feat(06-06): the D-10 locked-follow guidance camera + the context-aware BackButton resolver (GREEN)

- guidance/camera.ts: GUIDANCE_CAMERA_PADDING {320,64,64,64} / ZOOM 16 /
  EASE_MS 400 / PITCH 35; easeToSnapped rides the follow controller (ONE
  easing discipline) and never passes bearing — north-up, recorded call;
  onRerouteApplied is the documented camera no-op (setData lives in the
  route layer)
- map/follow.ts: follow(point, opts?) pose overrides spread over the
  Phase 3/5 defaults — no-opts calls stay byte-identical (RS13); the
  re-lock announces the mode (the recenter notch's return signal, RS12);
  the originalEvent unlock law untouched
- telegram/backbutton.ts: BackAction resolver ({hidden|close|callback})
  consulted per click + wire.sync() visibility re-apply (visible iff
  actionable); the legacy (hasOverlay, walkBack) shape composes internally
  so Phase 5 call sites and RS7 stay valid; close() only at the true root

web/src/guidance/camera.ts

@@ -0,0 +1,79 @@
+/*
+ * camera.ts — the D-10 locked-follow guidance camera.
+ * -----------------------------------------------------------------------------
+ * Guidance's camera rides the SNAPPED line (one authority — D-05): every
+ * accepted fix eases to the puck's foot on the route, never the raw GPS
+ * fix. The pose is the UI-SPEC camera table, pinned here as named
+ * constants (RS11 asserts the values):
+ *
+ *   padding {top 320, bottom 64, left 64, right 64} — map-space px;
+ *     T − B = 256 ≈ 0.30 × 844 reference viewport → center ≈65% down-screen
+ *   pitch 35 — the standing pitch; guidance never changes it (D-10)
+ *   zoom 16  — GUIDANCE_ZOOM, urban detail (replay-tunable)
+ *   400 ms   — GUIDANCE_EASE_MS, the RECENTER_DURATION_MS easing family
+ *
+ * BEARING IS NEVER PASSED — north-up is a recorded call (UI-SPEC §Camera
+ * Behavior): the heading cone already communicates direction and a rotating
+ * map contradicts the calm-instrument posture. RS11 pins the absence of the
+ * bearing key on every ease.
+ *
+ * The ease rides the Phase 3 follow controller (ONE easing discipline, ONE
+ * unlock law): follow.ts's originalEvent rule is the whole mechanism — a
+ * programmatic ease never reads as the user panning; a user gesture unlocks
+ * and the recenter control's notch clears (RS12). onRerouteApplied is a
+ * DOCUMENTED camera no-op: the rerouted line snaps in via setData in the
+ * route layer and the next per-fix ease settles the viewport — no camera
+ * jump (UI-SPEC camera table, "Reroute snaps in" row).
+ *
+ * Node-testable: maplibre appears only as erased types; the ease is a call
+ * on the injected follow controller (the route-surface fakeMap pattern).
+ */
+import type { Map as MapLibreMap } from "maplibre-gl";
+import type { RoutePoint } from "@araharah/routing/src/index.ts";
+import type { FollowOptions } from "../map/follow.ts";
+
+/** The UI-SPEC guidance padding — center ≈65% down-screen (D-10). */
+export const GUIDANCE_CAMERA_PADDING: NonNullable<FollowOptions["padding"]> = {
+  top: 320,
+  bottom: 64,
+  left: 64,
+  right: 64,
+};
+/** Urban-detail zoom (the UI-SPEC camera table's GUIDANCE_ZOOM). */
+export const GUIDANCE_ZOOM = 16;
+/** The one easing discipline — 400 ms (the follow.ts family). */
+export const GUIDANCE_EASE_MS = 400;
+/** The standing pitch — guidance never changes it (D-10). */
+export const GUIDANCE_CAMERA_PITCH = 35;
+
+export interface GuidanceCamera {
+  /** Ease to the SNAPPED foot on the route line at the guidance pose. */
+  easeToSnapped(point: RoutePoint): void;
+  /** The reroute snap-in: a documented camera no-op — the new line's setData
+   *  happens in the route layer; the next per-fix ease settles the viewport. */
+  onRerouteApplied(): void;
+}
+
+/** The pose's executor is the follow controller (one easing discipline; the
+ *  `map` parameter names the viewport the pose applies to and keeps the
+ *  constructor symmetric with createFollowController). */
+export function createGuidanceCamera(
+  map: MapLibreMap | null,
+  followController: { follow(point: { lat: number; lng: number }, opts?: FollowOptions): void },
+): GuidanceCamera {
+  return {
+    easeToSnapped(point: RoutePoint): void {
+      followController.follow(point, {
+        padding: GUIDANCE_CAMERA_PADDING,
+        pitch: GUIDANCE_CAMERA_PITCH,
+        zoom: GUIDANCE_ZOOM,
+        durationMs: GUIDANCE_EASE_MS,
+      });
+    },
+    onRerouteApplied(): void {
+      // camera no-op by contract — RS11 pins zero moves (map motion settles
+      // naturally on the next per-fix ease; UI-SPEC "Reroute snaps in").
+      void map;
+    },
+  };
+}