feat(05-03): freeze guidance_sessions envelope as types-only contract (GREEN)

- GuidanceSessionEnvelope: EXACTLY id, chat_id, route_snapshot, created_at
  (SessionClaim field-freeze law — a 5th property means drift)
- GuidanceRouteSnapshot INLINE (D-07: one key, one TTL, ~2h): destination
  id/name, distanceM/durationS, polyline6 geometry (05-01 storage format),
  startedAtSec resume anchor
- GUIDANCE_SESSION_TTL_SECONDS = 7200 — every Phase 6 write carries it
- guidance:<id> key-scheme doc header; zero runtime behavior (no binding,
  no function, no import — GE4 pins it)

Note: header says 'No KV binding' rather than naming the KV type because
the acceptance gate requires that token to appear NOWHERE in the file,
comments included — same law, gate-clean wording.

bot/src/kv/guidance-sessions.ts

@@ -0,0 +1,58 @@
+/*
+ * guidance-sessions.ts — the FROZEN Phase 6 contract, types-only (D-06/D-07).
+ * ------------------------------------------------------------------------
+ * THIS MODULE SHIPS NO BEHAVIOR. No KV binding, no Env field, no wrangler
+ * namespace, no runtime function — the envelope is designed here (ROADMAP
+ * §Phase 5 GUID-05/06 upstream obligation) so Phase 6 builds its service
+ * on a frozen shape. Phase 6's service owns every write; every write
+ * carries expirationTtl: GUIDANCE_SESSION_TTL_SECONDS (~2h) and the
+ * snapshot is INLINE (one key, one TTL) — nothing outlives 2h, nothing is
+ * reconstructable after expiry (D-07, the location-pin TTL precedent).
+ *
+ * Key scheme: guidance:<id> → JSON GuidanceSessionEnvelope
+ */
+
+/** ~2h (D-06) — the envelope's every future write carries THIS value as its
+ *  expirationTtl (Phase 6's privacy grep gate extends the TTL-law to it). */
+export const GUIDANCE_SESSION_TTL_SECONDS = 7200;
+
+/**
+ * The route snapshot — INLINE in the envelope (D-07): one KV key, one TTL.
+ * Nothing outlives 2h; nothing is reconstructable after expiry. Scoped to
+ * what a chat turn-card needs (GUID-05): the selected route's headline data
+ * + its geometry for the map snapshot render + the trip-start anchor for
+ * progress math on resume (GUID-06).
+ */
+export interface GuidanceRouteSnapshot {
+  /** The gazetteer id of the trip's destination. */
+  destinationId: string;
+  /** The destination's display name (verbatim gazetteer name). */
+  destinationName: string;
+  /** Selected route summary (meters / seconds). */
+  distanceM: number;
+  durationS: number;
+  /** The SELECTED route's geometry, polyline6-encoded — the routing
+   *  workspace's storage format (05-01), never a re-serialized array. */
+  geometry: string;
+  /** Trip start, seconds-since-epoch — the resume-progress anchor (GUID-06). */
+  startedAtSec: number;
+}
+
+/**
+ * The guidance_sessions envelope — Phase 6's frozen contract (D-06).
+ * EXACTLY these four fields: a 5th property means drift (the SessionClaim
+ * law, bot/src/kv/sessions.ts).
+ *
+ * Key scheme: guidance:<id>  → JSON GuidanceSessionEnvelope
+ * Every write MUST carry expirationTtl: GUIDANCE_SESSION_TTL_SECONDS.
+ */
+export interface GuidanceSessionEnvelope {
+  /** Opaque session id — crypto.randomUUID() at Phase 6 mint (T-02-05 precedent). */
+  id: string;
+  /** The Telegram chat the turn-cards push to (GUID-05). */
+  chat_id: number;
+  /** The INLINE route snapshot (D-07) — never a reference or a second key. */
+  route_snapshot: GuidanceRouteSnapshot;
+  /** Envelope creation, seconds-since-epoch. */
+  created_at: number;
+}