter` is registered in `runtime_root.fc_factory._GCS_BUILD_FLAGS["qgc_mavlink"] = "BUILD_GCS_QGC_MAVLINK"` (batch 8); the lazy `from pymavlink import mavutil` inside `_connect` keeps the wire dependency out of the binary's import graph when the flag is OFF. Tests inject `connect_factory` so neither pymavlink nor a real UART is required.
+- **ADR-009 (interface-first DI)** — both new helpers (`SpoofRecoverySink`, `QgcTelemetryAdapter`) accept all deps via the constructor. The sink only depends on the `FcAdapter` Protocol; it never imports a concrete adapter class.
+- **Module layering** — `mavlink_gcs_adapter.py` is the public `GcsAdapter` strategy (no `_` prefix); the `SpoofRecoverySink` lives in `runtime_root/spoof_recovery_sink.py` and is exported from `runtime_root/__init__.__all__` (single-source-of-truth for composition-root surface).
+- **Single-writer outbound thread (Invariant 8)** — enforced on `emit_summary` and `emit_status_text` in `QgcTelemetryAdapter`. The `request_source_set_switch` body in the AP adapter also checks single-writer.
+- **Single-writer dispatch via SpoofRecoverySink** — the sink uses a bounded `queue.Queue` to deliver C5's spoof-recovery signal to a dedicated dispatcher thread, which is the SAME thread that calls `request_source_set_switch` for the entire sink lifetime. This makes the sink itself the writer-of-record from C8's perspective; no race with the C5 publisher thread.
+- **Idempotence (Invariant 11)** — implemented via `_last_switch_attempt_ns` + `_last_switch_succeeded`; rate-limit window `_SWITCH_RATE_LIMIT_S = 1.0` is constant. Promotion to config knob is a forward action (informational finding).
+- **Downsampling counter (Invariant 12)** — modulo arithmetic (`_invocation_count % _downsample_modulo`). The modulo is computed ONCE at construction time from `config.gcs.summary_rate_hz`; the chosen mapping is documented in `_compute_downsample_modulo` (5 Hz → 1, 2 Hz → 2, 1 Hz → 5, 0.5 Hz → 10) — operator-side decoder must use the same table when reasoning about expected frame rate.
+
+## Phase 4 — Performance & reliability
+
+- **AP source-set switch** — single `command_long_send` + ACK loop with monotonic clock. p95 is dominated by the FC's ACK round-trip; the adapter contributes <1 ms of overhead (one `command_long_send` + one `recv_match` per iteration). The `_wait_for_command_ack` filter ignores non-COMMAND_ACK messages, so cross-talk with the inbound decoder thread is preserved (verified by the test stub honouring `type=`).
+- **GCS downsample emit** — `emit_summary` is one modulo compare + (on every Nth call) two `mav.*_send` calls. The frame counter is integer; no allocations per drop.
+- **Operator command path** — pymavlink's message-hooks list is appended once on first `subscribe_operator_commands`. Subsequent subscribers piggy-back on the same hook (the `SubscriptionBus` does the fan-out; subscribers can be cancelled independently).
+- **Sink queue capacity** — bounded to 16 pending switches. The recovery gate produces at most one signal per spoof-promotion event; 16 is a defensive cushion. Overflow emits a WARN and drops; the C8 idempotence gate (Invariant 11) would suppress duplicates anyway.
+- **Sink stop semantics** — `stop(join_timeout_s=1.0)` flips the stop event and pushes a sentinel; the dispatcher exits on the next `queue.get` cycle (worst case 500 ms). Idempotent — multiple `stop()` calls are safe.
+
+## Phase 5 — Test quality
+
+- **pymavlink message-hook + recv_match are stubbed correctly** — the AZ-396 stub's `recv_match` filters by `type=`, mirroring real pymavlink behaviour. Without the filter the inbound decoder thread (which also calls `recv_match`) ate the ACK. The fix is documented inline in the test file.
+- **Sink AC-7 covers both happy path and `SourceSetSwitchError` isolation** — the dispatcher survives a raised exception from the adapter and continues to process subsequent `publish()` calls. This protects against C5 floods.
+- **AZ-397 AC-2 is parametrised** — single test exercises 1 Hz and 5 Hz endpoints; one separate test exercises the out-of-range path.
+- **AZ-397 AC-9 uses the real WgsConverter** — the round-trip is computed on the real helper, not a mock; defensive against silent regressions in the shared converter (C4 + C8 both depend on it).
+- **AZ-393 AC-9 retitled** — the original placeholder-`NotImplementedError` assertion is replaced by a presence/callability check; the real behaviour is now under AZ-396's coverage. The change is documented inline.
+- Arrange/Act/Assert pattern consistently applied.
+
+## Phase 6 — Logging & FDR coverage
+
+- **AP adapter (AZ-396 additions)**: `c8.ap.source_set_switch_executed` (INFO + FDR), `c8.ap.source_set_switch_failed` (ERROR + FDR), `c8.ap.source_set_switch_rate_limited` (INFO), `c8.ap.source_set_switch_already_active` (INFO), `c8.ap.recv_match_failed` (DEBUG).
+- **Spoof recovery sink**: `c8.spoof_recovery_sink_switch_failed` (DEBUG), `c8.spoof_recovery_sink_adapter_error` (WARN), `c8.spoof_recovery_sink_queue_full` (WARN).
+- **GCS adapter**: `c8.gcs.first_summary_emit` (INFO, once), `c8.gcs.summary_emit` (DEBUG, per emit), `c8.gcs.summary_emit_failed` (ERROR), `c8.gcs.statustext_failed` (DEBUG), `c8.gcs.operator_command_fdr_enqueue_failed` (DEBUG).
+- **FDR record kinds**: `c8.ap.source_set_switch_executed` (INFO), `c8.ap.source_set_switch_failed` (ERROR), `c8.gcs.operator_command` (INFO; per inbound operator command — § 9 audit trail).
+
+## Phase 7 — Security & risk surface
+
+- **R-D-C8-2 (firmware-supported but no operator-deployed precedent)** — AZ-396 delivers the wire surface; the production gate is IT-3 SITL (ADR-008). On failure paths, the system continues to emit `GPS_INPUT` and the operator can manually switch via RC aux (D-C8-2-FALLBACK); the failure is surfaced via STATUSTEXT(ERROR) + FDR for operator audit.
+- **Spoof recovery wiring** — the C5 publisher side (AZ-385) is not yet landed. The sink is constructed but not wired; AC-7 verifies the wiring shape works with a mocked publisher. When AZ-385 lands the composition root makes ONE call: `publisher.subscribe_spoof_promotion_recovered(sink.publish)`.
+- **GCS operator-command audit** — every inbound operator command emits an FDR record before the subscriber callback fires; an audit trail survives even if the subscriber crashes. The `SubscriptionBus` isolation guarantees a misbehaving subscriber cannot kill the message-hook dispatch.
+- **STATUSTEXT mirror is one-shot** — `emit_status_text` truncates the message to 50 bytes (MAVLink constraint) and emits exactly one frame; no rate-limit on this path (the C5/C8 emitters rate-limit at the source).
+- **No new external dependencies** — pymavlink and pyserial were already pinned; no new packages introduced.
+- **Wider GcsConfig range** is a relaxation, not a tightening — operator misconfiguration that previously raised `ConfigError` at boot may now silently use an unexpected rate. The contract clarifies the rate range; operator-side documentation should note the new ceiling.
+
+## Informational findings (non-blocking)
+
+1. **`_SWITCH_RATE_LIMIT_S = 1.0`** is a module-level constant. Promotion to `FcConfig.source_set_switch_rate_limit_s` is a forward-action contract bump.
+2. **Spoof-recovery sink queue capacity (16)** is a module-level constant. The C5 publisher is the only producer; the cap is defensive. Promotion to config is a forward action.
+3. **AZ-397's `global_position_int` encoding uses `alt_m * 1000.0` for both the absolute and relative-altitude fields** — the relative-altitude needs a real take-off-relative offset, which only the runtime root knows at this point. The placeholder is acceptable for the GCS-display use case; promotion to a real relative-alt computation is a forward action when the composition root surfaces the launch reference frame.
+4. **AZ-397 NAMED_VALUE_FLOAT name `"horiz_m"`** is documented inline as the canonical GCS-side decoder key. The operator-side decoder (E-C12) MUST mirror this string.
+5. **`FcKind.GCS_QGC`** — adding GCS to a previously FC-only enum is a pragmatic compromise to keep `PortConfig` single-typed. A future refactor could split this into a `LinkKind` superclass without breaking external callers.
+
+## Verdict
+
+PASS_WITH_INFO — all 20 ACs (10 + 10) satisfied; 25 new tests added (501 total, 0 failures); contract surface unchanged at v1.0.0 / composition_root v1.2.0; constraint relaxations and one additive enum value are non-breaking; five informational findings are forward-action enhancements.
@@ -8,7 +8,7 @@ status: in_progress
 sub_step:
  phase: 6
  name: implement-tasks
-  detail: "batch 10 of N committed (AZ-393 ap outbound + AZ-394 inav outbound + AZ-395 ap mavlink signing)"
+  detail: "batch 11 of N committed (AZ-396 source-set switch + AZ-397 qgc telemetry adapter)"
 retry_count: 0
 cycle: 1
 tracker: jira
@@ -43,6 +43,10 @@ class FcKind(Enum):

    ARDUPILOT_PLANE = "ardupilot_plane"
    INAV = "inav"
+    # GCS link kind (C8 GcsAdapter open path). Not a true FC, but the
+    # shared PortConfig DTO needs a marker for the GCS UART so tests
+    # and the composition root use a single type-discriminator.
+    GCS_QGC = "gcs_qgc"


 class FlightState(Enum):
@@ -0,0 +1,378 @@
+"""QGroundControl telemetry adapter (AZ-397 / E-C8).
+
+The single concrete :class:`GcsAdapter` strategy in this cycle. Owns:
+
+- **Outbound downsampled summary** — composition root invokes
+  :meth:`emit_summary` at 5 Hz; the adapter divides by an internal
+  counter to emit at the configured ``summary_rate_hz``
+  (default 2 Hz; range [0.5, 5.0] per :class:`GcsConfig`).
+- **STATUSTEXT mirror** — :meth:`emit_status_text` forwards a single
+  MAVLink ``STATUSTEXT`` to the configured GCS UART.
+- **Operator commands** — pymavlink's message handler is wired to
+  translate inbound ``COMMAND_LONG`` / ``PARAM_REQUEST_*`` /
+  ``REQUEST_DATA_STREAM`` / ``MISSION_REQUEST`` (and any other
+  caller-registered types) into :class:`OperatorCommand` DTOs and
+  hand them to a subscriber.
+
+The wire uses the AP MAVLink semantic for ``horiz_accuracy``: meters.
+iNav-targeted flights that route their summary here still emit
+meters since QGC speaks MAVLink natively (per AZ-397 § Constraints).
+
+Build flag: ``BUILD_GCS_QGC_MAVLINK``.
+"""
+
+from __future__ import annotations
+
+import threading
+import time
+from collections.abc import Callable
+from datetime import datetime, timezone
+from typing import Any, Final
+
+from gps_denied_onboard._types.fc import (
+    FcKind,
+    OperatorCommand,
+    OperatorCommandCallback,
+    PortConfig,
+    Severity,
+    Subscription,
+)
+from gps_denied_onboard._types.geo import LatLonAlt
+from gps_denied_onboard._types.pose import EstimatorOutput
+from gps_denied_onboard.components.c8_fc_adapter._covariance_projector import (
+    CovarianceProjector,
+)
+from gps_denied_onboard.components.c8_fc_adapter._subscription import SubscriptionBus
+from gps_denied_onboard.components.c8_fc_adapter.errors import (
+    GcsAdapterConfigError,
+    GcsEmitError,
+)
+from gps_denied_onboard.config import Config
+from gps_denied_onboard.fdr_client.client import FdrClient
+from gps_denied_onboard.fdr_client.records import FdrRecord
+from gps_denied_onboard.logging import get_logger
+
+__all__ = ["QgcTelemetryAdapter"]
+
+
+# Composition-root invocation rate (Hz) for emit_summary; the adapter
+# divides this by ``summary_rate_hz`` to compute the modulo divisor.
+_COMPOSE_ROOT_INVOKE_HZ: Final[float] = 5.0
+_DEFAULT_OPERATOR_COMMAND_TYPES: Final[tuple[str, ...]] = (
+    "PARAM_REQUEST_LIST",
+    "PARAM_REQUEST_READ",
+    "PARAM_SET",
+    "COMMAND_LONG",
+    "COMMAND_INT",
+    "REQUEST_DATA_STREAM",
+    "MISSION_REQUEST",
+    "MISSION_REQUEST_LIST",
+    "MISSION_ITEM",
+    "SET_MODE",
+)
+
+
+def _mav_severity(sev: Severity) -> int:
+    return int(sev.value)
+
+
+def _compute_downsample_modulo(summary_rate_hz: float) -> int:
+    """Return the per-N-call emit modulo for ``summary_rate_hz`` against 5 Hz.
+
+    Examples (the AC tests pin these): 5 Hz -> 1 (no downsample),
+    2 Hz -> 2 (every 2nd call), 1 Hz -> 5 (every 5th), 0.5 Hz -> 10.
+    Sub-1 Hz floors don't round to zero because we use ``round`` with
+    a minimum of 1 below.
+    """
+    if summary_rate_hz <= 0.0:
+        raise GcsAdapterConfigError(f"summary_rate_hz must be > 0; got {summary_rate_hz}")
+    ratio = _COMPOSE_ROOT_INVOKE_HZ / summary_rate_hz
+    return max(1, round(ratio))
+
+
+class QgcTelemetryAdapter:
+    """Concrete :class:`GcsAdapter` strategy.
+
+    Threading:
+    - Outbound (``emit_summary`` / ``emit_status_text``) is bound to a
+      single composition-root thread; emitting from a second thread
+      raises :class:`RuntimeError` (Invariant 8 mirror).
+    - Inbound operator-command dispatch fires on the message-handler
+      thread (pymavlink's recv loop). Subscriber callbacks are
+      invoked synchronously; the bus isolates crashes per the C8
+      inbound pattern.
+    """
+
+    def __init__(
+        self,
+        *,
+        config: Config,
+        wgs_converter: Any,
+        covariance_projector: CovarianceProjector,
+        fdr_client: FdrClient,
+        clock: Callable[[], float] = time.monotonic,
+        connect_factory: Callable[[str, int], Any] | None = None,
+    ) -> None:
+        self._config = config
+        self._wgs_converter = wgs_converter
+        self._cov_projector = covariance_projector
+        self._fdr_client = fdr_client
+        self._clock = clock
+        self._connect_factory = connect_factory
+        self._log = get_logger("c8_gcs_adapter.qgc")
+        # The modulo divisor — computed once at construction so unit
+        # tests can pin a 5 Hz call → N-frame relationship.
+        self._downsample_modulo: int = _compute_downsample_modulo(float(config.gcs.summary_rate_hz))
+        # Wire state ------------------------------------------------------
+        self._connection: Any = None
+        self._opened = False
+        self._invocation_count = 0
+        self._frame_seq = 0
+        self._first_emit_logged = False
+        self._open_emit_thread_ident: int | None = None
+        self._operator_bus = SubscriptionBus()
+        self._operator_handler_attached = False
+        self._operator_lock = threading.Lock()
+
+    # ------------------------------------------------------------------
+    # GcsAdapter Protocol implementation
+
+    def open(self, port: PortConfig) -> None:
+        if self._opened:
+            raise GcsAdapterConfigError("QgcTelemetryAdapter already opened")
+        if port.fc_kind is not FcKind.GCS_QGC:
+            raise GcsAdapterConfigError(
+                f"QgcTelemetryAdapter requires FcKind.GCS_QGC; got {port.fc_kind!r}"
+            )
+        try:
+            self._connection = self._connect(port)
+        except Exception as exc:
+            raise GcsAdapterConfigError(f"QGC MAVLink connect failed: {exc!r}") from exc
+        self._opened = True
+        self._invocation_count = 0
+        self._frame_seq = 0
+        self._first_emit_logged = False
+        self._open_emit_thread_ident = None
+
+    def close(self) -> None:
+        if not self._opened:
+            return
+        try:
+            if self._connection is not None and hasattr(self._connection, "close"):
+                self._connection.close()
+        finally:
+            self._opened = False
+            self._connection = None
+            self._open_emit_thread_ident = None
+
+    def emit_summary(self, output: EstimatorOutput) -> None:
+        if not self._opened or self._connection is None:
+            raise GcsEmitError("adapter not opened")
+        self._enforce_single_writer()
+        self._invocation_count += 1
+        if (self._invocation_count % self._downsample_modulo) != 0:
+            return  # downsampled — skip this call
+        wgs = self._extract_wgs84(output)
+        horiz_accuracy_m = self._cov_projector.to_ardupilot_horiz_accuracy_m(output)
+        self._frame_seq += 1
+        try:
+            self._connection.mav.global_position_int_send(
+                int(self._clock_ms_boot()),
+                int(wgs.lat_deg * 1e7),
+                int(wgs.lon_deg * 1e7),
+                int(wgs.alt_m * 1000.0),  # WGS84 alt in mm
+                int(wgs.alt_m * 1000.0),  # relative alt; placeholder
+                0,
+                0,
+                0,  # vx, vy, vz (cm/s) — 0 for summary
+                0,  # hdg (cdeg); 0 = unset
+            )
+            self._connection.mav.named_value_float_send(
+                int(self._clock_ms_boot()),
+                b"horiz_m",
+                float(horiz_accuracy_m),
+            )
+        except Exception as exc:
+            self._log.error(
+                f"c8.gcs.summary_emit_failed: {exc!r}",
+                extra={
+                    "kind": "c8.gcs.summary_emit_failed",
+                    "kv": {"error": repr(exc), "frame_seq": self._frame_seq},
+                },
+            )
+            raise GcsEmitError(f"GCS summary emit failed: {exc!r}") from exc
+        if not self._first_emit_logged:
+            self._first_emit_logged = True
+            self._log.info(
+                "c8.gcs.first_summary_emit",
+                extra={
+                    "kind": "c8.gcs.first_summary_emit",
+                    "kv": {
+                        "frame_seq": self._frame_seq,
+                        "downsample_modulo": self._downsample_modulo,
+                    },
+                },
+            )
+        self._log.debug(
+            "c8.gcs.summary_emit",
+            extra={
+                "kind": "c8.gcs.summary_emit",
+                "kv": {
+                    "seq": self._frame_seq,
+                    "lat": wgs.lat_deg,
+                    "lon": wgs.lon_deg,
+                    "horiz_accuracy_m": horiz_accuracy_m,
+                    "source_label": output.source_label,
+                },
+            },
+        )
+
+    def subscribe_operator_commands(self, callback: OperatorCommandCallback) -> Subscription:
+        handle = self._operator_bus.subscribe(callback)
+        self._ensure_operator_handler_attached()
+        return handle
+
+    def emit_status_text(self, msg: str, severity: Severity) -> None:
+        if not self._opened or self._connection is None:
+            raise GcsEmitError("adapter not opened")
+        self._enforce_single_writer()
+        try:
+            text = msg.encode("utf-8")[:50]
+            self._connection.mav.statustext_send(_mav_severity(severity), text)
+        except Exception as exc:
+            self._log.debug(
+                f"c8.gcs.statustext_failed: {exc!r}",
+                extra={
+                    "kind": "c8.gcs.statustext_failed",
+                    "kv": {"error": repr(exc)},
+                },
+            )
+
+    # ------------------------------------------------------------------
+    # Internals
+
+    def _enforce_single_writer(self) -> None:
+        cur = threading.get_ident()
+        if self._open_emit_thread_ident is None:
+            self._open_emit_thread_ident = cur
+            return
+        if self._open_emit_thread_ident != cur:
+            raise RuntimeError(
+                "QgcTelemetryAdapter outbound is single-writer; "
+                f"first thread={self._open_emit_thread_ident}, this thread={cur}"
+            )
+
+    def _connect(self, port: PortConfig) -> Any:
+        if self._connect_factory is not None:
+            return self._connect_factory(port.device, port.baud)
+        from pymavlink import mavutil  # lazy import per ADR-002
+
+        return mavutil.mavlink_connection(
+            port.device,
+            baud=port.baud,
+            dialect="common",
+            mavlink_version="2.0",
+        )
+
+    def _ensure_operator_handler_attached(self) -> None:
+        with self._operator_lock:
+            if self._operator_handler_attached or self._connection is None:
+                return
+            register = getattr(self._connection, "message_hooks", None)
+            if register is None or not isinstance(register, list):
+                # The injected stub may expose a `register_message_hook`
+                # callable; honour that too for test ergonomics.
+                hook_register = getattr(self._connection, "register_message_hook", None)
+                if callable(hook_register):
+                    hook_register(self._on_inbound_message)
+                else:
+                    return
+            else:
+                register.append(self._on_inbound_message)
+            self._operator_handler_attached = True
+
+    def _on_inbound_message(self, *args: Any) -> None:
+        """Pymavlink message-hook entrypoint.
+
+        pymavlink calls hooks with ``(self, conn, msg)`` for instance
+        hooks or ``(conn, msg)`` for free-function hooks; the message
+        is always the last positional argument.
+        """
+        if not args:
+            return
+        msg = args[-1]
+        try:
+            msg_type = msg.get_type() if hasattr(msg, "get_type") else str(type(msg).__name__)
+        except Exception:
+            return
+        if msg_type not in _DEFAULT_OPERATOR_COMMAND_TYPES:
+            return
+        cmd = self._translate_to_operator_command(msg_type, msg)
+        self._operator_bus.dispatch(cmd)
+        self._record_operator_command_fdr(cmd, msg)
+
+    def _translate_to_operator_command(self, msg_type: str, msg: Any) -> OperatorCommand:
+        payload: dict[str, str | int | float | bool] = {}
+        for attr in (
+            "param_id",
+            "param_value",
+            "command",
+            "result",
+            "target_system",
+            "target_component",
+        ):
+            if hasattr(msg, attr):
+                value = getattr(msg, attr)
+                if isinstance(value, (str, int, float, bool)):
+                    payload[attr] = value
+                elif isinstance(value, bytes):
+                    try:
+                        payload[attr] = value.decode("utf-8", errors="replace")
+                    except Exception:
+                        payload[attr] = value.hex()
+        return OperatorCommand(
+            command=msg_type,
+            payload=payload,
+            received_at=time.monotonic_ns(),
+        )
+
+    def _record_operator_command_fdr(self, cmd: OperatorCommand, msg: Any) -> None:
+        record = FdrRecord(
+            schema_version=1,
+            ts=datetime.now(tz=timezone.utc).isoformat(),
+            producer_id="c8_gcs_adapter",
+            kind="log",
+            payload={
+                "level": "INFO",
+                "component": "c8_gcs_adapter",
+                "kind": "c8.gcs.operator_command",
+                "msg": "c8.gcs.operator_command",
+                "kv": {
+                    "command": cmd.command,
+                    "payload": cmd.payload,
+                    "source_system": int(getattr(msg, "get_srcSystem", lambda: 0)() or 0),
+                },
+            },
+        )
+        try:
+            self._fdr_client.enqueue(record)
+        except Exception as exc:
+            self._log.debug(
+                f"c8.gcs.operator_command_fdr_enqueue_failed: {exc!r}",
+                extra={
+                    "kind": "c8.gcs.operator_command_fdr_enqueue_failed",
+                    "kv": {"error": repr(exc)},
+                },
+            )
+
+    def _extract_wgs84(self, output: EstimatorOutput) -> LatLonAlt:
+        wgs = output.extras.get("wgs84") if output.extras else None
+        if not isinstance(wgs, LatLonAlt):
+            raise GcsEmitError(
+                "EstimatorOutput.extras['wgs84'] missing or not a LatLonAlt; "
+                "composition root must inject the ENU->WGS84 enricher"
+            )
+        return wgs
+
+    def _clock_ms_boot(self) -> int:
+        return int(self._clock() * 1_000)
@@ -54,6 +54,7 @@ from gps_denied_onboard.components.c8_fc_adapter.errors import (
    FcEmitError,
    FcOpenError,
    SigningHandshakeError,
+    SourceSetSwitchError,
 )
 from gps_denied_onboard.config import Config
 from gps_denied_onboard.fdr_client.client import FdrClient
@@ -67,6 +68,10 @@ _GPS_FIX_TYPE_3D: Final[int] = 3
 _NAMED_VALUE_FLOAT_NAME: Final[str] = "src_lbl"
 _SIGNING_KEY_LEN: Final[int] = 32
 _BUILD_DEV_STATIC_KEY_ENV: Final[str] = "BUILD_DEV_STATIC_KEY"
+# ArduPilot-specific command (dialect: ardupilotmega).
+_MAV_CMD_SET_EKF_SOURCE_SET: Final[int] = 42007
+_MAV_RESULT_ACCEPTED: Final[int] = 0
+_SWITCH_RATE_LIMIT_S: Final[float] = 1.0


 # Maps Severity enum to MAVLink statustext severity numeric value.
@@ -110,6 +115,9 @@ class PymavlinkArdupilotAdapter:
        self._first_emit_logged = False
        self._open_emit_thread_ident: int | None = None
        self._signing_failure_logged_at_count = 0
+        # D-C8-2 source-set switch state (AZ-396).
+        self._last_switch_attempt_ns: int = 0
+        self._last_switch_succeeded: bool = False
        # Inbound bus + decoder (lazily constructed inside ``open``).
        self._bus = SubscriptionBus()
        self._inbound: PymavlinkInboundDecoder | None = None
@@ -291,7 +299,85 @@ class PymavlinkArdupilotAdapter:
        self._send_statustext_internal(msg, severity)

    def request_source_set_switch(self) -> None:
-        raise NotImplementedError("Owned by source-set task; install AZ-396 to enable")
+        """D-C8-2 source-set switch (AZ-396 / AC-NEW-2).
+
+        Sends ``MAV_CMD_SET_EKF_SOURCE_SET`` (ardupilotmega cmd 42007)
+        with ``param1 = config.fc.spoof_recovery_source_set`` and waits
+        up to ``config.fc.source_set_switch_timeout_ms`` for the FC's
+        ``COMMAND_ACK``. Idempotence per Invariant 11: a second call
+        within ``_SWITCH_RATE_LIMIT_S`` of the previous attempt is
+        no-op'd; a call after a successful switch logs INFO + STATUSTEXT
+        but does NOT re-issue.
+        """
+        if not self._opened or self._connection is None:
+            raise FcEmitError("adapter not opened")
+        self._enforce_single_writer()
+        now_ns = time.monotonic_ns()
+        if self._last_switch_attempt_ns:
+            elapsed_s = (now_ns - self._last_switch_attempt_ns) / 1_000_000_000
+            if elapsed_s < _SWITCH_RATE_LIMIT_S:
+                self._log.info(
+                    "c8.ap.source_set_switch_rate_limited",
+                    extra={
+                        "kind": "c8.ap.source_set_switch_rate_limited",
+                        "kv": {"elapsed_s": round(elapsed_s, 3)},
+                    },
+                )
+                return
+            if self._last_switch_succeeded:
+                self._log.info(
+                    "c8.ap.source_set_switch_already_active",
+                    extra={"kind": "c8.ap.source_set_switch_already_active", "kv": {}},
+                )
+                self._send_statustext_internal("src-set already active", Severity.INFO)
+                return
+        self._last_switch_attempt_ns = now_ns
+        source_set = int(self._config.fc.spoof_recovery_source_set)
+        timeout_ms = int(self._config.fc.source_set_switch_timeout_ms)
+        try:
+            self._connection.mav.command_long_send(
+                getattr(self._connection, "target_system", 1),
+                getattr(self._connection, "target_component", 1),
+                _MAV_CMD_SET_EKF_SOURCE_SET,
+                0,
+                float(source_set),
+                0.0,
+                0.0,
+                0.0,
+                0.0,
+                0.0,
+                0.0,
+            )
+        except Exception as exc:
+            self._handle_source_set_switch_failure(
+                reason=f"command_long_send failed: {exc!r}", source_set=source_set
+            )
+            raise SourceSetSwitchError(f"MAV_CMD_SET_EKF_SOURCE_SET send failed: {exc!r}") from exc
+        ack = self._wait_for_command_ack(_MAV_CMD_SET_EKF_SOURCE_SET, timeout_ms=timeout_ms)
+        if ack is None:
+            self._handle_source_set_switch_failure(
+                reason=f"ACK timeout after {timeout_ms}ms", source_set=source_set
+            )
+            raise SourceSetSwitchError(f"ACK timeout after {timeout_ms}ms")
+        result = int(getattr(ack, "result", -1))
+        if result != _MAV_RESULT_ACCEPTED:
+            self._handle_source_set_switch_failure(
+                reason=f"ACK result={result}", source_set=source_set
+            )
+            raise SourceSetSwitchError(f"MAV_CMD_SET_EKF_SOURCE_SET rejected: result={result}")
+        self._last_switch_succeeded = True
+        self._log.info(
+            "c8.ap.source_set_switch_executed",
+            extra={
+                "kind": "c8.ap.source_set_switch_executed",
+                "kv": {"source_set": source_set},
+            },
+        )
+        self._fdr_signing_event(
+            kind="c8.ap.source_set_switch_executed",
+            kv={"source_set": source_set, "flight_id": self._flight_id},
+        )
+        self._send_statustext_internal(f"src-set switched to {source_set}", Severity.INFO)

    def current_flight_state(self) -> FlightStateSignal:
        if self._inbound is None:
@@ -450,6 +536,57 @@ class PymavlinkArdupilotAdapter:
            },
        )

+    def _wait_for_command_ack(self, command_id: int, *, timeout_ms: int) -> Any | None:
+        """Wait up to ``timeout_ms`` for a `COMMAND_ACK` for ``command_id``.
+
+        Returns the ACK message on match, or ``None`` on timeout. Other
+        COMMAND_ACK messages (for unrelated commands) are ignored.
+        """
+        deadline = self._clock() + (timeout_ms / 1000.0)
+        while True:
+            remaining = deadline - self._clock()
+            if remaining <= 0:
+                return None
+            try:
+                msg = self._connection.recv_match(
+                    type="COMMAND_ACK", blocking=True, timeout=remaining
+                )
+            except Exception as exc:
+                self._log.debug(
+                    f"c8.ap.recv_match_failed: {exc!r}",
+                    extra={
+                        "kind": "c8.ap.recv_match_failed",
+                        "kv": {"error": repr(exc)},
+                    },
+                )
+                return None
+            if msg is None:
+                return None
+            if int(getattr(msg, "command", -1)) == command_id:
+                return msg
+
+    def _handle_source_set_switch_failure(self, *, reason: str, source_set: int) -> None:
+        self._last_switch_succeeded = False
+        self._log.error(
+            f"c8.ap.source_set_switch_failed: {reason}",
+            extra={
+                "kind": "c8.ap.source_set_switch_failed",
+                "kv": {"reason": reason, "source_set": source_set},
+            },
+        )
+        self._fdr_signing_event(
+            kind="c8.ap.source_set_switch_failed",
+            kv={
+                "reason": reason,
+                "source_set": source_set,
+                "flight_id": self._flight_id,
+            },
+        )
+        try:
+            self._send_statustext_internal(f"src-set switch failed: {reason}", Severity.ERROR)
+        except Exception:
+            pass
+
    def _extract_wgs84(self, output: EstimatorOutput) -> LatLonAlt:
        """Pull the WGS84 fix the composition root pre-attached.

@@ -58,6 +58,8 @@ ENV_KEY_MAP: Final[dict[str, tuple[str, str]]] = {
    "FC_SIGNING_KEY_SOURCE": ("fc", "signing_key_source"),
    "FC_DEV_STATIC_SIGNING_KEY": ("fc", "dev_static_signing_key"),
    "FC_SIGNING_FAILURE_THRESHOLD": ("fc", "signing_failure_threshold"),
+    "FC_SPOOF_RECOVERY_SOURCE_SET": ("fc", "spoof_recovery_source_set"),
+    "FC_SOURCE_SET_SWITCH_TIMEOUT_MS": ("fc", "source_set_switch_timeout_ms"),
    "GCS_ADAPTER": ("gcs", "adapter"),
    "GCS_PORT_DEVICE": ("gcs", "port_device"),
    "GCS_PORT_BAUD": ("gcs", "port_baud"),
@@ -101,6 +103,8 @@ _FIELD_COERCIONS: Final[dict[str, type]] = {
    "signing_key_source": str,
    "dev_static_signing_key": str,
    "signing_failure_threshold": int,
+    "spoof_recovery_source_set": int,
+    "source_set_switch_timeout_ms": int,
    "summary_rate_hz": float,
 }

@@ -209,6 +209,8 @@ class FcConfig:
    signing_key_source: str = "ephemeral_per_flight"
    dev_static_signing_key: str = ""
    signing_failure_threshold: int = 3
+    spoof_recovery_source_set: int = 1
+    source_set_switch_timeout_ms: int = 1500

    def __post_init__(self) -> None:
        if self.adapter not in KNOWN_FC_STRATEGIES:
@@ -238,6 +240,16 @@ class FcConfig:
                "FcConfig.signing_failure_threshold must be >= 1; got "
                f"{self.signing_failure_threshold}"
            )
+        if self.spoof_recovery_source_set < 0:
+            raise ConfigError(
+                "FcConfig.spoof_recovery_source_set must be >= 0; got "
+                f"{self.spoof_recovery_source_set}"
+            )
+        if self.source_set_switch_timeout_ms < 100:
+            raise ConfigError(
+                "FcConfig.source_set_switch_timeout_ms must be >= 100 ms; got "
+                f"{self.source_set_switch_timeout_ms}"
+            )


@dataclass(frozen=True)
@@ -246,7 +258,7 @@ class GcsConfig:

    ``adapter`` selects one of :data:`KNOWN_GCS_STRATEGIES`.
    ``summary_rate_hz`` is the per-emitter downsample target
-    (Invariant 12; default 2 Hz; range [1, 2]).
+    (Invariant 12; default 2 Hz; range [0.5, 5.0] per AZ-397 AC-10).
    """

    adapter: str = "qgc_mavlink"
@@ -259,9 +271,9 @@ class GcsConfig:
            raise ConfigError(
                f"GcsConfig.adapter={self.adapter!r} not in {sorted(KNOWN_GCS_STRATEGIES)}"
            )
-        if not (1.0 <= self.summary_rate_hz <= 2.0):
+        if not (0.5 <= self.summary_rate_hz <= 5.0):
            raise ConfigError(
-                f"GcsConfig.summary_rate_hz must be in [1.0, 2.0]; got {self.summary_rate_hz}"
+                f"GcsConfig.summary_rate_hz must be in [0.5, 5.0]; got {self.summary_rate_hz}"
            )


@@ -36,6 +36,10 @@ from gps_denied_onboard.runtime_root.fc_factory import (
    register_fc_adapter,
    register_gcs_adapter,
 )
+from gps_denied_onboard.runtime_root.spoof_recovery_sink import (
+    SpoofRecoveryPublisher,
+    SpoofRecoverySink,
+)

 if TYPE_CHECKING:
    from gps_denied_onboard.components.c13_fdr.headers import FlightHeader
@@ -49,6 +53,8 @@ __all__ = [
    "OperatorRoot",
    "OutboundThreadAlreadyBoundError",
    "RuntimeRoot",
+    "SpoofRecoveryPublisher",
+    "SpoofRecoverySink",
    "StrategyNotLinkedError",
    "StrategyTier",
    "TakeoffResult",
@@ -0,0 +1,139 @@
+"""Spoof-recovery signal sink (AZ-396 / E-C8 runtime-root wiring).
+
+C5's spoof-promotion gate (AZ-385) publishes a ``spoof_promotion_recovered``
+signal when a previously-spoofed FC GPS source clears the recovery
+window. The runtime root forwards that signal to the C8 AP adapter's
+:meth:`request_source_set_switch` on the OUTBOUND emit thread so the
+single-writer invariant (Invariant 8) is preserved.
+
+This module owns ONLY the wiring side; the publisher side lives in
+C5 (AZ-385 — not yet landed). The sink exposes a Protocol the
+runtime root binds at composition-root build time:
+
+- :class:`SpoofRecoveryPublisher` — Protocol the C5 gate implements.
+- :class:`SpoofRecoverySink` — registers itself with a publisher and
+  fires ``request_source_set_switch`` on the C8 adapter.
+
+Single-writer enforcement: the sink ALWAYS dispatches the C8 adapter
+call on a single bound thread (the C8 outbound thread). It uses a
+thread-safe queue so the C5 thread can publish without blocking on
+the C8 wire.
+"""
+
+from __future__ import annotations
+
+import queue
+import threading
+from typing import Protocol
+
+from gps_denied_onboard.components.c8_fc_adapter.errors import (
+    FcAdapterError,
+    SourceSetSwitchError,
+)
+from gps_denied_onboard.components.c8_fc_adapter.interface import FcAdapter
+from gps_denied_onboard.logging import get_logger
+
+__all__ = [
+    "SpoofRecoveryPublisher",
+    "SpoofRecoverySink",
+]
+
+
+class SpoofRecoveryPublisher(Protocol):
+    """Protocol C5 (AZ-385) implements to surface the recovery signal."""
+
+    def subscribe_spoof_promotion_recovered(self, callback: _Callback) -> object:
+        """Register ``callback`` to be invoked when the gate recovers.
+
+        Returns a handle whose ``cancel()`` method removes the subscription.
+        """
+
+
+class _Callback(Protocol):
+    def __call__(self) -> None: ...
+
+
+class SpoofRecoverySink:
+    """Dispatches C5 spoof-recovery signals to the AP adapter outbound thread.
+
+    Usage from the composition root::
+
+        sink = SpoofRecoverySink(fc_adapter)
+        sink.start()
+        publisher.subscribe_spoof_promotion_recovered(sink.publish)
+        # ... at shutdown ...
+        sink.stop()
+    """
+
+    def __init__(self, fc_adapter: FcAdapter) -> None:
+        self._fc = fc_adapter
+        self._queue: queue.Queue[None] = queue.Queue(maxsize=16)
+        self._stop = threading.Event()
+        self._thread: threading.Thread | None = None
+        self._log = get_logger("runtime_root.spoof_recovery_sink")
+
+    def start(self) -> None:
+        """Start the dispatch thread; idempotent."""
+        if self._thread is not None and self._thread.is_alive():
+            return
+        self._stop.clear()
+        self._thread = threading.Thread(
+            target=self._run, name="c8.spoof_recovery_sink", daemon=True
+        )
+        self._thread.start()
+
+    def stop(self, *, join_timeout_s: float = 1.0) -> None:
+        """Signal the dispatch thread to exit and join."""
+        self._stop.set()
+        # Wake the queue.get(...) blocker without leaking a real signal.
+        try:
+            self._queue.put_nowait(None)
+        except queue.Full:
+            pass
+        if self._thread is not None:
+            self._thread.join(timeout=join_timeout_s)
+            self._thread = None
+
+    def publish(self) -> None:
+        """Invoked by the C5 publisher thread; enqueues a switch request."""
+        try:
+            self._queue.put_nowait(None)
+        except queue.Full:
+            # Bounded queue: 16 pending switches is far more than the
+            # recovery gate can produce; if we ever hit this, something
+            # upstream is flooding. Emit a WARN and drop — the C8
+            # idempotence gate (Invariant 11) would suppress them anyway.
+            self._log.warning(
+                "c8.spoof_recovery_sink_queue_full",
+                extra={"kind": "c8.spoof_recovery_sink_queue_full", "kv": {}},
+            )
+
+    def _run(self) -> None:
+        while not self._stop.is_set():
+            try:
+                _ = self._queue.get(timeout=0.5)
+            except queue.Empty:
+                continue
+            if self._stop.is_set():
+                return
+            try:
+                self._fc.request_source_set_switch()
+            except SourceSetSwitchError as exc:
+                # Per spec § 5 error-handling: ERROR log + STATUSTEXT
+                # already happened inside the adapter; we re-log at
+                # DEBUG here so the sink-level audit shows the catch.
+                self._log.debug(
+                    f"c8.spoof_recovery_sink_switch_failed: {exc!r}",
+                    extra={
+                        "kind": "c8.spoof_recovery_sink_switch_failed",
+                        "kv": {"error": repr(exc)},
+                    },
+                )
+            except FcAdapterError as exc:
+                self._log.warning(
+                    f"c8.spoof_recovery_sink_adapter_error: {exc!r}",
+                    extra={
+                        "kind": "c8.spoof_recovery_sink_adapter_error",
+                        "kv": {"error": repr(exc)},
+                    },
+                )
@@ -229,7 +229,7 @@ def test_ac2_fc_telemetry_frame_dto_frozen() -> None:

 def test_ac3_fc_kind_has_two_members() -> None:
    # Assert
-    assert {m.name for m in FcKind} == {"ARDUPILOT_PLANE", "INAV"}
+    assert {m.name for m in FcKind} == {"ARDUPILOT_PLANE", "INAV", "GCS_QGC"}


 def test_ac3_flight_state_has_five_members() -> None:
@@ -505,9 +505,11 @@ def test_signing_key_source_unknown_value_rejected() -> None:


 def test_gcs_summary_rate_out_of_range_rejected() -> None:
+    # AZ-397 widened the valid range to [0.5, 5.0] (AC-10); the boundary
+    # cases below now fall OUTSIDE the new range.
    # Act + Assert — too high
    with pytest.raises(ConfigError, match=r"summary_rate_hz"):
-        GcsConfig(summary_rate_hz=5.0)
+        GcsConfig(summary_rate_hz=5.1)
    # Too low
    with pytest.raises(ConfigError, match=r"summary_rate_hz"):
-        GcsConfig(summary_rate_hz=0.5)
+        GcsConfig(summary_rate_hz=0.4)
@@ -297,12 +297,17 @@ def test_ac8_open_without_signing_key_succeeds(conn: _ConnStub, tmp_path) -> Non


 # ----------------------------------------------------------------------
-# AC-9: source-set switch raises NotImplementedError
+# AC-9: source-set switch is wired (AZ-396 replaced AZ-393's placeholder)
+#
+# AZ-393's original AC-9 asserted `request_source_set_switch()` raises
+# `NotImplementedError`; AZ-396 (batch 11) replaced that placeholder
+# with the real body. The AZ-396 AC tests cover the new behaviour;
+# the AZ-393 surface is now exercised by those tests rather than this
+# one. The check left here verifies the method is present and callable.


-def test_ac9_source_set_switch_not_implemented(adapter: PymavlinkArdupilotAdapter) -> None:
-    with pytest.raises(NotImplementedError, match="AZ-396"):
-        adapter.request_source_set_switch()
+def test_ac9_source_set_switch_method_callable(adapter: PymavlinkArdupilotAdapter) -> None:
+    assert callable(adapter.request_source_set_switch)


 # ----------------------------------------------------------------------
@@ -0,0 +1,370 @@
+"""AZ-396 — D-C8-2 source-set switch AC tests."""
+
+from __future__ import annotations
+
+import logging
+import threading
+import time
+from collections.abc import Iterable
+from typing import Any
+from unittest import mock
+
+import pytest
+
+from gps_denied_onboard._types.fc import FcKind, PortConfig, Severity
+from gps_denied_onboard.components.c8_fc_adapter._covariance_projector import (
+    CovarianceProjector,
+)
+from gps_denied_onboard.components.c8_fc_adapter.errors import SourceSetSwitchError
+from gps_denied_onboard.components.c8_fc_adapter.pymavlink_ardupilot_adapter import (
+    PymavlinkArdupilotAdapter,
+)
+from gps_denied_onboard.config import load_config
+from gps_denied_onboard.runtime_root.spoof_recovery_sink import SpoofRecoverySink
+
+# AC-1 / AC-2 / AC-3: pymavlink ardupilotmega command id for SET_EKF_SOURCE_SET.
+_CMD_SET_EKF_SOURCE_SET = 42007
+_MAV_RESULT_ACCEPTED = 0
+_MAV_RESULT_FAILED = 4
+
+
+class _AckMsg:
+    def __init__(self, command: int, result: int) -> None:
+        self.command = command
+        self.result = result
+
+
+class _MavStub:
+    def __init__(self) -> None:
+        self.command_long_calls: list[tuple[int, ...]] = []
+        self.statustext_calls: list[tuple[int, bytes]] = []
+        self.named_value_float_calls: list[tuple[Any, ...]] = []
+        self.gps_input_calls: list[tuple[Any, ...]] = []
+
+    def command_long_send(
+        self,
+        target_system: int,
+        target_component: int,
+        command: int,
+        confirmation: int,
+        p1: float,
+        p2: float,
+        p3: float,
+        p4: float,
+        p5: float,
+        p6: float,
+        p7: float,
+    ) -> None:
+        self.command_long_calls.append((target_system, target_component, command, confirmation, p1))
+
+    def statustext_send(self, severity: int, text: bytes) -> None:
+        self.statustext_calls.append((severity, text))
+
+    def named_value_float_send(self, time_boot_ms: int, name: bytes, value: float) -> None:
+        self.named_value_float_calls.append((time_boot_ms, name, value))
+
+    def gps_input_send(self, *args: Any) -> None:
+        self.gps_input_calls.append(args)
+
+
+class _ConnStub:
+    def __init__(self, ack_queue: Iterable[_AckMsg] | None = None) -> None:
+        self.mav = _MavStub()
+        self.target_system = 1
+        self.target_component = 1
+        self._ack_queue = list(ack_queue or [])
+        self.closed = False
+
+    def recv_match(self, *, type: str, blocking: bool, timeout: float | None) -> Any:
+        # Real pymavlink filters by ``type``; the inbound decoder thread
+        # calls recv_match without a type filter (None), the outbound
+        # source-set switch calls with type="COMMAND_ACK". Honour that
+        # so the inbound loop does not eat our ACK.
+        if type != "COMMAND_ACK":
+            return None
+        if not self._ack_queue:
+            return None
+        return self._ack_queue.pop(0)
+
+    def setup_signing(self, key: bytes) -> None:
+        pass
+
+    def close(self) -> None:
+        self.closed = True
+
+
+def _ap_config(
+    *,
+    source_set: int = 1,
+    timeout_ms: int = 1500,
+) -> Any:
+    env = {
+        "FC_ADAPTER": "ardupilot_plane",
+        "FC_PORT_DEVICE": "/dev/null",
+        "FC_PORT_BAUD": "921600",
+        "FC_SIGNING_KEY_SOURCE": "none",
+        "FC_SPOOF_RECOVERY_SOURCE_SET": str(source_set),
+        "FC_SOURCE_SET_SWITCH_TIMEOUT_MS": str(timeout_ms),
+    }
+    return load_config(env=env, paths=(), require_env=False)
+
+
+def _make_adapter(conn: _ConnStub, cfg: Any) -> PymavlinkArdupilotAdapter:
+    fdr = mock.MagicMock()
+    a = PymavlinkArdupilotAdapter(
+        config=cfg,
+        wgs_converter=mock.MagicMock(),
+        covariance_projector=CovarianceProjector(fdr_client=fdr),
+        fdr_client=fdr,
+        flight_id="flt-az396",
+        connect_factory=lambda device, baud: conn,
+    )
+    port = PortConfig(fc_kind=FcKind.ARDUPILOT_PLANE, device="/dev/null", baud=921600)
+    a.open(port, signing_key=None)
+    return a
+
+
+# ----------------------------------------------------------------------
+# AC-1: ACK success path
+
+
+def test_ac1_ack_success(caplog: pytest.LogCaptureFixture) -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_ACCEPTED)])
+    a = _make_adapter(conn, _ap_config(source_set=1))
+    try:
+        with caplog.at_level(logging.INFO):
+            a.request_source_set_switch()
+        assert len(conn.mav.command_long_calls) == 1
+        _, _, cmd, _, p1 = conn.mav.command_long_calls[0]
+        assert cmd == _CMD_SET_EKF_SOURCE_SET
+        assert p1 == 1.0
+        assert any(
+            getattr(r, "kind", None) == "c8.ap.source_set_switch_executed" for r in caplog.records
+        )
+        assert any(sev == int(Severity.INFO.value) for sev, _ in conn.mav.statustext_calls)
+        assert any(
+            call.args[0].payload.get("kind") == "c8.ap.source_set_switch_executed"
+            for call in a._fdr_client.enqueue.mock_calls  # type: ignore[attr-defined]
+        )
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-2: non-success ACK raises
+
+
+def test_ac2_non_success_ack_raises(caplog: pytest.LogCaptureFixture) -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_FAILED)])
+    a = _make_adapter(conn, _ap_config())
+    try:
+        with caplog.at_level(logging.ERROR), pytest.raises(SourceSetSwitchError, match="result=4"):
+            a.request_source_set_switch()
+        assert any(
+            getattr(r, "kind", None) == "c8.ap.source_set_switch_failed" for r in caplog.records
+        )
+        assert any(sev == int(Severity.ERROR.value) for sev, _ in conn.mav.statustext_calls)
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-3: ACK timeout raises
+
+
+def test_ac3_ack_timeout_raises(caplog: pytest.LogCaptureFixture) -> None:
+    conn = _ConnStub(ack_queue=[])  # never ACK
+    a = _make_adapter(conn, _ap_config(timeout_ms=200))
+    try:
+        with (
+            caplog.at_level(logging.ERROR),
+            pytest.raises(SourceSetSwitchError, match="timeout after 200ms"),
+        ):
+            a.request_source_set_switch()
+        assert any(
+            getattr(r, "kind", None) == "c8.ap.source_set_switch_failed" for r in caplog.records
+        )
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-4: configurable timeout (AC-3 already exercises a non-default value)
+
+
+def test_ac4_configurable_timeout_uses_config_value() -> None:
+    conn = _ConnStub(ack_queue=[])
+    cfg = _ap_config(timeout_ms=500)
+    a = _make_adapter(conn, cfg)
+    try:
+        with pytest.raises(SourceSetSwitchError, match="timeout after 500ms"):
+            a.request_source_set_switch()
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-5: idempotence within 1 s — second call no-op'd
+
+
+def test_ac5_idempotence_within_1s_rate_limited(caplog: pytest.LogCaptureFixture) -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_FAILED)])
+    a = _make_adapter(conn, _ap_config())
+    try:
+        with pytest.raises(SourceSetSwitchError):
+            a.request_source_set_switch()
+        with caplog.at_level(logging.INFO):
+            a.request_source_set_switch()
+        # only one command_long_send hit the wire
+        assert len(conn.mav.command_long_calls) == 1
+        assert any(
+            getattr(r, "kind", None) == "c8.ap.source_set_switch_rate_limited"
+            for r in caplog.records
+        )
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-6: idempotence after successful switch — second call after >1 s logs
+# but does NOT re-emit
+
+
+def test_ac6_idempotence_after_success_no_reissue(caplog: pytest.LogCaptureFixture) -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_ACCEPTED)])
+    a = _make_adapter(conn, _ap_config())
+    try:
+        a.request_source_set_switch()
+        # advance the monotonic clock past the 1 s rate-limit by mutating
+        # the stored timestamp (we control the adapter under test).
+        a._last_switch_attempt_ns -= 2_000_000_000  # type: ignore[attr-defined]
+        with caplog.at_level(logging.INFO):
+            a.request_source_set_switch()
+        assert len(conn.mav.command_long_calls) == 1  # never re-issued
+        assert any(
+            getattr(r, "kind", None) == "c8.ap.source_set_switch_already_active"
+            for r in caplog.records
+        )
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-7: SpoofRecoverySink invokes request_source_set_switch on adapter
+
+
+def test_ac7_spoof_recovery_sink_triggers_switch() -> None:
+    mock_adapter = mock.MagicMock()
+    sink = SpoofRecoverySink(mock_adapter)
+    sink.start()
+    try:
+        sink.publish()
+        # Wait briefly for the dispatch thread to process.
+        for _ in range(20):
+            if mock_adapter.request_source_set_switch.call_count >= 1:
+                break
+            time.sleep(0.05)
+        assert mock_adapter.request_source_set_switch.call_count == 1
+    finally:
+        sink.stop()
+
+
+def test_ac7_spoof_recovery_sink_isolates_errors() -> None:
+    mock_adapter = mock.MagicMock()
+    mock_adapter.request_source_set_switch.side_effect = SourceSetSwitchError("ACK timeout")
+    sink = SpoofRecoverySink(mock_adapter)
+    sink.start()
+    try:
+        sink.publish()
+        # Sink must not crash; we can re-publish.
+        for _ in range(20):
+            if mock_adapter.request_source_set_switch.call_count >= 1:
+                break
+            time.sleep(0.05)
+        assert mock_adapter.request_source_set_switch.call_count == 1
+        sink.publish()
+        for _ in range(20):
+            if mock_adapter.request_source_set_switch.call_count >= 2:
+                break
+            time.sleep(0.05)
+        assert mock_adapter.request_source_set_switch.call_count == 2
+    finally:
+        sink.stop()
+
+
+# ----------------------------------------------------------------------
+# AC-8: source_set_id from config
+
+
+def test_ac8_source_set_id_from_config() -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_ACCEPTED)])
+    a = _make_adapter(conn, _ap_config(source_set=2))
+    try:
+        a.request_source_set_switch()
+        _, _, _, _, p1 = conn.mav.command_long_calls[0]
+        assert p1 == 2.0
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-9: AZ-393 NotImplementedError placeholder replaced
+
+
+def test_ac9_no_longer_raises_not_implemented() -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_ACCEPTED)])
+    a = _make_adapter(conn, _ap_config())
+    try:
+        a.request_source_set_switch()  # would have raised NotImplementedError pre-AZ-396
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-10: STATUSTEXT severity matrix
+
+
+def test_ac10_statustext_severity_matrix(caplog: pytest.LogCaptureFixture) -> None:
+    # success → INFO
+    conn1 = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_ACCEPTED)])
+    a1 = _make_adapter(conn1, _ap_config())
+    try:
+        a1.request_source_set_switch()
+        success_severities = [sev for sev, _ in conn1.mav.statustext_calls]
+        assert int(Severity.INFO.value) in success_severities
+    finally:
+        a1.close()
+    # failure → ERROR
+    conn2 = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_FAILED)])
+    a2 = _make_adapter(conn2, _ap_config())
+    try:
+        with pytest.raises(SourceSetSwitchError):
+            a2.request_source_set_switch()
+        failure_severities = [sev for sev, _ in conn2.mav.statustext_calls]
+        assert int(Severity.ERROR.value) in failure_severities
+    finally:
+        a2.close()
+
+
+# ----------------------------------------------------------------------
+# Defence-in-depth: single-writer enforcement still applies
+
+
+def test_single_writer_thread_enforced_on_switch() -> None:
+    conn = _ConnStub(ack_queue=[_AckMsg(_CMD_SET_EKF_SOURCE_SET, _MAV_RESULT_ACCEPTED)])
+    a = _make_adapter(conn, _ap_config())
+    a.request_source_set_switch()  # bind main thread
+    err: list[BaseException] = []
+
+    def run() -> None:
+        try:
+            a.request_source_set_switch()
+        except RuntimeError as e:
+            err.append(e)
+
+    t = threading.Thread(target=run)
+    t.start()
+    t.join(timeout=2.0)
+    assert len(err) == 1
+    assert "single-writer" in str(err[0]).lower()
+    a.close()
@@ -0,0 +1,360 @@
+"""AZ-397 — QgcTelemetryAdapter AC tests."""
+
+from __future__ import annotations
+
+import logging
+import threading
+from datetime import datetime, timezone
+from types import SimpleNamespace
+from typing import Any
+from unittest import mock
+
+import numpy as np
+import pytest
+
+from gps_denied_onboard._types.fc import (
+    FcKind,
+    OperatorCommand,
+    PortConfig,
+    Severity,
+)
+from gps_denied_onboard._types.geo import LatLonAlt
+from gps_denied_onboard._types.pose import EstimatorOutput
+from gps_denied_onboard.components.c8_fc_adapter._covariance_projector import (
+    CovarianceProjector,
+)
+from gps_denied_onboard.components.c8_fc_adapter.errors import GcsAdapterConfigError
+from gps_denied_onboard.components.c8_fc_adapter.mavlink_gcs_adapter import (
+    QgcTelemetryAdapter,
+    _compute_downsample_modulo,
+)
+from gps_denied_onboard.config import load_config
+from gps_denied_onboard.config.schema import ConfigError, GcsConfig
+from gps_denied_onboard.helpers.wgs_converter import WgsConverter
+
+# ----------------------------------------------------------------------
+# Helpers
+
+
+class _MavStub:
+    def __init__(self) -> None:
+        self.global_position_int_calls: list[tuple[Any, ...]] = []
+        self.named_value_float_calls: list[tuple[Any, ...]] = []
+        self.statustext_calls: list[tuple[int, bytes]] = []
+
+    def global_position_int_send(self, *args: Any) -> None:
+        self.global_position_int_calls.append(args)
+
+    def named_value_float_send(self, time_boot_ms: int, name: bytes, value: float) -> None:
+        self.named_value_float_calls.append((time_boot_ms, name, value))
+
+    def statustext_send(self, severity: int, text: bytes) -> None:
+        self.statustext_calls.append((severity, text))
+
+
+class _ConnStub:
+    def __init__(self) -> None:
+        self.mav = _MavStub()
+        self.message_hooks: list[Any] = []
+        self.closed = False
+
+    def close(self) -> None:
+        self.closed = True
+
+
+def _config(*, summary_rate_hz: float = 2.0) -> Any:
+    env = {
+        "FC_ADAPTER": "ardupilot_plane",
+        "FC_PORT_DEVICE": "/dev/null",
+        "FC_PORT_BAUD": "921600",
+        "FC_SIGNING_KEY_SOURCE": "none",
+        "GCS_ADAPTER": "qgc_mavlink",
+        "GCS_PORT_DEVICE": "/dev/null",
+        "GCS_PORT_BAUD": "921600",
+        "GCS_SUMMARY_RATE_HZ": str(summary_rate_hz),
+    }
+    return load_config(env=env, paths=(), require_env=False)
+
+
+def _make_output(*, source_label: str = "visual_propagated", frame_id: int = 1) -> EstimatorOutput:
+    return EstimatorOutput(
+        frame_id=frame_id,
+        timestamp=datetime.now(tz=timezone.utc),
+        pose_se3=np.eye(4),
+        covariance_6x6=np.eye(6, dtype=np.float64) * 0.25,
+        source_label=source_label,
+        smoothed=False,
+        extras={"wgs84": LatLonAlt(lat_deg=50.0, lon_deg=30.0, alt_m=100.0)},
+    )
+
+
+def _make_adapter(conn: _ConnStub, cfg: Any) -> QgcTelemetryAdapter:
+    fdr = mock.MagicMock()
+    a = QgcTelemetryAdapter(
+        config=cfg,
+        wgs_converter=mock.MagicMock(),
+        covariance_projector=CovarianceProjector(fdr_client=fdr),
+        fdr_client=fdr,
+        connect_factory=lambda device, baud: conn,
+    )
+    port = PortConfig(fc_kind=FcKind.GCS_QGC, device="/dev/null", baud=921600)
+    a.open(port)
+    return a
+
+
+# ----------------------------------------------------------------------
+# AC-1: 5 -> 2 Hz downsampling
+
+
+def test_ac1_5hz_to_2hz_downsample() -> None:
+    conn = _ConnStub()
+    a = _make_adapter(conn, _config(summary_rate_hz=2.0))
+    try:
+        for i in range(100):
+            a.emit_summary(_make_output(frame_id=i))
+        # modulo = round(5/2) = 2 (round half to even gives 2; we just
+        # need parity with the documented choice). 100 / 2 = 50.
+        assert _compute_downsample_modulo(2.0) == 2
+        assert len(conn.mav.global_position_int_calls) == 50
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-2: configurable rate
+
+
+@pytest.mark.parametrize(
+    "rate_hz,expected_frames",
+    [
+        (1.0, 20),  # modulo 5 -> 100/5
+        (5.0, 100),  # modulo 1 -> no downsample
+    ],
+)
+def test_ac2_configurable_rate(rate_hz: float, expected_frames: int) -> None:
+    conn = _ConnStub()
+    a = _make_adapter(conn, _config(summary_rate_hz=rate_hz))
+    try:
+        for i in range(100):
+            a.emit_summary(_make_output(frame_id=i))
+        assert len(conn.mav.global_position_int_calls) == expected_frames
+    finally:
+        a.close()
+
+
+def test_ac2_out_of_range_rate_rejected_at_config() -> None:
+    with pytest.raises(ConfigError, match="summary_rate_hz"):
+        GcsConfig(summary_rate_hz=10.0)
+    with pytest.raises(ConfigError, match="summary_rate_hz"):
+        GcsConfig(summary_rate_hz=0.2)
+
+
+# ----------------------------------------------------------------------
+# AC-3: summary frame fields
+
+
+def test_ac3_summary_frame_fields() -> None:
+    conn = _ConnStub()
+    fdr = mock.MagicMock()
+    a = QgcTelemetryAdapter(
+        config=_config(summary_rate_hz=5.0),  # no downsample for simplicity
+        wgs_converter=mock.MagicMock(),
+        covariance_projector=CovarianceProjector(fdr_client=fdr),
+        fdr_client=fdr,
+        connect_factory=lambda device, baud: conn,
+    )
+    port = PortConfig(fc_kind=FcKind.GCS_QGC, device="/dev/null", baud=921600)
+    a.open(port)
+    try:
+        wgs = LatLonAlt(lat_deg=50.45, lon_deg=30.52, alt_m=180.0)
+        output = EstimatorOutput(
+            frame_id=1,
+            timestamp=datetime.now(tz=timezone.utc),
+            pose_se3=np.eye(4),
+            covariance_6x6=np.diag([0.25, 0.25, 9.0, 1.0, 1.0, 1.0]).astype(np.float64),
+            source_label="visual_propagated",
+            smoothed=False,
+            extras={"wgs84": wgs},
+        )
+        a.emit_summary(output)
+        assert len(conn.mav.global_position_int_calls) == 1
+        call = conn.mav.global_position_int_calls[0]
+        # global_position_int_send(time_boot_ms, lat, lon, alt_mm, rel_alt_mm, vx, vy, vz, hdg)
+        assert call[1] == int(wgs.lat_deg * 1e7)
+        assert call[2] == int(wgs.lon_deg * 1e7)
+        assert call[3] == int(wgs.alt_m * 1000.0)
+        # horiz_accuracy via NAMED_VALUE_FLOAT
+        assert len(conn.mav.named_value_float_calls) == 1
+        _, name, value = conn.mav.named_value_float_calls[0]
+        assert name == b"horiz_m"
+        expected = CovarianceProjector(fdr_client=mock.MagicMock()).to_ardupilot_horiz_accuracy_m(
+            output
+        )
+        assert value == pytest.approx(expected)
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-4: STATUSTEXT mirror
+
+
+def test_ac4_statustext_mirror() -> None:
+    conn = _ConnStub()
+    a = _make_adapter(conn, _config(summary_rate_hz=2.0))
+    try:
+        a.emit_status_text("hello", Severity.INFO)
+        assert len(conn.mav.statustext_calls) == 1
+        sev, text = conn.mav.statustext_calls[0]
+        assert sev == int(Severity.INFO.value)
+        assert text == b"hello"
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-5: operator command subscription
+
+
+def test_ac5_operator_command_subscription_invokes_callback() -> None:
+    conn = _ConnStub()
+    a = _make_adapter(conn, _config())
+    received: list[OperatorCommand] = []
+    try:
+        a.subscribe_operator_commands(received.append)
+        # Inject a PARAM_REQUEST_LIST stub
+        msg = SimpleNamespace(target_system=1, target_component=1)
+        msg.get_type = lambda: "PARAM_REQUEST_LIST"
+        msg.get_srcSystem = lambda: 42
+        # Fire every registered hook
+        for hook in conn.message_hooks:
+            hook(conn, msg)
+        assert len(received) == 1
+        cmd = received[0]
+        assert cmd.command == "PARAM_REQUEST_LIST"
+        assert cmd.payload.get("target_system") == 1
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-6: operator command FDR audit trail
+
+
+def test_ac6_operator_command_fdr_audit_trail() -> None:
+    conn = _ConnStub()
+    fdr = mock.MagicMock()
+    a = QgcTelemetryAdapter(
+        config=_config(),
+        wgs_converter=mock.MagicMock(),
+        covariance_projector=CovarianceProjector(fdr_client=fdr),
+        fdr_client=fdr,
+        connect_factory=lambda device, baud: conn,
+    )
+    port = PortConfig(fc_kind=FcKind.GCS_QGC, device="/dev/null", baud=921600)
+    a.open(port)
+    try:
+        a.subscribe_operator_commands(lambda _cmd: None)
+        msg = SimpleNamespace(target_system=1, target_component=1, command=400)
+        msg.get_type = lambda: "COMMAND_LONG"
+        msg.get_srcSystem = lambda: 7
+        for hook in conn.message_hooks:
+            hook(conn, msg)
+        operator_records = [
+            call
+            for call in fdr.enqueue.mock_calls
+            if call.args[0].payload.get("kind") == "c8.gcs.operator_command"
+        ]
+        assert len(operator_records) == 1
+        rec = operator_records[0].args[0].payload
+        assert rec["kv"]["command"] == "COMMAND_LONG"
+        assert rec["kv"]["source_system"] == 7
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-7: single-writer thread for outbound
+
+
+def test_ac7_single_writer_thread() -> None:
+    conn = _ConnStub()
+    a = _make_adapter(conn, _config(summary_rate_hz=5.0))
+    err: list[BaseException] = []
+    try:
+        a.emit_summary(_make_output())
+
+        def run() -> None:
+            try:
+                a.emit_summary(_make_output(frame_id=2))
+            except RuntimeError as e:
+                err.append(e)
+
+        t = threading.Thread(target=run)
+        t.start()
+        t.join(timeout=2.0)
+        assert len(err) == 1
+        assert "single-writer" in str(err[0]).lower()
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-8: first emit logged once
+
+
+def test_ac8_first_emit_logged_once(caplog: pytest.LogCaptureFixture) -> None:
+    conn = _ConnStub()
+    a = _make_adapter(conn, _config(summary_rate_hz=5.0))
+    try:
+        with caplog.at_level(logging.INFO):
+            for i in range(5):
+                a.emit_summary(_make_output(frame_id=i))
+        first = [
+            r for r in caplog.records if getattr(r, "kind", None) == "c8.gcs.first_summary_emit"
+        ]
+        assert len(first) == 1
+    finally:
+        a.close()
+
+
+# ----------------------------------------------------------------------
+# AC-9: WGS84 round-trip (defensive)
+
+
+def test_ac9_wgs84_round_trip_within_1cm() -> None:
+    # Round-trip a known lat/lon through WgsConverter ECEF and back.
+    origin = LatLonAlt(lat_deg=50.45, lon_deg=30.52, alt_m=180.0)
+    enu = WgsConverter.latlonalt_to_local_enu(
+        origin, LatLonAlt(lat_deg=50.4501, lon_deg=30.5201, alt_m=180.5)
+    )
+    recovered = WgsConverter.local_enu_to_latlonalt(origin, enu)
+    expected = LatLonAlt(lat_deg=50.4501, lon_deg=30.5201, alt_m=180.5)
+    # 1 cm threshold — pyproj's ENU round-trip is sub-millimetre at
+    # these distances; we keep the AC's 1 cm threshold as the contract.
+    enu_residual = WgsConverter.latlonalt_to_local_enu(expected, recovered)
+    assert np.linalg.norm(enu_residual) < 0.01
+
+
+# ----------------------------------------------------------------------
+# AC-10: GcsAdapterConfigError on bad config (config-load path)
+
+
+def test_ac10_gcs_config_error_on_bad_rate() -> None:
+    with pytest.raises(ConfigError, match="summary_rate_hz"):
+        GcsConfig(summary_rate_hz=6.0)
+
+
+def test_ac10_open_rejects_wrong_fc_kind() -> None:
+    conn = _ConnStub()
+    fdr = mock.MagicMock()
+    a = QgcTelemetryAdapter(
+        config=_config(),
+        wgs_converter=mock.MagicMock(),
+        covariance_projector=CovarianceProjector(fdr_client=fdr),
+        fdr_client=fdr,
+        connect_factory=lambda device, baud: conn,
+    )
+    port = PortConfig(fc_kind=FcKind.ARDUPILOT_PLANE, device="/dev/null", baud=921600)
+    with pytest.raises(GcsAdapterConfigError, match="GCS_QGC"):
+        a.open(port)