feat(feedback): add a /feedback command recorded through the command plane

Register a global `/feedback` command so a user can record a remark about the
session without spending a model turn. `/feedback <text>` acknowledges; empty
or whitespace-only input returns a usage error.

The plugin appends no session event of its own. `dsh-commands` already writes
a `command/run` / `command/done` pair for every dispatched command, carrying
the verbatim text and the settled outcome, and both records are log-only and
non-surface. The feedback is therefore durably in the session log and invisible
to the model without this package touching the log format.

Text is never parsed, so `/feedback /plan felt slow` records that literal
content. Nothing consumes the records; capture is deliberately inert.

New group `packages/feedback/` — no existing group owns feedback capture. Its
row raises the packages/README.md word ceiling by 10, which had no headroom;
one redundant sentence there was removed to offset most of the cost.

packages/feedback/command-feedback/src/index.ts

@@ -0,0 +1,40 @@
+/**
+ * Human-facing `/feedback` command. It records a remark about the session and
+ * does nothing else: the command registry's own `command/run` and
+ * `command/done` events are the whole record, so this plugin only validates the
+ * input and acknowledges it. Those appends are eager but unflushed, so the
+ * acknowledgement reports the entry is logged, not that it reached disk.
+ * @module @deepseek-ai/dsh-command-feedback
+ */
+
+import type { Context } from 'cordis'
+import type { CommandInvocation, CommandResult } from '@deepseek-ai/dsh-commands'
+
+export const name = 'command-feedback'
+export const inject = ['commands']
+
+const USAGE = 'Usage: /feedback <text>'
+
+/**
+ * Validate and acknowledge one feedback entry. `command/run` already carries
+ * the verbatim text, so no further append is needed; returning an error instead
+ * settles that record as `kind: 'error'` and leaves no accepted feedback.
+ * @param invocation - receiving agent, raw command input, and UI cancellation.
+ * @returns an acknowledgement, or a usage error when no feedback text was supplied.
+ */
+function executeFeedbackCommand(invocation: CommandInvocation): CommandResult {
+  if (invocation.rawInput.trim().length === 0) {
+    return { kind: 'error', text: `Feedback text is required. ${USAGE}` }
+  }
+  return { kind: 'success', text: 'Feedback recorded.' }
+}
+
+/** Register the global `/feedback` command for every composed command adapter. */
+export function apply(ctx: Context): void {
+  ctx.commands.register({
+    name: 'feedback',
+    description: 'record feedback about this session',
+    input: { hint: '<text>' },
+    handler: executeFeedbackCommand,
+  })
+}