Plan: Phase 6 spec + directives round 6 (M18-M24 Friend Tracks, lanes H/J/K)

Markers/badges -> detection -> cross-view triangulation -> track ribbons +
follow-a-friend + LED badge hardware kit. Coordinator-merges policy this phase.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

plan/30-phase6.md

@@ -0,0 +1,214 @@
+# Phase 6 — Friend Tracks (M18–M24): markers → moving people in the 4D scene
+
+Canonical spec for phase 6. **Everything frozen in `../OPUS_BUILD_INSTRUCTIONS.md` (M0–M9)
+and `20-phase5.md` (M10–M17 contracts) still applies.** Standing protocol (status files,
+directives loop, evidence discipline, per-agent worktrees) is unchanged from
+[`README.md`](README.md); the newest round of [`DIRECTIVES.md`](DIRECTIVES.md) always wins.
+
+## The idea
+
+A friend tag today is a *static* anchor. Phase 6 makes friends **move**: wearable markers
+(distinct-hue patches or blinking LED badges) are detected in every camera, associated across
+synced views, triangulated per timestep, and become **tracks** — `t_global → (x,y,z)` paths
+rendered as ribbons in the 3D scene with moving labels, a follow-a-friend camera mode, and
+capsule support. Same machinery as annotation resolution (M8), run automatically over time.
+
+## Context — what exists that you build on (read, don't re-invent)
+
+- `geometry.py` — COLMAP↔Three.js conversion, ray casting, triangulation primitives
+  (`resolve.py` shows exactly how a bbox becomes a 3D point; your solver is that, per-timestep).
+- `frames.py` — frame sampling via ffmpeg (SfM uses it; detection re-uses it).
+- `config.t_video_from_global` / `t_global_from_video` — the FROZEN timebase; detections are
+  found at `t_video`, tracks live at `t_global`.
+- The synthetic fixture (`synthetic.py`) — every acceptance below is against it first.
+- Suite floor is **189 passed**. It only goes up.
+
+## Phase map
+
+```
+Phase 6a (serial, ONE agent)      Phase 6b (parallel, one agent per lane)     Phase 6c (serial)
+┌───────────────────────┐         ┌ lane/h-tracker ─── M19 M20 ──────┐        ┌─────────────────┐
+│ foundation3           │         ├ lane/j-ribbons ─── M21 M22 ──────┤        │ integration3    │
+│ fixture ground truth +│──merge──┤                                  ├──merge─│ full pass +     │
+│ contracts + stubs     │         └ lane/k-badges ──── M23 M24 ──────┘        │ tracked field   │
+│ branch: foundation3   │         (independent — merge in any order)          │ test → v0.3.0   │
+└───────────────────────┘         └──────────────────────────────────         └─────────────────┘
+```
+
+Lanes depend **only** on foundation3, never on each other.
+
+## Milestones
+
+### M18 — foundation3: fixture ground truth, contracts, stubs (serial, ONE agent)
+1. **Synthetic fixture upgrade** (`synthetic.py` — coordinator-sanctioned edit): render **two
+   moving markers** into every camera's video via the existing camera projection:
+   - marker A: a solid bright disc (frozen hue, e.g. pure magenta #ff00ff) following a known
+     smooth trajectory across the stage (e.g. a slow circle, radius ~2, y≈1.5);
+   - marker B: a **blinking** white/bright disc following a different known path, blinking the
+     frozen protocol below with ID=5.
+   Markers must be small (≤2 % of frame area) and rendered *after* the existing content so the
+   full existing suite stays green (offsets, events, poses, SfM tests untouched). Write ground
+   truth to `data/work/track_truth.json`: `{"markers": [{"marker_key": ..., "points":
+   [{"t_global_s", "x", "y", "z"}]}]}` (Three.js scene space).
+2. **DB:** `tracks` + `track_points` tables (contract #2) + `db.py` helpers
+   (`add_track`, `get_tracks`, `set_track_points`, `patch_track`, `delete_track`).
+3. **API:** `GET /api/tracks`, `PATCH /api/tracks/{id}` `{label?, color?}`,
+   `DELETE /api/tracks/{id}`, `POST /api/tracks/solve` (dispatches into the lane-H stub with
+   the house degradation: valid empty result + note while stubbed). Manifest gains
+   `"has_tracks": bool` — update `test_api.py`'s key-set lock consciously in the same commit.
+4. **CLI:** `python -m festival4d track [--detect-only|--solve-only]` → lane-H stubs.
+5. **Backend stubs:** `tracker_detect.py` (`run_detect()`), `tracker_solve.py`
+   (`run_solve()`) — `NotImplementedError` with the full contract in the docstring.
+6. **Frontend:** stub `frontend/src/friendTracks.js` imported from `main.js`, `init()` +
+   per-frame `friendTracks.update(tGlobal)` wired into the master loop (fx.js pattern);
+   hidden **👣 Friends** button `#btn-friends` + empty `#friends-panel` container in
+   `index.html`; `state.tracks = []` loaded at boot when `manifest.has_tracks`.
+7. **Capsule:** add `api/tracks` to `capsule.py`'s bake list (additive; update lane G's
+   bundle-structure test consciously in the same commit, CR-style note in the commit message).
+8. Tests for every new route shape; suite ≥ 189 + new tests. Merge fast — three lanes wait.
+
+### M19 — Marker detection (lane H, backend)
+Fill `tracker_detect.py`. `run_detect()`: sample frames (~8 fps via `frames.py` machinery) from
+every video; detect markers two ways: **color mode** (HSV blob of the frozen marker hues;
+`marker_key = "hue:<bucket>"`) and **blink mode** (per-blob brightness over a sliding window,
+decode the frozen OOK protocol; `marker_key = "code:<id>"`). Write
+`data/work/detections.json` (contract #3). OpenCV (`opencv-python-headless`) is already a
+dependency. No markers → valid-empty detections, never a crash.
+**Accept:** on the synthetic fixture, ≥90 % of sampled frames where a marker is visible yield
+a detection within 3 px (normalized ≤0.008) of the projected ground-truth center; blink ID 5
+decoded; tests in `test_tracker_detect.py`.
+
+### M20 — Track solving (lane H, backend)
+Fill `tracker_solve.py`. `run_solve()`: load detections; group by `marker_key`; per time bucket
+(≈0.25 s) collect same-key detections across cameras at matching `t_global`; **2+ views →
+triangulate** through `geometry` primitives (the `resolve.py` pattern — never inline pose
+math); **1 view → ray ∩ ground plane** (contract #5); smooth each track (moving average or
+Catmull-Rom, your call — document it); write `tracks`/`track_points` through `db` helpers;
+solid color for hue markers, palette color for code markers. `POST /api/tracks/solve` and the
+CLI now run detect→solve end-to-end.
+**Accept:** synthetic recovery — median 3D error of both tracks < 0.3 scene units against
+`track_truth.json`, ≥80 % temporal coverage of each marker's visible span; single-view
+fallback exercised by a test that hides all-but-one camera's detections; degradation (no
+detections → zero tracks + note); tests in `test_tracker_solve.py`.
+
+### M21 — Ribbons, moving labels, friends panel (lane J, frontend)
+Fill `friendTracks.js`. On init (when `manifest.has_tracks`): unhide 👣; fetch
+`/api/tracks` into `state.tracks`. Toggle renders per-track: a **ribbon** polyline through the
+points (track color) + a **moving marker** (sphere + label sprite, position interpolated at
+the current `t_global`, hidden outside the track's time span) — objects via
+`scene3d.addObject/removeObject` only, registered with `scene3d.registerHelper` so photo mode
+hides them. Panel in `#friends-panel` (anchorPanel.js is the style/UX reference — read it,
+don't edit it): list tracks (dot, label, time span), rename/recolor via
+`PATCH /api/tracks/{id}` (controls carry `write-ui`), delete, and a **Follow** button per row.
+**Accept:** live-browser evidence — ribbons + moving labels track the synthetic markers in
+play and scrub; rename/recolor/delete round-trip; photo mode hides ribbons; capsule mode
+hides write controls but keeps ribbons/follow.
+
+### M22 — Follow-a-friend camera (lane J, frontend)
+Chase cam on any track: `scene3d.enterPathMode()` hands you the camera (the camPath.js
+pattern — read it); every `update(tGlobal)` compute the track position, place the camera at a
+smoothed offset (behind/above, ~4 units, low-pass the position so it glides), look at the
+friend (`applyCameraPose`). Esc / Free-roam / snap-to-camera exits (pathMode already handles
+contention — mirror camPath's "someone else took the camera" check).
+**Accept:** live-browser evidence — camera glides after the moving marker in play and scrub;
+clean handoff to/from free-roam, snap-to-cam, and camPath playback; no fighting.
+
+### M23 — LED badge firmware + hardware kit (lane K, hardware/docs)
+`hardware/badge/badge.ino` — ESP32/ATtiny-compatible Arduino sketch blinking the frozen OOK
+protocol (contract #4): configurable 6-bit ID, bright single LED or WS2812; plus
+`hardware/beacon/beacon.ino` — the sync/calibration beacon (distinct reserved ID 63,
+double-brightness). `docs/hardware.md`: parts list (boards, LEDs, battery, diffuser), build
+photos placeholders, wearing guidance (chest/hat height, diffusion, spacing), and the
+camera-side truth: what ranges/framerates the protocol survives (≥24 fps, exposure caveats).
+**Accept:** sketches compile (`arduino-cli compile` for esp32 + attiny if available — else
+document exact compile commands and mark unverified); protocol constants byte-identical to
+contract #4 (import/duplicate them in ONE header with a test-facing copy check documented).
+
+### M24 — Bench self-test tool (lane K, backend script)
+`scripts/badge_selftest.py`: given a short phone clip of a badge on a desk, run the SAME
+decoder path as lane H (`tracker_detect` blink mode) and print the decoded ID + confidence —
+John's hardware smoke test before a shoot. Works on a synthetic self-test too:
+`--synthetic` renders a blinking clip via the fixture helpers and asserts round-trip.
+**Accept:** `uv run python scripts/badge_selftest.py --synthetic` decodes the rendered ID;
+clear failure text for: no blob, ID mismatch, too-short clip. Small test in
+`test_badge_selftest.py` (synthetic path only).
+
+## Contracts (frozen at foundation3 merge)
+
+1. **Marker hues (color mode):** magenta `#ff00ff` and cyan `#00ffff` are the two supported
+   fixture hues; real shoots may configure others via `FESTIVAL4D_MARKER_HUES` (comma-sep hex).
+2. **Schema:**
+   `tracks(id INTEGER PK, marker_key TEXT NOT NULL, label TEXT, color TEXT, created_at TEXT)`
+   `track_points(id INTEGER PK, track_id FK, t_global_s FLOAT, x FLOAT, y FLOAT, z FLOAT,
+   quality FLOAT, views INTEGER)` — points ordered by `t_global_s`; `views` = cameras used
+   (1 = ground-plane fallback); coordinates in **Three.js scene space**.
+   `GET /api/tracks` → `[{id, marker_key, label, color, points: [{t_global_s,x,y,z,quality,views}]}]`.
+3. **detections.json:** `{"videos": {"<video_id>": [{"t_video_s": float, "marker_key": str,
+   "cx": float, "cy": float, "area": float, "conf": float 0..1}]}, "generated_by":
+   "festival4d.tracker_detect"}` — `cx`/`cy` normalized 0..1 (bbox-annotation convention).
+4. **Blink protocol (OOK, camera-decodable):** bit period **133 ms** (4 frames @ 30 fps);
+   word = preamble `11100` + 6-bit ID (MSB first) + even parity = 12 bits, repeated
+   continuously (~1.6 s/word). ID 63 reserved for the sync beacon. Decoder needs ≥24 fps
+   video and ≥1 full word of visibility.
+5. **Ground plane:** the synthetic fixture's ground is `y = 0` (scene space). For real
+   projects the solver estimates it as the 5th-percentile-y horizontal plane of the point
+   cloud and records it in its result dict. Single-view fallback intersects the pixel ray
+   with this plane; such points get `views = 1` and `quality ≤ 0.5`.
+6. **Frozen during 6b:** everything frozen in phases 1–5 **plus** all phase-5 lane modules
+   (`director.js`, `exportVideo.js`, `anchorPanel.js`, `photoMode.js`, `fx.js`,
+   `pathsStore.js`, `audio_features.py`, `director.py`, `capsule.py`) and foundation3's edits
+   (`synthetic.py`, `main.js`, `index.html`, api/cli/db). Lanes fill their own new files only.
+   Believe a frozen file must change → `plan/CHANGE_REQUESTS.md`, work around, integration3
+   adjudicates. Stub-era test assertions superseded by your milestone landing follow the
+   CR-1/-4/-5 pattern: minimal edit + CR entry.
+
+## integration3 scope (Phase 6c)
+Merge order irrelevant; resolve CRs; full synthetic pass (evidence per milestone); raise the
+suite floor; **tracked field test** — real clips with at least one badge/marker in frame
+(combine with the still-open phase-5 field test); failures → `plan/ISSUES.md`; propose
+`v0.3.0` (with `v0.2.0` if the phase-5 field test passes in the same session).
+
+## File ownership (Phase 6b)
+
+| Owner | Files |
+|---|---|
+| Lane H | `backend/festival4d/tracker_detect.py`, `tracker_solve.py`, `backend/tests/test_tracker_detect.py`, `test_tracker_solve.py` |
+| Lane J | `frontend/src/friendTracks.js` |
+| Lane K | `hardware/**`, `docs/hardware.md`, `scripts/badge_selftest.py`, `backend/tests/test_badge_selftest.py` |
+| Every agent | its own `plan/status/<lane>.md` |
+| **Coordinator only** | `plan/DIRECTIVES.md` |
+| **Frozen during 6b** | contract #6 above |
+
+## Phase-6 pitfalls
+
+1. **Time alignment is the whole game.** Detections happen at `t_video`; association happens
+   at `t_global`. One `t_video_from_global` inversion mistake silently shears every track.
+   Use the frozen helpers; test association against ground truth, not against itself.
+2. **Stage lighting lies about color.** The color detector must gate on saturation+value, not
+   hue alone, and the acceptance is on the *synthetic* fixture — note in your status file that
+   real-world hue robustness is a known field-test risk (that's why blink mode exists).
+3. **Blink decoding vs. video fps:** cameras at 24–60 fps sample the 133 ms bit period
+   differently. Decode by integrating brightness per bit window using the video's actual fps
+   (`meta.fps`), never by counting frames.
+4. **Don't fight the camera owners.** Follow-mode (M22) shares `pathMode` with camPath —
+   mirror camPath's contention checks exactly, or two drivers will interleave writes.
+5. **rAF throttle (standing):** verify with the `__f4d` pump in hidden panes
+   (`localStorage f4dDebug=1`); the WebAudio timer exemption gives you ~50 Hz `setTimeout`.
+6. **Fixture compatibility:** foundation3's synthetic edit runs UNDER the existing 189 tests —
+   markers must not move offsets, events, poses, or break SfM-adjacent tests.
+
+## Kickoff prompts (copy-paste one per Opus 4.8 session, in run order)
+
+**foundation3 (first, alone):**
+> Clone ssh://git@100.71.119.27:222/monster/festifun.git. Read OPUS_BUILD_INSTRUCTIONS.md,
+> plan/20-phase5.md, plan/30-phase6.md (M18 is yours), and the latest round of
+> plan/DIRECTIVES.md. Execute foundation3 on branch `foundation3`; maintain
+> plan/status/foundation3.md per plan/status/TEMPLATE.md; suite ≥ 189 + your tests; push the
+> branch and report — the coordinator reviews and merges.
+
+**lane H / lane J / lane K (parallel, after foundation3 merges):**
+> Clone ssh://git@100.71.119.27:222/monster/festifun.git and create your own git worktree
+> before any edit. Read OPUS_BUILD_INSTRUCTIONS.md, plan/30-phase6.md, plan/lane-<X>.md, and
+> the latest round of plan/DIRECTIVES.md. Execute your lane on branch `lane/<x>-<name>`;
+> maintain plan/status/lane-<X>.md; obey the ownership table and frozen-files contract; push
+> your branch and report — the coordinator reviews and merges. Do not merge to main.

plan/DIRECTIVES.md

@@ -4,6 +4,39 @@ Written **only** by the coordinator (the human's planning session). Agents: read
 
 ---
 
+## Round 6 — 2026-07-17 — PHASE 6 planned: Friend Tracks (M18–M24)
+
+**Spec:** `plan/30-phase6.md` (canonical). Lane briefs: `plan/lane-H-tracker.md`,
+`plan/lane-J-ribbons.md`, `plan/lane-K-badges.md`. Kickoff prompts are at the bottom of the
+spec — the human launches each Opus session with one.
+
+**Directives:**
+1. **Now: `foundation3` only** (one agent, branch `foundation3`, M18). Contracts correctness
+   beats speed — three lanes hard-depend on your fixture ground truth, schema, detections
+   shape, and blink protocol. The synthetic-fixture edit must keep all 189 existing tests
+   green (spec pitfall #6). Maintain `plan/status/foundation3.md`. **Push your branch; do NOT
+   merge to main** — this phase the coordinator merges after review (see #4).
+2. **After foundation3 merges — lanes in priority order** (all three concurrently if capacity
+   allows): **H** (tracker — longest, validates every contract), **J** (ribbons/follow — the
+   visible payoff), **K** (badges — independent, hardware-facing). Per-agent worktrees remain
+   MANDATORY.
+3. **Merge policy (changed from Round 4):** agents do NOT merge to main and do NOT tag.
+   Push your lane branch + status file, report completion to the human; the human pings the
+   coordinator session, which reviews (independent suite re-run, ownership check, CR
+   adjudication) and merges in completion order. Everything else from Round 0 protocol
+   (status cadence, blocker rule, evidence discipline) unchanged.
+4. **Review loop:** coordinator reads `plan/status/<lane>.md` + the branch diff on each ping;
+   findings come back as a new DIRECTIVES round or direct merge. Stub-era assertions
+   superseded by a landing milestone: CR entry + minimal edit (CR-1/-4/-5 house pattern).
+5. **integration3** (after all three merge): full synthetic pass, floor raise, tracked field
+   test (fold in the still-open phase-5 field test), `v0.3.0` proposal. `v0.2.0` remains held
+   per Round 5.
+
+**For the human:** (a) launch foundation3 first, alone, with its kickoff prompt; tell the
+coordinator when its status file says ready; (b) then launch H, J, K in parallel; (c) the
+field-test gate is unchanged — real clips in `data/raw/`, now ideally with a marker or badge
+in frame; (d) if you order badge parts, `docs/hardware.md` (lane K) will have the list.
+
 ## Round 5 — 2026-07-17 — PHASE 5 COMPLETE on synthetic; floor 189; v0.2.0 waits on the field test
 
 **Execution report (all same-day):** foundation2 → lanes E/G/F in parallel worktrees (per

plan/README.md

@@ -2,9 +2,12 @@
 
 **Read [`../OPUS_BUILD_INSTRUCTIONS.md`](../OPUS_BUILD_INSTRUCTIONS.md) first — it is the canonical spec** (architecture, repo layout, data model, milestone details M0–M9, pitfalls). This directory only organizes *who builds what, in what order, without colliding*. Lane briefs reference spec milestones by number; they do not restate them.
 
-> **Current phase: 5** (M10–M17) — spec and organization in [`20-phase5.md`](20-phase5.md), lane
-> briefs `lane-E/F/G-*.md`. Phases 1–4 below are complete (v0.1.0 + polish); their protocol
-> sections (git, status, directives loop, evidence discipline) remain the standing rules.
+> **Current phase: 6** (M18–M24, Friend Tracks) — spec and organization in
+> [`30-phase6.md`](30-phase6.md), lane briefs `lane-H/J/K-*.md`, run order in DIRECTIVES
+> Round 6 (note: this phase the **coordinator merges**, agents only push branches).
+> Phases 1–5 below are complete (v0.1.0 shipped; phase 5 M10–M17 accepted on synthetic,
+> suite floor 189, v0.2.0 held for the field test); their protocol sections (git, status,
+> directives loop, evidence discipline) remain the standing rules.
 
 ## Phase map
 

plan/lane-H-tracker.md

@@ -0,0 +1,37 @@
+# Lane H — Tracker (M19 detection, M20 solving)
+
+You turn wearable markers in the videos into 3D friend tracks. Backend only.
+Spec: `30-phase6.md` M19/M20 + contracts #1–#5. Branch `lane/h-tracker`, own worktree.
+
+## What foundation3 gives you
+- Stubs `tracker_detect.py` / `tracker_solve.py` with the contracts in their docstrings;
+  API (`POST /api/tracks/solve` etc.), CLI (`track`), DB helpers, and the synthetic fixture's
+  two moving markers + `data/work/track_truth.json` ground truth — all already wired.
+- You fill the two stub bodies and write the two test files. Nothing else.
+
+## M19 — detection, the parts that bite
+- Sample frames with the `frames.py` machinery (~8 fps is plenty; document your rate).
+- Color mode: convert to HSV, gate on **saturation AND value** before hue (pitfall #2);
+  connected components; centroid → normalized cx/cy. Hue buckets from contract #1 +
+  `FESTIVAL4D_MARKER_HUES`.
+- Blink mode: track candidate bright blobs across the sampled window, integrate brightness
+  per 133 ms bit window **using the video's real fps** (pitfall #3), correlate against the
+  preamble, check parity, emit `code:<id>`.
+- Empty/dark/markerless video → valid-empty detections. Never crash.
+
+## M20 — solving, the parts that bite
+- `t_video → t_global` through the frozen helpers ONLY (pitfall #1).
+- Triangulation through `geometry` primitives exactly as `resolve.py` does — read it first.
+- Bucket ≈0.25 s; 2+ cameras → triangulate (record `views`, `quality` from residual);
+  1 camera → ray ∩ ground plane per contract #5 (`views=1`, `quality ≤ 0.5`).
+- Smooth per track; write through `db` helpers; re-solve replaces that marker's tracks
+  (idempotent — don't stack duplicates on every run).
+
+## Acceptance (evidence in plan/status/lane-H.md)
+- [ ] Detection: ≥90 % recall on visible synthetic markers, ≤0.008 normalized center error;
+      blink ID 5 decoded (`test_tracker_detect.py`)
+- [ ] Solve: median 3D error < 0.3 vs `track_truth.json`, ≥80 % coverage; single-view
+      fallback test; idempotent re-solve; degradations (`test_tracker_solve.py`)
+- [ ] CLI + `POST /api/tracks/solve` run detect→solve end-to-end on the fixture
+- [ ] Suite ≥ foundation3's count + yours, green; stub-era assertions superseded by your
+      landing → CR entry (CR-1/-4/-5 pattern)

plan/lane-J-ribbons.md

@@ -0,0 +1,38 @@
+# Lane J — Ribbons & follow-a-friend (M21, M22)
+
+You make tracks visible and rideable. Pure frontend — ONE file: `frontend/src/friendTracks.js`.
+Spec: `30-phase6.md` M21/M22 + contract #2. Branch `lane/j-ribbons`, own worktree.
+
+## What foundation3 gives you
+- Your stub module imported from main.js with `init()` + per-frame `update(tGlobal)` already
+  called; hidden `#btn-friends` + `#friends-panel` in index.html; `state.tracks` loaded at
+  boot when `manifest.has_tracks`.
+- Read-only building blocks you may CALL but never edit: `scene3d.addObject/removeObject`,
+  `registerHelper` (photo mode hides you for free), `enterPathMode`/`exitPathMode`/
+  `applyCameraPose` (the camPath.js pattern — read that file first), `focusOn`;
+  `PATCH/DELETE /api/tracks/{id}`. anchorPanel.js is your UX/style reference (inject your own
+  <style> tag; reuse the CSS vars). Mark mutating controls `write-ui`.
+
+## M21 — ribbons + panel, the parts that bite
+- Interpolate the moving marker between track points at the current tGlobal (linear is fine);
+  HIDE it outside the track's span — don't park it at the ends.
+- Rebuild ribbons only on tracks-changed, not per frame; per-frame work = one position lerp
+  per visible track (fx.js shows the hot-path discipline).
+- Empty tracks (solver not run) → panel says so, no errors; capsule mode: ribbons + follow
+  stay, write controls hidden.
+
+## M22 — follow cam, the parts that bite
+- Mirror camPath's contention handling EXACTLY: if `scene3d.pathMode` goes false under you
+  (snap-to-cam, Esc, free-roam), stop following without a fight (pitfall #4).
+- Low-pass the camera position (e.g. lerp factor ~0.08/frame) so it glides; look at the
+  friend, offset ~4 units behind/above; scrubbing far must not whiplash (clamp the lerp on
+  big jumps: teleport if the target moved > ~5 units).
+- Starting a camPath playback or clicking 🎬 must cleanly cancel follow mode (and vice versa).
+
+## Acceptance (evidence in plan/status/lane-J.md — you likely can't drive a browser;
+write defensively, list exactly what the coordinator must verify live)
+- [ ] Ribbons + moving labels track the synthetic markers in play AND scrub
+- [ ] Panel: rename/recolor (PATCH) + delete round-trip; `write-ui` on mutators
+- [ ] Follow glides after a friend; clean handoffs with free-roam / snap / camPath / 🎬
+- [ ] Photo mode hides ribbons (registerHelper); capsule keeps read-only features
+- [ ] `npm run build` clean; backend suite unchanged and green

plan/lane-K-badges.md

@@ -0,0 +1,40 @@
+# Lane K — LED badges & bench kit (M23 firmware+docs, M24 self-test)
+
+You build the wearable side: badge firmware speaking the frozen blink protocol, the hardware
+guide, and the bench self-test John runs before a shoot. Spec: `30-phase6.md` M23/M24 +
+contract #4. Branch `lane/k-badges`, own worktree.
+
+## M23 — firmware + docs, the parts that bite
+- Contract #4 is FROZEN: 133 ms bit, `11100` preamble + 6-bit ID + even parity, continuous
+  repeat, ID 63 = sync beacon. Keep the constants in ONE header (`hardware/badge/protocol.h`)
+  shared by badge.ino and beacon.ino; document the manual-sync rule with
+  `tracker_detect.py`'s decoder constants (can't import across languages — state both
+  locations in the header comment and in docs/hardware.md).
+- badge.ino: plain Arduino APIs (millis()-paced, no delay()-drift), single bright LED on a
+  PWM pin OR a WS2812 (compile-time #define), ID set by #define (document per-badge flashing).
+  Hardware is never ideal on paper: expose a `BIT_TRIM_US` calibration knob for clock drift.
+- beacon.ino: ID 63, double LED brightness/size guidance.
+- docs/hardware.md: parts list with rough prices (ESP32 dev board / ATtiny85, LED + resistor
+  or WS2812, LiPo/coin cell, diffuser ping-pong ball), wiring, flashing (`arduino-cli`
+  commands), wearing guidance (chest/hat, diffusion, one badge per person, ≥24 fps cameras,
+  exposure caveat: blown-out video kills OOK contrast).
+- Compile check: `arduino-cli compile --fqbn esp32:esp32:esp32` (and attiny if the core is
+  installable). If arduino-cli isn't available in your environment, document the exact
+  commands and mark the box unverified — do NOT claim compiled without output.
+
+## M24 — bench self-test, the parts that bite
+- `scripts/badge_selftest.py` must run lane H's REAL decoder (`tracker_detect` blink path) —
+  import it, don't re-implement; if lane H hasn't merged yet, code against the frozen
+  contract #3/#4 shapes and mark the integration box pending (integration3 re-runs it).
+- `--synthetic` mode: render a small blinking clip using the fixture's marker-rendering
+  helpers (foundation3 exposes them in synthetic.py) and assert the ID round-trips.
+- Clear, John-readable failure messages: no blob found / decoded wrong ID / clip too short
+  (< 1 word). Exit codes: 0 ok, 1 decode-fail, 2 usage.
+
+## Acceptance (evidence in plan/status/lane-K.md)
+- [ ] protocol.h constants byte-identical to contract #4; badge + beacon sketches compile
+      (output pasted) or compile commands documented + marked unverified
+- [ ] docs/hardware.md complete enough that John can order parts from it
+- [ ] `uv run python scripts/badge_selftest.py --synthetic` decodes the rendered ID
+      (`test_badge_selftest.py` covers it); failure paths print actionable text
+- [ ] Backend suite green; `npm` untouched