feat: event-based walker detector tuned to real 7' overhead mount

Replace per-track line-crossing counter with a single event state machine
gated by foreground pixel count (ENTER=250, EXIT=150) and finalized by
quiet-exit or timeout. Direction inferred from centroid excursion
(up_score vs down_score) on quiet-exit fires, and from net displacement
(last_c vs first_c) on timeout fires.

Tuning reflects bench data at the intended 7' overhead mount: walkers
produce smaller centroid excursions than originally modelled, so
EXTENT gates, MIN_TRAJ, MAX_FRAMES and REFRACTORY were all relaxed from
their initial guesses. Constants and rationale live in firmware/lib/cv/cv.h.

Bench results (8 isolated walks, 4 entries + 4 exits):
  * Event detection: 8/8 (100%)
  * Aggregate entries+exits split: 4+4 (matches)
  * Per-walk direction labelling: 4/8 (~50%)

Document explicitly that per-walk direction is unreliable at this mount
and that downstream analytics should trust only gross traffic
(entries + exits). Recovering direction would require a physical mount
change or a richer signal; both are out of scope for v1.

Tooling:
  * tools/replay_logs.py — replay event state machine against captured
    [F] diagnostic lines, for offline tuning without flash-test loops.
  * firmware/src/main_capture.cpp + tools/capture_frames.py +
    tools/replay_frames.py — raw-frame capture firmware and Python port
    of the detector, kept in tree for future iteration even though the
    TimerCamera-F serial driver stripped specific byte ranges in testing
    and log-based replay became the working path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1 +1,6 @@
 .worktrees/
+.agent/
+.claude/
+graphify-out/
+firmware/.pio/
+*.log

README.md

@@ -1,6 +1,8 @@
 # DoorCounter
 
-Retail door traffic counter using M5Stack TimerCamera-F (ESP32 + OV3660). Counts entries/exits via overhead camera CV, passively scans BLE foot traffic, and reports hourly to `logs.research.bike`.
+Retail door traffic counter using M5Stack TimerCamera-F (ESP32 + OV3660). Counts walker traversals via overhead camera CV, passively scans BLE foot traffic, and reports hourly to `logs.research.bike`.
+
+> **Known limitation — directional accuracy.** This firmware reports counts as `{entries, exits}` for API compatibility, but **per-walk direction labelling is not reliable at the current mount (7' overhead, straight down).** In bench testing, event detection was 100% (8/8 walks detected) while per-walk direction matched the physical walk only ~50% of the time — the centroid trajectories produced by entries and exits were nearly indistinguishable. **The number to trust is gross traffic: `entries + exits` ≈ total walkers through the doorway.** The directional split is an unreliable best-effort heuristic. See [Directional counting](#directional-counting) for why.
 
 ## Hardware
 
@@ -21,7 +23,8 @@ pio run -t upload --upload-port /dev/ttyUSB0
 
 | Module | Behavior |
 |--------|----------|
-| CV pipeline | 5 fps, 96×96 grayscale, blob tracking, line-crossing count |
+| CV pipeline | 5 fps, 96×96 grayscale, event-based walker detector (foreground-count state machine; centroid-trajectory direction heuristic) with post-fire refractory period |
+| Detection LED | Single blink on entry, double blink on exit (preserves upload/no-WiFi status LED) |
 | BLE scanner | Continuous passive scan; deinits during hourly upload to free heap |
 | Reporter | Hourly HMAC-signed POST; 60s boot report for fast connectivity check |
 | Provisioning | Captive portal AP on first boot for WiFi setup |
@@ -32,6 +35,71 @@ pio run -t upload --upload-port /dev/ttyUSB0
 - **First report**: 60 seconds after NTP sync (connectivity check)
 - **Subsequent reports**: every 3600 seconds
 
+### Counting model — event-based walker detector
+
+The CV pipeline is a **single event state machine** (no per-blob tracking
+for counting). Per-frame foreground pixel count gates event start and end;
+centroid trajectory within the active event decides direction.
+
+**Event lifecycle:**
+1. **Idle → Active**: `fg_count ≥ CV_EVENT_ENTER_THRESH` (250 px) fires event start.
+   Background updates freeze while the event is active so the walker does
+   not get absorbed into the baseline.
+2. **Active accumulation**: every frame updates `first_c` (once), `min_c`,
+   `max_c`, `last_c`, `min_y_seen`, `max_y_seen`, and the frame count.
+3. **Active → End** (either):
+   - **Quiet exit**: `fg_count < CV_EVENT_EXIT_THRESH` (150 px) for
+     `CV_EVENT_QUIET_FRAMES` (3) consecutive frames — walker has left.
+   - **Timeout**: `event_frame_count > CV_EVENT_MAX_FRAMES` (25 frames ≈ 5s).
+4. On end, the event is finalized: gated by minimum duration, vertical
+   extent (must span a large fraction of the frame), and minimum centroid
+   trajectory magnitude. Background snaps to the current frame.
+5. A **refractory period** (`CV_EVENT_REFRACTORY_FRAMES` = 10 ≈ 2s) after
+   a fire blocks a new event from starting — absorbs residual lingering
+   motion that would otherwise double-count.
+
+**Direction heuristic** (applied only if the event passes all gates):
+- `up_score   = first_c − min_c` (how far centroid excursed upward)
+- `down_score = max_c   − first_c` (how far it excursed downward)
+- Quiet-exit events: `is_entry = (up_score ≥ down_score)`
+- Timeout events: `is_entry = (last_c < first_c)` — net displacement is
+  more reliable than excursion when the walker is still in frame at timeout.
+
+Per-mount convention: centroid moving **up through the frame** (y decreasing)
+= **entry** into the store.
+
+### Directional counting — known limitation
+
+**Per-walk direction labelling is unreliable at the current mount.** In
+bench testing (8 alternating entry/exit walks at 4s intervals, 7' overhead
+mount pointing straight down):
+
+- **Event detection**: 8/8 (100%) — every walk produced exactly one event.
+- **Aggregate split**: 4 entries + 4 exits — matches the 4+4 ground truth.
+- **Per-walk direction**: 4/8 (50%) — essentially a coin flip.
+
+At this mount, entries and exits produce nearly identical centroid
+trajectories: both begin near mid-frame (walker is already large when
+`fg_count` crosses 250), both reach a peak excursion toward the top, and
+both end near mid-frame (walker's tail is still visible when `fg_count`
+drops below 150). No heuristic over the recorded centroid statistics
+separates them with better than ~50% accuracy on alternating walks.
+
+**What we ship, and what the server should trust:**
+- **Gross traffic (`entries + exits`) is accurate.** This is the number
+  downstream analytics should use as "people through the door this hour."
+- **Directional split is reported but unreliable.** Treat individual
+  `entries` and `exits` values as a best-effort labelling. Do not infer
+  net flow or dwell from them.
+
+To actually recover per-walk direction would require either a physical
+change (raise or tilt the camera so walkers enter/leave through the frame
+edges) or a richer signal than centroid statistics (e.g. time-resolved
+optical flow, or a second sensor). That work is out of scope for v1.
+
+See `firmware/lib/cv/cv.h` for tuning constants and `cv.cpp` for the
+finalize logic.
+
 ## Operator Setup
 
 ### 1. Flash firmware
@@ -55,6 +123,12 @@ python tools/flash_device.py \
 
 WiFi credentials are optional — if omitted, device starts captive portal on boot.
 
+> **Re-provision after firmware uploads.** Flashing firmware via
+> `pio run -t upload` may clear the NVS partition on this board. If the device
+> boots into a ~1 Hz LED blink (the "not provisioned" fatal state) after a
+> firmware update, re-run `flash_device.py` with the same credentials. See
+> [Troubleshooting](#troubleshooting).
+
 ### 3. OTA updates
 
 ```bash
@@ -70,7 +144,7 @@ python tools/ota_push.py \
 3. Connect phone to `DoorCounter-Setup` WiFi
 4. Browser opens automatically → enter store WiFi password → done
 
-**LED indicators**: Red = no WiFi · Blue = counting · Yellow = uploading
+**LED indicators**: Red = no WiFi · Blue = counting · Yellow = uploading · Brief flash (×1) on entry · Brief flash (×2) on exit
 
 ## API
 
@@ -90,7 +164,9 @@ All requests are HMAC-SHA256 signed. See [design spec](docs/superpowers/specs/20
 DoorCounter/
 ├── firmware/
 │   ├── platformio.ini
-│   ├── lib/hmac/          — HMAC-SHA256 signing library
+│   ├── lib/
+│   │   ├── cv/            — CV pipeline (event state machine, centroid-trajectory direction)
+│   │   └── hmac/          — HMAC-SHA256 signing library
 │   └── src/
 │       ├── main.cpp       — FreeRTOS tasks, boot sequence
 │       ├── config.*       — NVS read/write
@@ -100,8 +176,24 @@ DoorCounter/
 │       └── reporter.*     — hourly batch POST + local buffer
 ├── tools/
 │   ├── flash_device.py    — NVS provisioning script
-│   └── ota_push.py        — OTA push script
-├── docs/superpowers/specs/
-│   └── 2026-04-13-door-counter-design.md
+│   ├── ota_push.py        — OTA push script
+│   └── serial_monitor.py  — reset + read serial with timestamps (diagnostic)
+├── docs/
+│   ├── server-prompt-crossing-cooldown.md — server-side coordination notes
+│   └── superpowers/specs/2026-04-13-door-counter-design.md
 └── server/                — API server (separate deployment)
 ```
+
+## Troubleshooting
+
+| Symptom | Likely cause | Remedy |
+|---------|--------------|--------|
+| ~1 Hz LED blink after boot, no serial beyond `esp_core_dump_flash: No core dump partition found!` | NVS missing `device_id` / `location_id` / `hmac_secret`. Commonly triggered by a firmware upload wiping NVS. | Re-run `flash_device.py` with the device's known credentials. |
+| Device stays on `DoorCounter-Setup` AP instead of joining customer WiFi | SSID/password in NVS wrong, or network out of range. | Connect phone to `DoorCounter-Setup` → captive portal → re-enter WiFi. Or reflash NVS with correct `--wifi-ssid` / `--wifi-password`. |
+| No entries/exits counted for a known-walking doorway | WiFi captive portal still up (camera task starts only after connect); or camera blocked/unfocused. | Check LED: solid on = booting/uploading, off = counting. Run `serial_monitor.py` to see `[CV] entry/exit` log lines. |
+
+Capture a boot log with timestamps:
+
+```bash
+python tools/serial_monitor.py --port /dev/ttyUSB0 --reset --timestamp --seconds 30
+```

docs/server-prompt-crossing-cooldown.md

@@ -0,0 +1,78 @@
+# Server-Side Prompt — Crossing Cooldown Awareness
+
+> Give this to your server-side agent after the firmware commit that introduces
+> `CV_CROSSING_COOLDOWN_FRAMES` in `firmware/lib/cv/cv.h` has been flashed to devices.
+
+## Context
+
+The DoorCounter firmware now enforces a **per-direction crossing cooldown** in
+its CV pipeline. After a counted entry, subsequent entries within 5 frames
+(~1 second at 5 fps) are silently dropped on-device. Exits follow the same
+rule independently. This is a device-side fix for the known track-churn bug
+(single person producing 5+ counts per visit when their blob briefly drops
+below the minimum-blob-pixel threshold).
+
+Constants live in `firmware/lib/cv/cv.h`:
+
+```c++
+static const uint32_t CV_CROSSING_COOLDOWN_FRAMES = 5; // per-direction
+```
+
+Cooldown is **fixed at compile time**. It is **not** currently a server-
+pushable tuning parameter.
+
+## What the server should do
+
+1. **Expect lower per-hour entry/exit counts** from devices running this
+   firmware compared to their historical baseline. This reflects suppression
+   of false positives, not a device regression. Do not alert on the drop.
+
+2. **If you have a per-device tuning-config push mechanism** (the one planned
+   in `.agent/plan.md` — server-push CV config via heartbeat response), add
+   `cooldown_frames` to the sendable tuning set with:
+   - Default: `5`
+   - Valid range: `0..60` (0 disables cooldown; 60 ≈ 12s at 5 fps)
+   - Semantics: per-direction, applied to both entries and exits
+   - Persist alongside other CV tuning keys in NVS under a new key `cv_cool`.
+   - Bump the `cfg_version` scheme accordingly.
+
+   **Do not ship this server-side change yet** — the firmware change in this
+   commit keeps the cooldown as a compile-time constant. A future firmware
+   commit on `feature/server-push-config` will expose it as a runtime
+   tunable and bump `cfg_version`. Coordinate the rollout: firmware first,
+   then server.
+
+3. **Dashboard**: if you render device CV parameters in a per-device settings
+   view, add a read-only row "Crossing cooldown (frames): 5" sourced from
+   the firmware's compiled default. Mark it editable only once the firmware
+   exposes it as a tunable.
+
+4. **Telemetry (optional, low priority)**: consider adding a field
+   `suppressed_crossings_delta` to the heartbeat or camera-events payload
+   so operators can see how often cooldown is kicking in. This would require
+   a firmware change; flag it as future work only if churn continues.
+
+## What NOT to do
+
+- Do not attempt to push `cooldown_frames` via the existing config channel
+  today — the firmware will ignore unknown fields, which is fine, but
+  shipping server changes that assume the firmware-side plumbing exists
+  will break the integration contract.
+- Do not "correct" the lower counts via server-side multiplication. The
+  cooldown is the correct behavior; old counts were inflated by the churn
+  bug.
+
+## Verification checklist
+
+- [ ] Historical counts chart annotated with "firmware v{N} deployed"
+      marker on the rollout date.
+- [ ] Per-device tuning view renders cooldown row (read-only for now).
+- [ ] No alert fires on the per-device count drop post-rollout.
+
+## Reference
+
+- Firmware change: `firmware/lib/cv/cv.h` (`CV_CROSSING_COOLDOWN_FRAMES`),
+  `firmware/lib/cv/cv.cpp` (suppression logic in `cv_process`).
+- Design spec: `docs/superpowers/specs/2026-04-13-door-counter-design.md`
+  § 3.1 "Counting logic".
+- Unit test: `firmware/test/test_cv/test_cv.cpp::test_cooldown_suppresses_rapid_re_entry`.

docs/superpowers/specs/2026-04-13-door-counter-design.md

@@ -13,7 +13,7 @@
 [TimerCamera-F Device]
   ├── Provisioning module   — captive portal AP on first boot
   ├── Config store          — NVS: device_id, location_id, HMAC secret, WiFi creds, line_offset
-  ├── Camera + CV module    — captures frames, runs line-crossing counter
+  ├── Camera + CV module    — captures frames, runs event-based walker detector
   ├── BLE scanner           — continuous passive scan (WiFi coexistence mode)
   ├── Report buffer         — accumulates counts in RAM, flushes hourly
   └── HTTP client           — HMAC-signed POSTs to logs.research.bike
@@ -89,15 +89,38 @@ Capture → Grayscale → Downscale 96×96 → Frame diff → Threshold → Blob
 | Downscale | Bilinear to 96×96 (~11× compute reduction) |
 | Frame diff | Absolute difference against rolling background (updated every ~2s when no motion) |
 | Threshold | Pixels > 30 intensity delta = foreground |
-| Blob detect | Connected components; blobs < 8×8 px discarded as noise |
-| Centroid track | Nearest-centroid matching frame-to-frame (max 15px), tracks persist up to 10 missed frames |
-| Line crossing | Virtual horizontal line at configurable vertical position (default: 50% of frame height) |
+| Event state machine | Single global state machine (not per-blob). Per-frame `fg_count` (total foreground pixels) gates event start and end. |
+| Event start | `fg_count ≥ CV_EVENT_ENTER_THRESH` (250 px) → event becomes active. Background updates freeze for the event's duration so the walker does not blend into the baseline. |
+| Event accumulation | Each frame records `first_c` (centroid_y at start), running `min_c` / `max_c` / `last_c`, vertical extents (`min_y_seen`, `max_y_seen`), and frame count. |
+| Event end | Either **quiet exit** (`fg_count < CV_EVENT_EXIT_THRESH` (150 px) for `CV_EVENT_QUIET_FRAMES` (3) consecutive frames) or **timeout** (`event_frame_count > CV_EVENT_MAX_FRAMES` (25)). On end, background snaps to the current frame. |
+| Fire gates | Duration ≥ `CV_EVENT_MIN_FRAMES` (5), `min_y_seen ≤ CV_EVENT_EXTENT_TOP` (25) AND `max_y_seen ≥ CV_EVENT_EXTENT_BOT` (50) — event must span a large fraction of the frame — AND `max(up_score, down_score) ≥ CV_EVENT_MIN_TRAJ` (5) |
+| Refractory | `CV_EVENT_REFRACTORY_FRAMES` (10 ≈ 2s) after a fire, the machine refuses to start a new event — absorbs lingering motion of the just-counted walker. |
 
-**Counting logic:**
-- Centroid crosses line top→bottom = **entry**
-- Centroid crosses line bottom→top = **exit**
+**Direction heuristic (applied after fire gates pass):**
+- `up_score   = first_c − min_c` (peak upward centroid excursion)
+- `down_score = max_c   − first_c` (peak downward centroid excursion)
+- **Quiet-exit fires**: `is_entry = (up_score ≥ down_score)`
+- **Timeout fires**: `is_entry = (last_c < first_c)` — walker is still in frame at timeout, so net displacement is a better signal than excursion.
 
-Counts accumulate as `{entries, exits}` in RAM and reset each hour on report.
+Per-mount convention: centroid moving **up through the frame** (y decreasing) = **entry** into the store.
+
+**Counting surface**: `{entries, exits}` accumulate in RAM and reset each hour on report.
+
+**Directional accuracy is best-effort, not guaranteed.** In bench testing at the intended 7' overhead straight-down mount:
+
+| Metric | Result |
+|--------|--------|
+| Event detection | 8/8 walks (100%) |
+| Aggregate entry/exit split | 4+4 vs ground-truth 4+4 (matches) |
+| Per-walk direction labelling | 4/8 (50%) — no better than chance |
+
+At this mount, entries and exits produce nearly identical centroid trajectories: the walker is already large when `fg_count` crosses 250 (so `first_c` is always near mid-frame), their tail is still visible when `fg_count` drops below 150 (so `last_c` is always near mid-frame), and the excursion in between peaks upward for both directions. No statistic computable from (`first_c`, `min_c`, `max_c`, `last_c`, duration) separates them reliably.
+
+**Contract with downstream consumers (API and analytics):**
+- **`entries + exits` is the trustworthy number** — it is the count of walkers through the doorway in the hour. Use this as "foot traffic."
+- **Individual `entries` and `exits` are reported for API shape compatibility, but should not be relied on for net flow, dwell, or any per-direction analysis.**
+
+Recovering true direction requires either a physical change (tilt or raise the camera so walkers pass fully through the frame edges) or a richer signal (time-resolved centroid trajectory, optical flow, secondary sensor). Both are out of scope for v1.
 
 ---
 

firmware/lib/cv/cv.cpp

@@ -5,8 +5,21 @@
 #include <algorithm>
 #include <vector>
 
+static void event_reset(CVState& s) {
+    s.event_active       = false;
+    s.event_start_frame  = 0;
+    s.event_frame_count  = 0;
+    s.event_peak_n       = 0;
+    s.event_first_c      = -1.0f;
+    s.event_last_c       = -1.0f;
+    s.event_min_c        = (float)CV_H;
+    s.event_max_c        = -1.0f;
+    s.event_min_y_seen   = CV_H;
+    s.event_max_y_seen   = -1;
+    s.event_quiet_count  = 0;
+}
+
 void cv_init(CVState& state) {
-    // Initialize members directly — avoid CVState{} temporary which puts 9KB on stack
     memset(state.background, 0, sizeof(state.background));
     state.bg_valid          = false;
     state.last_motion_frame = 0;
@@ -15,6 +28,8 @@ void cv_init(CVState& state) {
     state.tracks.clear();
     state.entries = 0;
     state.exits   = 0;
+    state.last_fire_frame = 0;
+    event_reset(state);
 }
 
 void cv_reset_counts(CVState& state) {
@@ -24,9 +39,6 @@ void cv_reset_counts(CVState& state) {
 
 struct Point { int x, y; };
 
-// Note: queue may grow to CV_PIXELS entries (~72KB) on large blobs.
-// Requires PSRAM (enabled via -DBOARD_HAS_PSRAM in platformio.ini).
-// BFS flood fill. Marks visited pixels (sets fg to 0). Returns {-1,-1} if blob < CV_MIN_BLOB_PX.
 static std::pair<float,float> extract_blob(uint8_t* fg, int start_x, int start_y) {
     std::vector<Point> queue;
     queue.reserve(512);
@@ -58,7 +70,7 @@ static std::pair<float,float> extract_blob(uint8_t* fg, int start_x, int start_y
 
 static std::vector<std::pair<float,float>> find_centroids(const uint8_t* fg) {
     std::vector<std::pair<float,float>> result;
-    static uint8_t fg_copy[CV_PIXELS];  // static to avoid 9KB stack allocation
+    static uint8_t fg_copy[CV_PIXELS];
     memcpy(fg_copy, fg, CV_PIXELS);
 
     for (int y = 0; y < CV_H; y++) {
@@ -80,8 +92,62 @@ static void frame_diff(const uint8_t* frame, const uint8_t* bg,
     }
 }
 
-CVResult cv_process(CVState& state, const uint8_t* frame, uint8_t line_pct) {
-    CVResult result = {0, 0};
+// Decide whether the just-ended event should fire and in which direction.
+// Up-through-frame (centroid excursion from high y toward low y) maps to
+// ENTRY per mount convention.
+static void finalize_event(CVState& s, CVResult& result) {
+    if (s.event_frame_count < CV_EVENT_MIN_FRAMES) return;
+    // Note: no MAX_FRAMES rejection here. An event that runs the full duration
+    // may still be a valid walker whose fg_count stayed above EXIT_THRESH due
+    // to a stale bg or an AEC-driven lighting shift. Extent + MIN_TRAJ gates
+    // below already reject stationary-person / wobble events.
+    if (s.event_min_y_seen > CV_EVENT_EXTENT_TOP)  return;
+    if (s.event_max_y_seen < CV_EVENT_EXTENT_BOT)  return;
+
+    // Direction from centroid excursion relative to event start.
+    // up_score: how far centroid excursed upward (smaller y) from first_c.
+    // down_score: how far it excursed downward (larger y) from first_c.
+    float up_score   = s.event_first_c - s.event_min_c;
+    float down_score = s.event_max_c   - s.event_first_c;
+
+    float winning = (up_score >= down_score) ? up_score : down_score;
+    if (winning < CV_EVENT_MIN_TRAJ) return;
+
+    // Timeout-aware direction. Quiet-exit events (fg fell below EXIT_THRESH)
+    // have walker fully out of frame → min/max excursion bracket the true
+    // traversal and up/down scores are reliable. Timeout events (event hit
+    // MAX_FRAMES while still elevated) captured both an approach and a
+    // departure within the window, so excursion measures the walker's
+    // *range in frame* rather than direction — an entry walker who paused
+    // near the top, then drifted back toward the middle before timeout
+    // gets (wrongly) called an entry by up-score even though net motion is
+    // mixed. For those, the net first→last centroid displacement is a
+    // better direction signal (it's where the walker ended up, not just
+    // where they peaked).
+    bool timed_out = (s.event_frame_count > CV_EVENT_MAX_FRAMES);
+    bool is_entry;
+    if (timed_out) {
+        is_entry = (s.event_last_c < s.event_first_c);
+    } else {
+        is_entry = (up_score >= down_score);
+    }
+    if (is_entry) {
+        s.entries++;
+        result.entries_delta++;
+    } else {
+        s.exits++;
+        result.exits_delta++;
+    }
+    s.last_fire_frame = s.frame_index;
+    result.fire_first_c  = s.event_first_c;
+    result.fire_min_c    = s.event_min_c;
+    result.fire_max_c    = s.event_max_c;
+    result.fire_last_c   = s.event_last_c;
+    result.fire_duration = s.event_frame_count;
+}
+
+CVResult cv_process(CVState& state, const uint8_t* frame, uint8_t /*line_pct*/) {
+    CVResult result = {0, 0, 0, -1, -1, -1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0};
     state.frame_index++;
 
     if (!state.bg_valid) {
@@ -90,85 +156,147 @@ CVResult cv_process(CVState& state, const uint8_t* frame, uint8_t line_pct) {
         return result;
     }
 
-    static uint8_t fg[CV_PIXELS];  // static: avoids 9KB on task stack
+    static uint8_t fg[CV_PIXELS];
     frame_diff(frame, state.background, fg, CV_PIXELS);
 
-    int fg_count = 0;
-    for (int i = 0; i < CV_PIXELS; i++) fg_count += fg[i];
-
-    bool motion = fg_count > CV_MIN_BLOB_PX;
-    if (!motion) {
-        if (state.frame_index - state.last_motion_frame > 10) {
-            memcpy(state.background, frame, CV_PIXELS);
+    // Running-average background blend: bg = (31*bg + frame)/32. Adapts to
+    // slow scene drift during idle periods. Frozen during an active event so
+    // the walker's signature is never absorbed — otherwise bg retains a
+    // "ghost" of the walker for ~30 frames after they leave, keeping fg_count
+    // elevated and preventing subsequent walkers from producing a clean
+    // trajectory.
+    if (!state.event_active) {
+        for (int i = 0; i < CV_PIXELS; i++) {
+            state.background[i] = (uint8_t)(((uint16_t)state.background[i] * 31 + frame[i]) >> 5);
         }
+    }
+
+    int fg_count = 0;
+    int min_y = CV_H, max_y = -1;
+    long sum_y = 0;
+    for (int y = 0; y < CV_H; y++) {
+        const uint8_t* row = &fg[y * CV_W];
+        int row_count = 0;
+        for (int x = 0; x < CV_W; x++) row_count += row[x];
+        if (row_count > 0) {
+            if (y < min_y) min_y = y;
+            if (y > max_y) max_y = y;
+            sum_y += (long)row_count * y;
+            fg_count += row_count;
+        }
+    }
+    result.fg_count      = fg_count;
+    result.fg_min_y      = (fg_count > 0) ? min_y : -1;
+    result.fg_max_y      = (fg_count > 0) ? max_y : -1;
+    result.fg_centroid_y = (fg_count > 0) ? ((float)sum_y / fg_count) : -1.0f;
+
+    // Hard self-heal: if more than half the frame is fg, bg is catastrophically
+    // wrong. Snap and skip the event machine this frame.
+    if (fg_count > CV_PIXELS / 2) {
+        memcpy(state.background, frame, CV_PIXELS);
+        state.last_motion_frame = state.frame_index;
+        if (state.event_active) event_reset(state);
+        return result;
+    }
+
+    // Diagnostic track management (no effect on counting).
+    bool motion = fg_count > CV_MIN_BLOB_PX;
+    if (motion) {
+        state.last_motion_frame = state.frame_index;
+        auto centroids = find_centroids(fg);
+        std::vector<bool> centroid_matched(centroids.size(), false);
+        for (auto& track : state.tracks) {
+            float best_dist = CV_MAX_MOVE * CV_MAX_MOVE;
+            int   best_idx  = -1;
+            for (int i = 0; i < (int)centroids.size(); i++) {
+                if (centroid_matched[i]) continue;
+                float dx = centroids[i].first  - track.x;
+                float dy = centroids[i].second - track.y;
+                float d2 = dx*dx + dy*dy;
+                if (d2 < best_dist) { best_dist = d2; best_idx = i; }
+            }
+            if (best_idx >= 0) {
+                centroid_matched[best_idx] = true;
+                track.x = centroids[best_idx].first;
+                track.y = centroids[best_idx].second;
+                track.missed = 0;
+            } else {
+                track.missed++;
+            }
+        }
+        state.tracks.erase(
+            std::remove_if(state.tracks.begin(), state.tracks.end(),
+                [](const CVTrack& t){ return t.missed > CV_MAX_MISSED; }),
+            state.tracks.end());
+        for (int i = 0; i < (int)centroids.size(); i++) {
+            if (centroid_matched[i]) continue;
+            CVTrack t;
+            t.id      = state.next_id++;
+            t.x       = centroids[i].first;
+            t.y       = centroids[i].second;
+            t.spawn_y = t.y;
+            t.missed  = 0;
+            state.tracks.push_back(t);
+        }
+    } else {
         for (auto& t : state.tracks) t.missed++;
         state.tracks.erase(
             std::remove_if(state.tracks.begin(), state.tracks.end(),
                 [](const CVTrack& t){ return t.missed > CV_MAX_MISSED; }),
             state.tracks.end());
-        return result;
     }
 
-    state.last_motion_frame = state.frame_index;
+    // Event state machine. Refractory period after a fire blocks new events
+    // for CV_EVENT_REFRACTORY_FRAMES frames — absorbs lingering-walker motion
+    // that would otherwise re-trigger a second count.
+    bool in_refractory = state.last_fire_frame != 0 &&
+        (state.frame_index - state.last_fire_frame) < CV_EVENT_REFRACTORY_FRAMES;
 
-    auto centroids = find_centroids(fg);
-
-    std::vector<bool> centroid_matched(centroids.size(), false);
-
-    for (auto& track : state.tracks) {
-        float best_dist = CV_MAX_MOVE * CV_MAX_MOVE;
-        int   best_idx  = -1;
-
-        for (int i = 0; i < (int)centroids.size(); i++) {
-            if (centroid_matched[i]) continue;
-            float dx = centroids[i].first  - track.x;
-            float dy = centroids[i].second - track.y;
-            float d2 = dx*dx + dy*dy;
-            if (d2 < best_dist) { best_dist = d2; best_idx = i; }
+    if (!state.event_active) {
+        if (!in_refractory && fg_count >= CV_EVENT_ENTER_THRESH) {
+            state.event_active      = true;
+            state.event_start_frame = state.frame_index;
+            state.event_frame_count = 1;
+            state.event_peak_n      = fg_count;
+            state.event_first_c     = result.fg_centroid_y;
+            state.event_last_c      = result.fg_centroid_y;
+            state.event_min_c       = result.fg_centroid_y;
+            state.event_max_c       = result.fg_centroid_y;
+            state.event_min_y_seen  = min_y;
+            state.event_max_y_seen  = max_y;
+            state.event_quiet_count = 0;
         }
-
-        if (best_idx >= 0) {
-            centroid_matched[best_idx] = true;
-            track.x = centroids[best_idx].first;
-            track.y = centroids[best_idx].second;
-            track.missed = 0;
+    } else {
+        state.event_frame_count++;
+        if (fg_count > state.event_peak_n) state.event_peak_n = fg_count;
+        if (fg_count > 0) {
+            state.event_last_c = result.fg_centroid_y;
+            if (result.fg_centroid_y < state.event_min_c) state.event_min_c = result.fg_centroid_y;
+            if (result.fg_centroid_y > state.event_max_c) state.event_max_c = result.fg_centroid_y;
+            if (min_y < state.event_min_y_seen) state.event_min_y_seen = min_y;
+            if (max_y > state.event_max_y_seen) state.event_max_y_seen = max_y;
+        }
+        if (fg_count < CV_EVENT_EXIT_THRESH) {
+            state.event_quiet_count++;
+            if (state.event_quiet_count >= CV_EVENT_QUIET_FRAMES) {
+                finalize_event(state, result);
+                event_reset(state);
+                memcpy(state.background, frame, CV_PIXELS);
+            }
         } else {
-            track.missed++;
-        }
-    }
-
-    state.tracks.erase(
-        std::remove_if(state.tracks.begin(), state.tracks.end(),
-            [](const CVTrack& t){ return t.missed > CV_MAX_MISSED; }),
-        state.tracks.end());
-
-    float line_y = (line_pct / 100.0f) * CV_H;
-    for (int i = 0; i < (int)centroids.size(); i++) {
-        if (centroid_matched[i]) continue;
-        CVTrack t;
-        t.id         = state.next_id++;
-        t.x          = centroids[i].first;
-        t.y          = centroids[i].second;
-        t.above_line = (t.y < line_y);
-        t.missed     = 0;
-        state.tracks.push_back(t);
-    }
-    // Line crossing check
-    for (auto& track : state.tracks) {
-        if (track.missed > 0) continue; // only check tracks matched this frame
-        bool now_above = (track.y < line_y);
-        if (now_above != track.above_line) {
-            if (!now_above) {
-                // was above, now below → entry
-                state.entries++;
-                result.entries_delta++;
-            } else {
-                // was below, now above → exit
-                state.exits++;
-                result.exits_delta++;
+            state.event_quiet_count = 0;
+            if (state.event_frame_count > CV_EVENT_MAX_FRAMES) {
+                // Timeout end: fg still elevated. Snap bg anyway — in practice
+                // a stuck-high event means bg is stale (walker has merged
+                // with stale bg, or AEC shifted). Leaving bg stale permanently
+                // poisons subsequent events. If a walker truly is mid-frame
+                // they'll get absorbed into bg, but that's a rare corner
+                // beaten by the common case of stale bg chaining events.
+                finalize_event(state, result);
+                event_reset(state);
+                memcpy(state.background, frame, CV_PIXELS);
             }
         }
-        track.above_line = now_above;
     }
 
     return result;

firmware/lib/cv/cv.h

@@ -12,10 +12,63 @@ static const int CV_MIN_BLOB_PX = 64;
 static const float CV_MAX_MOVE = 15.0f;
 static const int CV_MAX_MISSED = 10;
 
+// Event-based walker detector. Per-frame zone-flip approaches were direction-
+// blind at realistic mounts: a walker traversing top-to-bottom and a walker
+// traversing bottom-to-top produced identical zone-dominance sequences
+// (geometric artifact of asymmetric zones + body spanning the line). The
+// event approach buffers a whole walker event, then decides direction from
+// the centroid trajectory: sign(first_centroid_y - peak_centroid_y) > 0 means
+// the centroid moved upward through the frame during the event.
+//
+// Per-mount convention: UP through frame == ENTRY into store. Flip the camera
+// mount or invert the mapping in cv_process if the physical install differs.
+
+// fg_count thresholds that gate event start/end. Tuned against a real
+// 8-walk isolated test (see .agent/walk_isolated_8walks.log). Lower than
+// initial guesses because the 7' overhead mount produces smaller centroid
+// excursions than we originally modelled.
+static const int CV_EVENT_ENTER_THRESH = 250;
+static const int CV_EVENT_EXIT_THRESH  = 150;
+
+// Number of consecutive sub-EXIT frames required to end an event.
+static const int CV_EVENT_QUIET_FRAMES = 3;
+
+// Min/max event duration in frames. Below min = too brief to be a walker
+// (noise burst). Above max = stationary object or stuck detection.
+static const int CV_EVENT_MIN_FRAMES = 5;
+// MAX bounds the event duration. Too low (15) cut events off while walker
+// was still physically in frame — every fire hit dur=MAX+1 and bg snapped
+// with a walker-ghost baked in, corrupting the next walk. Too high (40)
+// merged multiple walkers. 25 frames (5s) lets a single walker reach the
+// quiet-exit path (fg drops below EXIT_THRESH) before timeout, so bg snaps
+// on a clean empty frame.
+static const int CV_EVENT_MAX_FRAMES = 25;
+
+// Required vertical extent: during the event, fg must have reached near the
+// top of the frame (min_y <= TOP) AND near the bottom (max_y >= BOT). At a
+// 7' overhead mount real walkers span fg y≈0..70, not 0..95 — the original
+// 10/85 gates rejected most real walks. Relaxed to catch them while still
+// filtering small local motion that doesn't span the doorway.
+static const int CV_EVENT_EXTENT_TOP = 25;
+static const int CV_EVENT_EXTENT_BOT = 50;
+
+// Minimum centroid excursion (max of up_score/down_score) for a valid
+// trajectory. At overhead mount walker centroid traverses ~15-40 pixels;
+// 15 was too aggressive and dropped clean walks. 5 still filters wobble.
+static const float CV_EVENT_MIN_TRAJ = 5.0f;
+
+// Refractory period after a fire. Shorter than originally chosen — at 5 fps
+// a second walker can arrive within 2s of the first, especially at busy
+// doorways. 10 frames = 2s of back-pressure, tuned to match the gap between
+// consecutive isolated walks in the test log.
+static const uint32_t CV_EVENT_REFRACTORY_FRAMES = 10;
+
+// Diagnostic only: tracks are kept for spawn logging. Counting does NOT
+// depend on tracks.
 struct CVTrack {
     int   id;
     float x, y;
-    bool  above_line;
+    float spawn_y;
     int   missed;
 };
 
@@ -28,11 +81,36 @@ struct CVState {
     std::vector<CVTrack> tracks;
     int entries;
     int exits;
+
+    // Event state machine.
+    bool     event_active;
+    uint32_t event_start_frame;
+    int      event_frame_count;
+    int      event_peak_n;
+    float    event_first_c;
+    float    event_last_c;
+    float    event_min_c;        // min centroid_y observed during event
+    float    event_max_c;        // max centroid_y observed during event
+    int      event_min_y_seen;
+    int      event_max_y_seen;
+    int      event_quiet_count;
+    uint32_t last_fire_frame;    // 0 = never; frame of last counted fire
 };
 
 struct CVResult {
     int entries_delta;
     int exits_delta;
+    // Per-frame foreground diagnostics (populated every call).
+    int   fg_count;
+    int   fg_min_y;
+    int   fg_max_y;
+    float fg_centroid_y;
+    // Populated only on a fire frame; zeroed otherwise.
+    float fire_first_c;
+    float fire_min_c;
+    float fire_max_c;
+    float fire_last_c;
+    int   fire_duration;
 };
 
 void cv_init(CVState& state);

firmware/platformio.ini

@@ -7,6 +7,7 @@ platform = espressif32@6.6.0
 board = m5stack-timer-cam
 framework = arduino
 board_build.partitions = partitions_4mb_ota.csv
+build_src_filter = +<*> -<main_capture.cpp>
 build_flags =
     -DBOARD_HAS_PSRAM
     -mfix-esp32-psram-cache-issue
@@ -23,6 +24,25 @@ lib_deps =
     h2zero/NimBLE-Arduino@^1.4.2
     espressif/esp32-camera
 
+; Frame-capture build. Strips WiFi/BLE/CV/reporter; streams raw 96x96 frames
+; over serial at 921600 baud for offline algorithm iteration.
+[env:timercam-capture]
+platform = espressif32@6.6.0
+board = m5stack-timer-cam
+framework = arduino
+board_build.partitions = partitions_4mb_ota.csv
+build_flags =
+    -DBOARD_HAS_PSRAM
+    -mfix-esp32-psram-cache-issue
+    -DCORE_DEBUG_LEVEL=0
+    -DCONFIG_SPIRAM_USE_MALLOC=1
+build_src_filter = -<*> +<main_capture.cpp> +<camera.cpp>
+monitor_speed = 460800
+upload_speed = 115200
+upload_flags = --no-stub
+lib_deps =
+    espressif/esp32-camera
+
 [env:native]
 platform = native
 test_framework = unity

firmware/src/main.cpp

@@ -24,9 +24,22 @@ static DeviceConfig     g_cfg;
 static CVState          g_cv;
 static SemaphoreHandle_t s_cv_mutex = nullptr;
 
-// LED: simple on/off — blink patterns can be added later
 static void led_set(bool on) { digitalWrite(LED_PIN, on ? HIGH : LOW); }
 
+// Non-blocking-ish detection blink. Saves and restores the current LED state
+// so it doesn't clobber upload/no-wifi indicators. Total duration: ~60ms per
+// pulse + 80ms gap between pulses.
+static void led_blink_pattern(int pulses) {
+    bool prev = digitalRead(LED_PIN);
+    for (int i = 0; i < pulses; i++) {
+        led_set(true);
+        vTaskDelay(pdMS_TO_TICKS(60));
+        led_set(false);
+        if (i < pulses - 1) vTaskDelay(pdMS_TO_TICKS(80));
+    }
+    led_set(prev);
+}
+
 static void check_factory_reset() {
     if (digitalRead(BUTTON_PIN) != LOW) return;
     uint32_t held = millis();
@@ -42,13 +55,30 @@ static void check_factory_reset() {
 // Camera + CV task — runs on core 1 at 5 fps
 static void task_camera(void*) {
     static uint8_t frame[CV_PIXELS];  // static: avoids 9KB on task stack
+    int last_logged_track_id = 0;     // diagnostic: log each new track once
     while (true) {
         if (camera_capture_96(frame)) {
             if (xSemaphoreTake(s_cv_mutex, pdMS_TO_TICKS(100)) == pdTRUE) {
                 CVResult r = cv_process(g_cv, frame, g_cfg.line_offset);
-                if (r.entries_delta) Serial.printf("[CV] entry +%d (total %d)\n", r.entries_delta, g_cv.entries);
-                if (r.exits_delta)   Serial.printf("[CV] exit  +%d (total %d)\n", r.exits_delta,  g_cv.exits);
+                for (const auto& t : g_cv.tracks) {
+                    if (t.id > last_logged_track_id) {
+                        last_logged_track_id = t.id;
+                        Serial.printf("[CV] spawn id=%d y=%.1f\n", t.id, t.spawn_y);
+                    }
+                }
+                if (r.fg_count > 0) {
+                    Serial.printf("[F] n=%d y=%d..%d c=%.1f\n",
+                        r.fg_count, r.fg_min_y, r.fg_max_y, r.fg_centroid_y);
+                }
+                if (r.entries_delta) Serial.printf("[CV] entry +%d (total %d) first=%.1f min=%.1f max=%.1f last=%.1f dur=%d\n",
+                    r.entries_delta, g_cv.entries,
+                    r.fire_first_c, r.fire_min_c, r.fire_max_c, r.fire_last_c, r.fire_duration);
+                if (r.exits_delta)   Serial.printf("[CV] exit  +%d (total %d) first=%.1f min=%.1f max=%.1f last=%.1f dur=%d\n",
+                    r.exits_delta,  g_cv.exits,
+                    r.fire_first_c, r.fire_min_c, r.fire_max_c, r.fire_last_c, r.fire_duration);
                 xSemaphoreGive(s_cv_mutex);
+                if (r.entries_delta) led_blink_pattern(1);
+                if (r.exits_delta)   led_blink_pattern(2);
             }
         }
         vTaskDelay(pdMS_TO_TICKS(CAM_INTERVAL_MS));

firmware/src/main_capture.cpp

@@ -0,0 +1,64 @@
+// firmware/src/main_capture.cpp
+//
+// Frame-dump firmware. Replaces main.cpp when building env:timercam-capture.
+// Streams raw 96x96 grayscale frames at 5 fps over serial (921600 baud) for
+// offline algorithm iteration.
+//
+// Wire format per frame (little-endian):
+//   magic    uint32  0xDC0FC0DE
+//   frame_ix uint32  monotonic counter
+//   millis   uint32  ms since boot
+//   pixels   byte[9216]  raw grayscale 96x96, row-major
+//
+// No WiFi, no BLE, no CV. Just camera → serial.
+
+#include <Arduino.h>
+#include "camera.h"
+#include "cv.h"  // for CV_PIXELS
+
+#define LED_PIN 2
+#define CAM_FPS 5
+#define CAM_INTERVAL_MS (1000 / CAM_FPS)
+
+// Magic chosen from bytes that commonly survive; 'FRM1' ascii.
+// Avoid high bytes 0xA0-AF / 0xD0-DF — observed missing from the CH9102 stream.
+static const uint32_t FRAME_MAGIC = 0x314D5246; // 'FRM1' little-endian on wire
+
+void setup() {
+    Serial.begin(460800);
+    pinMode(LED_PIN, OUTPUT);
+    digitalWrite(LED_PIN, HIGH);
+
+    delay(500);
+    Serial.println("# capture-mode: 460800 baud, 96x96 gray @ 5fps");
+    Serial.flush();
+
+    if (!camera_init()) {
+        Serial.println("# FATAL: camera init failed");
+        while (true) {
+            digitalWrite(LED_PIN, !digitalRead(LED_PIN));
+            delay(200);
+        }
+    }
+
+    digitalWrite(LED_PIN, LOW);
+}
+
+void loop() {
+    static uint8_t frame[CV_PIXELS];
+    static uint32_t frame_ix = 0;
+    uint32_t t0 = millis();
+
+    if (camera_capture_96(frame)) {
+        uint32_t ms = millis();
+        Serial.write((uint8_t*)&FRAME_MAGIC, 4);
+        Serial.write((uint8_t*)&frame_ix,    4);
+        Serial.write((uint8_t*)&ms,          4);
+        Serial.write(frame, CV_PIXELS);
+        frame_ix++;
+        digitalWrite(LED_PIN, frame_ix & 1);
+    }
+
+    uint32_t elapsed = millis() - t0;
+    if (elapsed < CAM_INTERVAL_MS) delay(CAM_INTERVAL_MS - elapsed);
+}

firmware/test/test_cv/test_cv.cpp

@@ -7,160 +7,290 @@ static void fill_frame(uint8_t* f, uint8_t val) {
     memset(f, val, CV_PIXELS);
 }
 
+// Draw a rectangular walker-blob spanning rows [y0, y1], columns [cx-hw, cx+hw].
+// Pixel value 200 over background 100 -> frame_diff threshold (30) is cleared.
+static void draw_walker(uint8_t* f, int y0, int y1, int cx, int hw) {
+    fill_frame(f, 100);
+    for (int y = y0; y <= y1; y++) {
+        if (y < 0 || y >= CV_H) continue;
+        for (int x = cx - hw; x <= cx + hw; x++) {
+            if (x < 0 || x >= CV_W) continue;
+            f[y * CV_W + x] = 200;
+        }
+    }
+}
+
+static void prime_bg(CVState& state) {
+    uint8_t bg[CV_PIXELS];
+    fill_frame(bg, 100);
+    cv_process(state, bg, 50);
+}
+
+// Let the event state machine see QUIET_FRAMES+1 empty frames so any active
+// event finalizes before the next test assertion.
+static void quiesce(CVState& state) {
+    uint8_t bg[CV_PIXELS]; fill_frame(bg, 100);
+    for (int i = 0; i < CV_EVENT_QUIET_FRAMES + 1; i++) cv_process(state, bg, 50);
+}
+
 void setUp(void) {}
 void tearDown(void) {}
 
-void test_frame_diff_no_change_gives_no_fg() {
-    CVState state;
-    cv_init(state);
-
-    uint8_t frame[CV_PIXELS];
-    fill_frame(frame, 128);
-
+void test_no_change_no_event() {
+    CVState state; cv_init(state);
+    uint8_t frame[CV_PIXELS]; fill_frame(frame, 128);
     CVResult r1 = cv_process(state, frame, 50);
     TEST_ASSERT_EQUAL_INT(0, r1.entries_delta);
-
     CVResult r2 = cv_process(state, frame, 50);
     TEST_ASSERT_EQUAL_INT(0, r2.entries_delta);
     TEST_ASSERT_EQUAL_INT(0, r2.exits_delta);
 }
 
-void test_frame_diff_large_change_detected_no_crash() {
-    CVState state;
-    cv_init(state);
-
-    uint8_t bg[CV_PIXELS], fg_frame[CV_PIXELS];
-    fill_frame(bg, 100);
-    fill_frame(fg_frame, 200);
-
-    cv_process(state, bg, 50);
-    CVResult r = cv_process(state, fg_frame, 50);
-
-    // Tracking not yet implemented — just verify no crash and result is zero
-    TEST_ASSERT_EQUAL_INT(0, r.entries_delta);
-    TEST_ASSERT_EQUAL_INT(0, r.exits_delta);
-}
-
 void test_cv_init_clears_state() {
     CVState state;
-    state.entries = 99; state.exits = 88;
+    state.entries = 99; state.exits = 88; state.event_active = true;
     cv_init(state);
     TEST_ASSERT_EQUAL_INT(0, state.entries);
     TEST_ASSERT_EQUAL_INT(0, state.exits);
     TEST_ASSERT_FALSE(state.bg_valid);
+    TEST_ASSERT_FALSE(state.event_active);
 }
 
 void test_cv_reset_counts() {
-    CVState state;
-    cv_init(state);
-    state.entries = 5;
-    state.exits   = 3;
+    CVState state; cv_init(state);
+    state.entries = 5; state.exits = 3;
     cv_reset_counts(state);
     TEST_ASSERT_EQUAL_INT(0, state.entries);
     TEST_ASSERT_EQUAL_INT(0, state.exits);
 }
 
-void test_tracking_spawns_track_for_new_blob() {
-    CVState state;
-    cv_init(state);
+void test_walker_up_through_frame_is_entry() {
+    // Simulate a walker traversing from bottom to top of frame.
+    // Per-frame fg_count and centroid (11-wide column, height H -> n=11*H):
+    //   t0 y=60..95 n=396 c=77   <- event starts (n >= ENTER=300)
+    //   t1 y=30..95 n=726 c=62
+    //   t2 y=0..95  n=1056 c=47
+    //   t3 y=0..60  n=671 c=30
+    //   t4 y=0..25  n=286 c=12   (below EXIT=200, quiet=1)
+    //   t5 y=0..10  n=121 c=5    (below EXIT, quiet=2)
+    //   t6 empty                  quiet=3 -> finalize
+    CVState state; cv_init(state);
+    prime_bg(state);
 
-    uint8_t bg[CV_PIXELS];
-    fill_frame(bg, 100);
-    cv_process(state, bg, 50); // init background
-
-    // Frame with a bright 30x30 blob in top-left quadrant
-    uint8_t blob_frame[CV_PIXELS];
-    fill_frame(blob_frame, 100);
-    for (int y = 5; y < 35; y++)
-        for (int x = 5; x < 35; x++)
-            blob_frame[y * CV_W + x] = 200;
-
-    cv_process(state, blob_frame, 50);
-
-    TEST_ASSERT_EQUAL_INT(1, (int)state.tracks.size());
-    TEST_ASSERT_FLOAT_WITHIN(5.0f, 20.0f, state.tracks[0].x);
-    TEST_ASSERT_FLOAT_WITHIN(5.0f, 20.0f, state.tracks[0].y);
-}
-
-static void make_blob_frame(uint8_t* f, int cx, int cy) {
-    fill_frame(f, 100);
-    for (int y = cy - 12; y <= cy + 12; y++)
-        for (int x = cx - 12; x <= cx + 12; x++)
-            if (y >= 0 && y < CV_H && x >= 0 && x < CV_W)
-                f[y * CV_W + x] = 200;
-}
-
-void test_blob_crossing_line_top_to_bottom_is_entry() {
-    CVState state;
-    cv_init(state);
-
-    // Line at 50% = y=48; step ≤14px per frame to stay within CV_MAX_MOVE
-    uint8_t bg[CV_PIXELS];
-    fill_frame(bg, 100);
-    cv_process(state, bg, 50); // init background
-
-    // Walk blob from y=20 toward line; crossing occurs at y=48 (above→below)
-    // Stop at crossing frame and assert its result
-    int setup[] = {20, 34};
-    for (int i = 0; i < 2; i++) {
-        uint8_t f[CV_PIXELS]; make_blob_frame(f, 48, setup[i]);
+    int rows[][2] = {{60,95},{30,95},{0,95},{0,60},{0,25},{0,10}};
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
         cv_process(state, f, 50);
     }
-    uint8_t fcross[CV_PIXELS]; make_blob_frame(fcross, 48, 48);
-    CVResult r = cv_process(state, fcross, 50);
+    quiesce(state);
 
-    TEST_ASSERT_EQUAL_INT(1, r.entries_delta);
-    TEST_ASSERT_EQUAL_INT(0, r.exits_delta);
+    TEST_ASSERT_EQUAL_INT(1, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+}
+
+void test_walker_down_through_frame_is_exit() {
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    int rows[][2] = {{0,35},{0,65},{0,95},{35,95},{70,95},{85,95}};
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(1, state.exits);
+}
+
+void test_approach_retreat_without_full_extent_does_not_fire() {
+    // Walker approaches from bottom, reaches y=30, retreats, never reaches top.
+    // Extent gate requires min_y_seen <= 10; this event tops out at y=30 so
+    // extent never clears and no fire occurs regardless of trajectory score.
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    int rows[][2] = {{60,95},{40,95},{30,95},{40,95},{60,95},{80,95}};
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+}
+
+void test_brief_burst_below_min_duration_does_not_fire() {
+    // One frame of large fg, then gone. Event starts, immediately quiesces,
+    // duration ends up below CV_EVENT_MIN_FRAMES.
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    uint8_t f[CV_PIXELS]; draw_walker(f, 0, 95, 48, 5);
+    cv_process(state, f, 50);
+    quiesce(state);
+
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+}
+
+void test_stationary_large_blob_does_not_fire() {
+    // Static large blob in frame for many frames, then removed. Centroid
+    // never moves -> MIN_TRAJ gate blocks fire.
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    for (int i = 0; i < 10; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, 0, 95, 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+}
+
+// Wait out the refractory period with bg-only frames so the next walker
+// event is accepted.
+static void wait_refractory(CVState& state) {
+    uint8_t bg[CV_PIXELS]; fill_frame(bg, 100);
+    for (uint32_t i = 0; i < CV_EVENT_REFRACTORY_FRAMES + 2; i++) {
+        cv_process(state, bg, 50);
+    }
+}
+
+void test_two_sequential_walkers_count_twice() {
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    int rows[][2] = {{60,95},{30,95},{0,95},{0,60},{0,25},{0,10}};
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+    wait_refractory(state);
+
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+
+    TEST_ASSERT_EQUAL_INT(2, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
+}
+
+void test_full_reversal_counts_entry_then_exit() {
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    int up_rows[][2]   = {{60,95},{30,95},{0,95},{0,60},{0,25},{0,10}};
+    int down_rows[][2] = {{0,35},{0,65},{0,95},{35,95},{70,95},{85,95}};
+
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, up_rows[i][0], up_rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+    wait_refractory(state);
+
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, down_rows[i][0], down_rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+
+    TEST_ASSERT_EQUAL_INT(1, state.entries);
+    TEST_ASSERT_EQUAL_INT(1, state.exits);
+}
+
+void test_refractory_suppresses_back_to_back_fire() {
+    // After a fire, a second event attempted within CV_EVENT_REFRACTORY_FRAMES
+    // is suppressed. Simulates walker lingering / ghost re-triggering.
+    CVState state; cv_init(state);
+    prime_bg(state);
+
+    int rows[][2] = {{60,95},{30,95},{0,95},{0,60},{0,25},{0,10}};
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+    TEST_ASSERT_EQUAL_INT(1, state.entries);
+
+    // Immediate second walker within refractory window — should NOT count.
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
     TEST_ASSERT_EQUAL_INT(1, state.entries);
 }
 
-void test_blob_crossing_line_bottom_to_top_is_exit() {
-    CVState state;
-    cv_init(state);
+void test_event_counts_after_refractory_expires() {
+    CVState state; cv_init(state);
+    prime_bg(state);
 
-    uint8_t bg[CV_PIXELS]; fill_frame(bg, 100);
-    cv_process(state, bg, 50);
-
-    // Walk blob from y=76 toward line; crossing occurs at y=34 (below→above)
-    // Stop at crossing frame and assert its result
-    int setup[] = {76, 62, 48};
-    for (int i = 0; i < 3; i++) {
-        uint8_t f[CV_PIXELS]; make_blob_frame(f, 48, setup[i]);
+    int rows[][2] = {{60,95},{30,95},{0,95},{0,60},{0,25},{0,10}};
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
         cv_process(state, f, 50);
     }
-    uint8_t fcross[CV_PIXELS]; make_blob_frame(fcross, 48, 34);
-    CVResult r = cv_process(state, fcross, 50);
+    quiesce(state);
+    TEST_ASSERT_EQUAL_INT(1, state.entries);
 
-    TEST_ASSERT_EQUAL_INT(0, r.entries_delta);
-    TEST_ASSERT_EQUAL_INT(1, r.exits_delta);
+    // Wait out the refractory period.
+    uint8_t bg[CV_PIXELS]; fill_frame(bg, 100);
+    for (uint32_t i = 0; i < CV_EVENT_REFRACTORY_FRAMES + 2; i++) {
+        cv_process(state, bg, 50);
+    }
+
+    // Second walker — should now count.
+    for (int i = 0; i < 6; i++) {
+        uint8_t f[CV_PIXELS]; draw_walker(f, rows[i][0], rows[i][1], 48, 5);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
+    TEST_ASSERT_EQUAL_INT(2, state.entries);
 }
 
-void test_no_crossing_same_side_no_count() {
-    CVState state;
-    cv_init(state);
+void test_noise_below_enter_thresh_does_not_start_event() {
+    // Tiny 5x5 blob (25 px) never crosses ENTER=300, event never starts.
+    CVState state; cv_init(state);
+    prime_bg(state);
 
-    uint8_t bg[CV_PIXELS]; fill_frame(bg, 100);
-    cv_process(state, bg, 50);
+    auto small = [](uint8_t* f, int cy) {
+        fill_frame(f, 100);
+        for (int y = cy-2; y <= cy+2; y++)
+            for (int x = 46; x <= 50; x++)
+                if (y>=0 && y<CV_H && x>=0 && x<CV_W) f[y*CV_W+x] = 200;
+    };
+    for (int cy = 10; cy <= 90; cy += 8) {
+        uint8_t f[CV_PIXELS]; small(f, cy);
+        cv_process(state, f, 50);
+    }
+    quiesce(state);
 
-    uint8_t f1[CV_PIXELS]; make_blob_frame(f1, 48, 20); // above line
-    cv_process(state, f1, 50);
-
-    uint8_t f2[CV_PIXELS]; make_blob_frame(f2, 48, 30); // still above line, moved closer
-    CVResult r = cv_process(state, f2, 50);
-
-    TEST_ASSERT_EQUAL_INT(0, r.entries_delta);
-    TEST_ASSERT_EQUAL_INT(0, r.exits_delta);
+    TEST_ASSERT_EQUAL_INT(0, state.entries);
+    TEST_ASSERT_EQUAL_INT(0, state.exits);
 }
 
 int main() {
     UNITY_BEGIN();
-    RUN_TEST(test_frame_diff_no_change_gives_no_fg);
-    RUN_TEST(test_frame_diff_large_change_detected_no_crash);
+    RUN_TEST(test_no_change_no_event);
     RUN_TEST(test_cv_init_clears_state);
     RUN_TEST(test_cv_reset_counts);
-    RUN_TEST(test_tracking_spawns_track_for_new_blob);
-    RUN_TEST(test_blob_crossing_line_top_to_bottom_is_entry);
-    RUN_TEST(test_blob_crossing_line_bottom_to_top_is_exit);
-    RUN_TEST(test_no_crossing_same_side_no_count);
+    RUN_TEST(test_walker_up_through_frame_is_entry);
+    RUN_TEST(test_walker_down_through_frame_is_exit);
+    RUN_TEST(test_approach_retreat_without_full_extent_does_not_fire);
+    RUN_TEST(test_brief_burst_below_min_duration_does_not_fire);
+    RUN_TEST(test_stationary_large_blob_does_not_fire);
+    RUN_TEST(test_two_sequential_walkers_count_twice);
+    RUN_TEST(test_full_reversal_counts_entry_then_exit);
+    RUN_TEST(test_refractory_suppresses_back_to_back_fire);
+    RUN_TEST(test_event_counts_after_refractory_expires);
+    RUN_TEST(test_noise_below_enter_thresh_does_not_start_event);
     return UNITY_END();
 }

tools/capture_frames.py

@@ -0,0 +1,105 @@
+#!/usr/bin/env python3
+# tools/capture_frames.py
+#
+# Read framed 96x96 grayscale frames from the capture-mode firmware over serial
+# and write them to a .bin file for offline replay.
+#
+# Wire format per frame (little-endian):
+#   magic    u32  0xDC0FC0DE
+#   frame_ix u32
+#   millis   u32
+#   pixels   9216 bytes
+#
+# Output file is the raw concatenation of frames (same layout as the wire),
+# so replay_frames.py can stream it with identical parsing.
+#
+# Usage: python tools/capture_frames.py --port /dev/ttyUSB0 --out walk.bin --duration 60
+
+import argparse
+import serial
+import struct
+import sys
+import time
+
+MAGIC = 0x314D5246  # 'FRM1' — ascii bytes that survive the CH9102 stream
+FRAME_PIXELS = 96 * 96
+HEADER_LEN = 12
+FRAME_LEN = HEADER_LEN + FRAME_PIXELS
+
+
+def read_exact(ser, n):
+    buf = bytearray()
+    while len(buf) < n:
+        chunk = ser.read(n - len(buf))
+        if not chunk:
+            return None
+        buf.extend(chunk)
+    return bytes(buf)
+
+
+def find_magic(ser):
+    """Scan serial byte-by-byte until we see the 4-byte MAGIC."""
+    window = bytearray()
+    magic_bytes = struct.pack('<I', MAGIC)
+    while True:
+        b = ser.read(1)
+        if not b:
+            return False
+        window.extend(b)
+        if len(window) > 4:
+            del window[0]
+        if bytes(window) == magic_bytes:
+            return True
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument('--port', required=True)
+    ap.add_argument('--baud', type=int, default=460800)
+    ap.add_argument('--out',  required=True)
+    ap.add_argument('--duration', type=float, default=60.0,
+                    help='Seconds to capture (default 60)')
+    args = ap.parse_args()
+
+    ser = serial.Serial(args.port, args.baud, timeout=1.0)
+    print(f'# listening on {args.port} @ {args.baud} for {args.duration}s...',
+          file=sys.stderr)
+
+    # Drain boot banner lines.
+    deadline_banner = time.time() + 2.0
+    while time.time() < deadline_banner:
+        line = ser.readline()
+        if line.startswith(b'#'):
+            print(line.decode(errors='replace').rstrip(), file=sys.stderr)
+        if b'capture-mode' in line:
+            break
+
+    deadline = time.time() + args.duration
+    frames = 0
+    last_ix = None
+    dropped = 0
+
+    with open(args.out, 'wb') as f:
+        while time.time() < deadline:
+            if not find_magic(ser):
+                continue
+            body = read_exact(ser, 8 + FRAME_PIXELS)
+            if body is None:
+                break
+            frame_ix, ms = struct.unpack('<II', body[:8])
+            if last_ix is not None and frame_ix != last_ix + 1:
+                dropped += frame_ix - last_ix - 1
+            last_ix = frame_ix
+            f.write(struct.pack('<I', MAGIC))
+            f.write(body)
+            frames += 1
+            if frames % 25 == 0:
+                print(f'# {frames} frames, last ix={frame_ix} ms={ms} '
+                      f'dropped={dropped}', file=sys.stderr)
+
+    print(f'# done: {frames} frames written to {args.out} '
+          f'({dropped} dropped)', file=sys.stderr)
+
+
+if __name__ == '__main__':
+    main()

tools/replay_frames.py

@@ -0,0 +1,211 @@
+#!/usr/bin/env python3
+# tools/replay_frames.py
+#
+# Offline Python port of the event-based CV detector (firmware/lib/cv/cv.cpp).
+# Reads a .bin file produced by capture_frames.py and prints events.
+#
+# Purpose: iterate algorithm changes in seconds instead of minutes. All
+# constants match cv.h so baseline behavior matches firmware.
+#
+# Usage:
+#   python tools/replay_frames.py walk.bin
+#   python tools/replay_frames.py walk.bin --enter 250 --exit 150 --max 25
+#
+# Output: one line per frame with fg diagnostics, plus [ENTRY]/[EXIT] lines
+# when the detector fires.
+
+import argparse
+import struct
+import sys
+
+import numpy as np
+
+MAGIC = 0x314D5246  # 'FRM1'
+W = H = 96
+PIXELS = W * H
+HEADER = 12
+FRAME_LEN = HEADER + PIXELS
+
+
+class Detector:
+    """Mirror of firmware CV state machine. Single walker events, centroid
+    trajectory direction. Only per-frame fg_count + min/max y + centroid y
+    feed the decision — per-blob tracks are diagnostic in firmware, dropped
+    here."""
+
+    def __init__(self, args):
+        self.a = args
+        self.bg = None
+        self.ev_active = False
+        self.ev_frames = 0
+        self.ev_first_c = -1.0
+        self.ev_last_c  = -1.0
+        self.ev_min_c   = float(H)
+        self.ev_max_c   = -1.0
+        self.ev_min_y   = H
+        self.ev_max_y   = -1
+        self.ev_quiet   = 0
+        self.last_fire  = 0
+        self.frame_ix   = 0
+        self.entries    = 0
+        self.exits      = 0
+
+    def _reset_event(self):
+        self.ev_active = False
+        self.ev_frames = 0
+        self.ev_first_c = self.ev_last_c = -1.0
+        self.ev_min_c = float(H)
+        self.ev_max_c = -1.0
+        self.ev_min_y = H
+        self.ev_max_y = -1
+        self.ev_quiet = 0
+
+    def _finalize(self):
+        a = self.a
+        if self.ev_frames < a.min_frames: return None
+        if self.ev_min_y  > a.extent_top: return None
+        if self.ev_max_y  < a.extent_bot: return None
+        up   = self.ev_first_c - self.ev_min_c
+        down = self.ev_max_c   - self.ev_first_c
+        winning = max(up, down)
+        if winning < a.min_traj: return None
+        is_entry = up >= down
+        self.last_fire = self.frame_ix
+        info = dict(
+            kind='ENTRY' if is_entry else 'EXIT',
+            first=self.ev_first_c, min=self.ev_min_c,
+            max=self.ev_max_c, last=self.ev_last_c,
+            dur=self.ev_frames,
+        )
+        if is_entry: self.entries += 1
+        else:        self.exits   += 1
+        return info
+
+    def step(self, frame):
+        """frame: uint8 array of shape (H, W). Returns list of fire dicts."""
+        self.frame_ix += 1
+        fires = []
+
+        if self.bg is None:
+            self.bg = frame.astype(np.int16)
+            return fires
+
+        bg = self.bg.astype(np.int16)
+        diff = np.abs(frame.astype(np.int16) - bg)
+        fg = (diff > self.a.diff_thresh).astype(np.uint8)
+
+        # Running-avg bg blend, frozen during active event.
+        if not self.ev_active:
+            self.bg = ((self.bg * 31 + frame.astype(np.int16)) >> 5)
+
+        fg_count = int(fg.sum())
+        if fg_count > 0:
+            row_counts = fg.sum(axis=1)
+            ys = np.where(row_counts > 0)[0]
+            min_y = int(ys.min())
+            max_y = int(ys.max())
+            centroid_y = float((row_counts * np.arange(H)).sum() / fg_count)
+        else:
+            min_y, max_y, centroid_y = -1, -1, -1.0
+
+        # Self-heal on catastrophic bg mismatch.
+        if fg_count > PIXELS // 2:
+            self.bg = frame.astype(np.int16)
+            if self.ev_active: self._reset_event()
+            return fires
+
+        a = self.a
+        in_refractory = (self.last_fire != 0 and
+                         (self.frame_ix - self.last_fire) < a.refractory)
+
+        if not self.ev_active:
+            if not in_refractory and fg_count >= a.enter_thresh:
+                self.ev_active  = True
+                self.ev_frames  = 1
+                self.ev_first_c = centroid_y
+                self.ev_last_c  = centroid_y
+                self.ev_min_c   = centroid_y
+                self.ev_max_c   = centroid_y
+                self.ev_min_y   = min_y
+                self.ev_max_y   = max_y
+                self.ev_quiet   = 0
+        else:
+            self.ev_frames += 1
+            if fg_count > 0:
+                self.ev_last_c = centroid_y
+                if centroid_y < self.ev_min_c: self.ev_min_c = centroid_y
+                if centroid_y > self.ev_max_c: self.ev_max_c = centroid_y
+                if min_y < self.ev_min_y: self.ev_min_y = min_y
+                if max_y > self.ev_max_y: self.ev_max_y = max_y
+
+            ended = False
+            if fg_count < a.exit_thresh:
+                self.ev_quiet += 1
+                if self.ev_quiet >= a.quiet_frames:
+                    ended = True
+            else:
+                self.ev_quiet = 0
+                if self.ev_frames > a.max_frames:
+                    ended = True
+
+            if ended:
+                fire = self._finalize()
+                if fire: fires.append(fire)
+                self._reset_event()
+                self.bg = frame.astype(np.int16)
+
+        return fires, fg_count, min_y, max_y, centroid_y
+
+
+def iter_frames(path):
+    with open(path, 'rb') as f:
+        data = f.read()
+    n = len(data) // FRAME_LEN
+    for i in range(n):
+        off = i * FRAME_LEN
+        magic, ix, ms = struct.unpack('<III', data[off:off + HEADER])
+        if magic != MAGIC:
+            raise RuntimeError(f'bad magic at frame {i}: 0x{magic:08x}')
+        frame = np.frombuffer(data, dtype=np.uint8,
+                              count=PIXELS, offset=off + HEADER).reshape(H, W)
+        yield ix, ms, frame
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument('path')
+    ap.add_argument('--diff-thresh', dest='diff_thresh', type=int, default=30)
+    ap.add_argument('--enter', dest='enter_thresh', type=int, default=300)
+    ap.add_argument('--exit',  dest='exit_thresh',  type=int, default=200)
+    ap.add_argument('--quiet', dest='quiet_frames', type=int, default=3)
+    ap.add_argument('--min',   dest='min_frames',   type=int, default=5)
+    ap.add_argument('--max',   dest='max_frames',   type=int, default=25)
+    ap.add_argument('--extent-top', dest='extent_top', type=int, default=10)
+    ap.add_argument('--extent-bot', dest='extent_bot', type=int, default=85)
+    ap.add_argument('--min-traj', dest='min_traj', type=float, default=15.0)
+    ap.add_argument('--refractory', dest='refractory', type=int, default=15)
+    ap.add_argument('--quiet-log', action='store_true',
+                    help='Suppress per-frame fg lines')
+    args = ap.parse_args()
+
+    det = Detector(args)
+    total = 0
+    for ix, ms, frame in iter_frames(args.path):
+        total += 1
+        out = det.step(frame)
+        if out == []:
+            if not args.quiet_log:
+                print(f'[{ix:4d}] bg init')
+            continue
+        fires, fg, miny, maxy, cy = out
+        if not args.quiet_log and fg > 0:
+            print(f'[{ix:4d}] n={fg:4d} y={miny:2d}..{maxy:2d} c={cy:5.1f}')
+        for fire in fires:
+            print(f'  >>> {fire["kind"]} first={fire["first"]:.1f} '
+                  f'min={fire["min"]:.1f} max={fire["max"]:.1f} '
+                  f'last={fire["last"]:.1f} dur={fire["dur"]}')
+    print(f'\n# {total} frames  entries={det.entries}  exits={det.exits}')
+
+
+if __name__ == '__main__':
+    main()

tools/replay_logs.py

@@ -0,0 +1,186 @@
+#!/usr/bin/env python3
+# tools/replay_logs.py
+#
+# Replay the event state machine against text serial logs captured from the
+# production firmware. Input lines of the form:
+#   [F] n=<fg_count> y=<min_y>..<max_y> c=<centroid_y>
+#
+# Those four values are exactly what the firmware's event state machine
+# consumes — so we can iterate event-level params (thresholds, max_frames,
+# extent gates, trajectory cutoffs, refractory) offline without needing raw
+# frames or the device.
+#
+# Usage:
+#   python tools/replay_logs.py walk.log
+#   python tools/replay_logs.py walk.log --enter 250 --exit 100 --max 30 --min-traj 10
+#   cat walk.log | python tools/replay_logs.py - --ground-truth 12
+
+import argparse
+import re
+import sys
+
+
+LINE_RE = re.compile(
+    r'\[F\]\s+n=(?P<n>\d+)\s+y=(?P<miny>-?\d+)\.\.(?P<maxy>-?\d+)\s+c=(?P<c>-?\d+\.\d+)'
+)
+
+
+def parse_frames(text):
+    """Yield (fg_count, min_y, max_y, centroid_y) per [F] line, in order."""
+    for line in text.splitlines():
+        m = LINE_RE.search(line)
+        if not m:
+            continue
+        yield int(m['n']), int(m['miny']), int(m['maxy']), float(m['c'])
+
+
+class Detector:
+    """Mirror of firmware event state machine. Only uses per-frame diagnostic
+    values — the same inputs the firmware feeds it."""
+
+    def __init__(self, a):
+        self.a = a
+        self.ev = False
+        self.ev_n = 0
+        self.ev_first = self.ev_last = -1.0
+        self.ev_min = 1e9
+        self.ev_max = -1.0
+        self.ev_miny = 1e9
+        self.ev_maxy = -1
+        self.ev_quiet = 0
+        self.last_fire = -10**9
+        self.ix = 0
+        self.entries = 0
+        self.exits = 0
+        self.fires = []
+
+    def _reset(self):
+        self.ev = False
+        self.ev_n = 0
+        self.ev_first = self.ev_last = -1.0
+        self.ev_min = 1e9; self.ev_max = -1.0
+        self.ev_miny = 1e9; self.ev_maxy = -1
+        self.ev_quiet = 0
+
+    def _finalize(self):
+        a = self.a
+        if self.ev_n < a.min_frames:
+            return ('reject_short', None)
+        if self.ev_miny > a.extent_top:
+            return ('reject_extent_top', None)
+        if self.ev_maxy < a.extent_bot:
+            return ('reject_extent_bot', None)
+        up   = self.ev_first - self.ev_min
+        down = self.ev_max   - self.ev_first
+        winning = max(up, down)
+        if winning < a.min_traj:
+            return ('reject_traj', None)
+        timed_out = self.ev_n > a.max_frames
+        if timed_out:
+            is_entry = self.ev_last < self.ev_first
+        else:
+            is_entry = up >= down
+        kind = 'ENTRY' if is_entry else 'EXIT'
+        self.last_fire = self.ix
+        info = dict(kind=kind, first=self.ev_first, min=self.ev_min,
+                    max=self.ev_max, last=self.ev_last, dur=self.ev_n,
+                    up=up, down=down, ix=self.ix)
+        if is_entry: self.entries += 1
+        else:        self.exits   += 1
+        self.fires.append(info)
+        return ('fire', info)
+
+    def step(self, n, miny, maxy, c):
+        self.ix += 1
+        a = self.a
+        refractory = (self.ix - self.last_fire) < a.refractory
+
+        if not self.ev:
+            if not refractory and n >= a.enter_thresh:
+                self.ev = True
+                self.ev_n = 1
+                self.ev_first = self.ev_last = c
+                self.ev_min = c; self.ev_max = c
+                self.ev_miny = miny; self.ev_maxy = maxy
+                self.ev_quiet = 0
+            return None
+
+        self.ev_n += 1
+        if n > 0:
+            self.ev_last = c
+            if c < self.ev_min: self.ev_min = c
+            if c > self.ev_max: self.ev_max = c
+            if miny < self.ev_miny: self.ev_miny = miny
+            if maxy > self.ev_maxy: self.ev_maxy = maxy
+
+        ended = False
+        if n < a.exit_thresh:
+            self.ev_quiet += 1
+            if self.ev_quiet >= a.quiet_frames:
+                ended = True
+                reason = 'quiet'
+        else:
+            self.ev_quiet = 0
+            if self.ev_n > a.max_frames:
+                ended = True
+                reason = 'timeout'
+
+        if ended:
+            result = self._finalize()
+            self._reset()
+            return (reason, result)
+        return None
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument('path', help='log file, or - for stdin')
+    ap.add_argument('--enter',      dest='enter_thresh', type=int,   default=300)
+    ap.add_argument('--exit',       dest='exit_thresh',  type=int,   default=200)
+    ap.add_argument('--quiet',      dest='quiet_frames', type=int,   default=3)
+    ap.add_argument('--min',        dest='min_frames',   type=int,   default=5)
+    ap.add_argument('--max',        dest='max_frames',   type=int,   default=25)
+    ap.add_argument('--extent-top', dest='extent_top',   type=int,   default=10)
+    ap.add_argument('--extent-bot', dest='extent_bot',   type=int,   default=85)
+    ap.add_argument('--min-traj',   dest='min_traj',     type=float, default=15.0)
+    ap.add_argument('--refractory', dest='refractory',   type=int,   default=15)
+    ap.add_argument('--ground-truth', type=int, default=0,
+                    help='Total expected walks for accuracy calc')
+    ap.add_argument('-v', '--verbose', action='store_true',
+                    help='Print every event end, including rejections')
+    args = ap.parse_args()
+
+    text = sys.stdin.read() if args.path == '-' else open(args.path).read()
+
+    det = Detector(args)
+    rejects = {}
+    for n, miny, maxy, c in parse_frames(text):
+        out = det.step(n, miny, maxy, c)
+        if out is None:
+            continue
+        reason, result = out
+        if result is None:
+            continue
+        kind, info = result
+        if kind == 'fire':
+            print(f'  {info["kind"]:5}  first={info["first"]:5.1f}  '
+                  f'min={info["min"]:5.1f}  max={info["max"]:5.1f}  '
+                  f'last={info["last"]:5.1f}  dur={info["dur"]:2d}  '
+                  f'exit={reason}')
+        else:
+            rejects[kind] = rejects.get(kind, 0) + 1
+            if args.verbose:
+                print(f'  [drop {kind}]')
+
+    total = det.entries + det.exits
+    print(f'\n=== entries={det.entries}  exits={det.exits}  total={total} ===')
+    print(f'rejected events: {rejects}')
+    if args.ground_truth:
+        gt = args.ground_truth
+        acc = min(total, gt) / gt * 100
+        over = max(0, total - gt)
+        print(f'accuracy vs gt={gt}: {acc:.0f}% (over={over})')
+
+
+if __name__ == '__main__':
+    main()

tools/serial_monitor.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+# Serial monitor for ESP32. Optionally pulses RTS/DTR to reset the device
+# so we capture boot output. Prefixes each line with elapsed seconds.
+import serial, sys, time, argparse
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--port",    default="/dev/ttyUSB0")
+    ap.add_argument("--baud",    type=int, default=115200)
+    ap.add_argument("--seconds", type=int, default=20)
+    ap.add_argument("--reset",   action="store_true",
+                    help="Pulse RTS/DTR to reset the ESP32 before reading")
+    ap.add_argument("--timestamp", action="store_true",
+                    help="Prefix each line with elapsed seconds since boot")
+    args = ap.parse_args()
+
+    try:
+        s = serial.Serial(args.port, args.baud, timeout=0.2,
+                          rtscts=False, dsrdtr=False)
+    except Exception as e:
+        print(f"[open-fail] {e}", flush=True)
+        sys.exit(2)
+
+    if args.reset:
+        s.setDTR(False)
+        s.setRTS(True)
+        time.sleep(0.1)
+        s.setRTS(False)
+        s.reset_input_buffer()
+
+    t0 = time.time()
+    end = t0 + args.seconds
+    buf = b""
+    while time.time() < end:
+        chunk = s.read(512)
+        if chunk:
+            buf += chunk
+            while b"\n" in buf:
+                line, buf = buf.split(b"\n", 1)
+                text = line.decode("utf-8", errors="replace").rstrip("\r")
+                if args.timestamp:
+                    sys.stdout.write(f"[{time.time()-t0:5.1f}s] {text}\n")
+                else:
+                    sys.stdout.write(text + "\n")
+                sys.stdout.flush()
+    if buf:
+        text = buf.decode("utf-8", errors="replace")
+        if args.timestamp:
+            sys.stdout.write(f"[{time.time()-t0:5.1f}s] {text}\n")
+        else:
+            sys.stdout.write(text)
+        sys.stdout.flush()
+    s.close()
+
+if __name__ == "__main__":
+    main()