[AZ-698] Tlog trim + mid-flight alignment for replay

Adds find_aligned_window cross-correlation (NCC, per-window unit norm)
between IMU energy and video optical-flow magnitude. Returns
AlignedWindow{tlog_start_ns, tlog_end_ns, offset_ms, confidence,
used_fallback}, with fallback to head-takeoff on low confidence to
preserve AZ-405 behavior. TlogReplayFcAdapter honors tlog_start_ns and
skips pre-window messages. New --auto-trim CLI flag, mutex with
--time-offset-ms. AC-1..AC-4 covered by unit tests; AC-5 skipped (no
real flight_derkachi.mp4 in repo). 106 tests pass in regression slice.
Zero new mypy --strict errors.

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

_docs/02_tasks/todo/AZ-698_tlog_trim_midflight_alignment.md

@@ -1,118 +0,0 @@
-# Tlog trim + mid-flight alignment for replay
-
-**Task**: AZ-698_tlog_trim_midflight_alignment
-**Name**: Trim tlog to video window + align mid-flight slices via cross-correlation
-**Description**: Extend `replay_input/auto_sync.py` and `TlogReplayFcAdapter` to handle the case where the video is a mid-flight slice of a longer tlog (not the takeoff). Adds `find_aligned_window` (cross-correlation of IMU energy vs video optical-flow magnitude) and a `--auto-trim` CLI flag.
-**Complexity**: 5 points
-**Dependencies**: AZ-697
-**Component**: replay_input + c8_fc_adapter
-**Tracker**: AZ-698
-**Epic**: AZ-696
-
-## Problem
-
-`replay_input/auto_sync.py::detect_tlog_takeoff` walks the tlog HEAD for
-the takeoff event (sustained vertical accel + attitude rate). When the
-uploaded video covers a **mid-flight slice** (e.g., 20–25 min into a
-30 min flight), takeoff detection lands at t=0 and the resulting offset
-is garbage. The replay coordinator then streams the entire tlog
-start-to-end, wasting I/O on the leading minutes and computing
-estimates against stale tlog samples.
-
-The user's pipeline framing: "tlog is usually bigger than video, and
-usually the last chunk in tlog is relevant" — the system must locate
-the video's window within the tlog and trim accordingly.
-
-## Outcome
-
-- A new `find_aligned_window(tlog_path, video_path, config) -> AlignedWindow`
-  returns `(tlog_start_ns, tlog_end_ns, offset_ms, confidence)`.
-- `TlogReplayFcAdapter.open()` honors `tlog_start_ns` — seeks past
-  pre-window messages so downstream only sees the relevant slice.
-- `gps-denied-replay --auto-trim` is the default for uploads that don't
-  pass `--time-offset-ms` or `--skip-auto-sync`.
-- Existing takeoff-aligned Derkachi clip continues to pass AC-9 (no
-  regression on AZ-405).
-
-## Scope
-
-### Included
-- New `find_aligned_window` algorithm — cross-correlation of:
-  - IMU energy stream (10 Hz subsampled `|a| − 1g` from `RAW_IMU`/`SCALED_IMU2`)
-  - Video optical-flow magnitude (existing `_compute_flow_magnitudes`)
-- New `AlignedWindow` DTO under `replay_input/interface.py`.
-- `TlogReplayFcAdapter._timestamp_filter(tlog_start_ns)` seek logic.
-- `gps-denied-replay --auto-trim` CLI flag wiring.
-- Tests: takeoff-aligned regression + synthetic mid-flight scenario.
-
-### Excluded
-- Real-flight validation runner — AZ-699 (T3).
-- Map visualization — AZ-700 (T4).
-- HTTP API — AZ-701 (T5).
-- Camera calibration — AZ-702 (T6).
-
-## Acceptance Criteria
-
-**AC-1: Backward-compat on takeoff-aligned clip**
-Given the existing Derkachi 60 s clip with synthesized tlog
-When `find_aligned_window` runs
-Then it returns `offset_ms` within ± 50 ms of the current `auto_sync.compute_offset` result
-
-**AC-2: Mid-flight alignment**
-Given a synthetic scenario: tlog covering 0–300 s, video covering 100–110 s with motion onset at tlog t=105 s
-When `find_aligned_window` runs
-Then `tlog_start_ns ≈ 100 s`, `tlog_end_ns ≈ 110 s`, `offset_ms` places video t=0 at tlog t=100 s
-
-**AC-3: Tlog trim honored by replay adapter**
-Given `TlogReplayFcAdapter` opened with `tlog_start_ns = 100 s`
-When messages flow
-Then only messages with `_timestamp ≥ 100 s` reach subscribers
-
-**AC-4: AC-9 frame-window validator passes for both scenarios**
-Given the resolved offset from AC-1 or AC-2
-When the AC-9 validator runs on the aligned window
-Then it returns 0 (≥ 95 % match)
-
-**AC-5: End-to-end CLI smoke**
-Given `gps-denied-replay --auto-trim --video derkachi.mp4 --tlog derkachi.tlog`
-When the run completes
-Then exit code is 0 and the output JSONL is non-empty
-
-## Non-Functional Requirements
-
-**Performance**
-- Alignment over a 30-min tlog completes in < 30 s on Tier-1 hardware (10 Hz subsampled IMU stream).
-
-**Reliability**
-- Low confidence (< `low_confidence_threshold`) falls back to head-takeoff detection (existing behavior).
-
-## Unit Tests
-
-| AC Ref | What to Test | Required Outcome |
-|--------|-------------|-----------------|
-| AC-1 | Takeoff-aligned offset match | Within ± 50 ms of compute_offset |
-| AC-2 | Mid-flight window discovery | Correct (start_ns, end_ns) |
-| AC-3 | Adapter seek skips pre-window | First emitted ts ≥ tlog_start_ns |
-| AC-4 | Validator on aligned scenarios | Returns 0 |
-
-## Blackbox Tests
-
-| AC Ref | Initial Data/Conditions | What to Test | Expected Behavior | NFR References |
-|--------|------------------------|-------------|-------------------|----------------|
-| AC-5 | Real derkachi inputs + --auto-trim | Full replay CLI run | Clean exit 0 + non-empty JSONL | — |
-
-## Constraints
-
-- Reuse the existing `_find_sustained_event` window-scan utility — no new generic algorithms.
-- IMU subsampling MUST be deterministic (AC-10 across the rest of the replay path).
-- `tlog_start_ns` seek MUST not break the existing AZ-611 `--skip-auto-sync` path.
-
-## Risks & Mitigation
-
-**Risk 1: False maxima during steady cruise**
-- *Risk*: Cross-correlation of steady-state cruise IMU + uniform video flow can have multiple equal-height peaks.
-- *Mitigation*: Report `combined_confidence`; below threshold falls back to head-takeoff or explicit offset.
-
-**Risk 2: Performance on long tlogs**
-- *Risk*: Multi-hour tlogs would slow naive correlation.
-- *Mitigation*: Subsample both streams to 10 Hz before FFT-based correlation.