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/README.md

@@ -8,6 +8,12 @@ The telemetry Service Definition declares the `TelemetryBackend` contract, and i
 
 `TelemetryBackend` has three members: `emit(record)` MUST enqueue without blocking because it runs synchronously during `session/event` or explicit canonical-log replay; optional `flush()` is a fire-and-forget hint after a turn ends, and most backends omit it and use their SDK's normal batching schedule; `shutdown()` drains queued records and resolves when the SDK stops, and disposal awaits it. An implementation that provides `flush()` must order concurrent flushes with the final `shutdown()` drain. `Telemetry` registers this API under the `telemetry` context key; each context accepts one implementation, and a duplicate load throws. A backend constructs `TelemetryCoordinator` with `live` or `on-demand` capture and calls `captureSession(session, throughSeq?)` at its chosen trigger.
 
+The service also carries the required [`TelemetrySharingStatus`](#the-sharing-disclosure) `sharing` member: the deployment-selected sharing policy every backend must disclose to human-facing acknowledgement surfaces (the `/feedback` command's confirmation). A consumer renders "not configured" only when no telemetry service is mounted. The seam owns the vocabulary (`full` | `feedback-only` | `disabled`) so any backend can disclose a policy without depending on the OTel package.
+
+## The sharing disclosure
+
+The acknowledgement of a recorded feedback entry reports whether and how the session is shared, read from the mounted backend's `sharing`. A backend sets the property from its deployment configuration: `full` (every event is handed over as it happens), `feedback-only` (nothing is handed over until a `feedback/record` event releases the unreleased prefix through it), or `disabled` (nothing is handed over at all). Consumers map the status onto user-facing copy; the disclosure never claims delivery — handoff is the non-blocking enqueue, and batching, retry, and loss policy stay the backend SDK's.
+
 ## Capture points
 
 In `live` mode the coordinator registers, all through the composing fiber's effects: `session/created` (adopt: record the header, read the log back through the projection from the construction boundary — constructor seeds from fork/resume never re-emit on the firehose and never re-export), `session/event` (project, deep-copy, redact, then hand off; zero I/O), `session/flush` (forward the optional `flush()` hint and return void — the loop's awaited parallel must never wait on telemetry), `session/disposed` (capture the session's `shutdown` operational record at its termination edge, then retire it), `agent/error` (the one live-bus relay; the session event vocabulary intentionally has no operational-error record), a dispose effect (capture shutdown for each still-live session, then await the backend's `shutdown()`; failures warn instead of throwing), and an adoption sweep of `ctx.sessions.list()` (a hot reload does not replay `session/created`). In `on-demand` mode it registers only the dispose effect: `captureSession()` reads the canonical log through an optional inclusive sequence boundary, while flush hints and operational events remain local.