feat(feedback): disclose session sharing in the /feedback acknowledgement

The /feedback acknowledgement now echoes the receiving session id and
reports the mounted telemetry backend's sharing policy: the telemetry seam
exposes a backend-independent TelemetrySharingStatus through a required
abstract sharing member on the Telemetry service, the OTel backend maps its
mode onto it, and the command appends one policy-only sharing sentence
(full / feedback-only / disabled / not configured) to the acknowledgement.
The web client renders the text through the existing command row without a
client change; a new assembled-browser e2e mounts the shipped telemetry row
in FULL mode against a local dead endpoint and pins the shipped default
sentence as a keyless golden.

packages/session/session-telemetry/src/index.ts

@@ -130,6 +130,15 @@ export interface TelemetryBackend {
   shutdown(): Promise<void>
 }
 
+/**
+ * Deployment-selected session-sharing policy disclosed by a mounted
+ * {@link Telemetry} backend to human-facing acknowledgement surfaces (the
+ * `/feedback` command's confirmation text). The seam owns the vocabulary so
+ * any backend can disclose a policy without depending on the OTel package;
+ * the values mirror the OTel backend's serialized `TelemetryMode` choices.
+ */
+export type TelemetrySharingStatus = 'full' | 'feedback-only' | 'disabled'
+
 /**
  * Loadable form of the backend contract: one implementation per context —
  * the cordis `Service` registration under the `telemetry` key throws on a
@@ -141,6 +150,15 @@ export abstract class Telemetry extends Service implements TelemetryBackend {
     super(ctx, 'telemetry')
   }
 
+  /**
+   * Deployment-selected session-sharing policy, disclosed for acknowledgement
+   * surfaces that report whether recorded feedback leaves the process. Every
+   * backend must disclose its policy; a consumer renders "not configured" only
+   * when no telemetry service is mounted. The seam owns this vocabulary so the
+   * disclosure is backend-independent.
+   */
+  abstract readonly sharing: TelemetrySharingStatus
+
   /**
    * See {@link TelemetryBackend.emit} — that declaration is the contract's one home.
    * @param record - the logical record to report; owned by the backend after the call.