diff --git a/package-lock.json b/package-lock.json
index 617ffb8..ba8a2d7 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2715,7 +2715,7 @@
     },
     "plugins/thread-badges": {
       "name": "bb-plugin-thread-badges",
-      "version": "0.1.0",
+      "version": "0.2.0",
       "license": "MIT",
       "dependencies": {
         "@hugeicons/core-free-icons": "^4.1.3",
diff --git a/plugins/workflow-stages/PLUGIN_OVERVIEW.md b/plugins/workflow-stages/PLUGIN_OVERVIEW.md
index 994bb07..8215f4a 100644
--- a/plugins/workflow-stages/PLUGIN_OVERVIEW.md
+++ b/plugins/workflow-stages/PLUGIN_OVERVIEW.md
@@ -25,6 +25,13 @@ turn needs you. Every automatic move skips sticky stages, and "work stops" only
 undoes the move "a turn starts" made, so a thread you filed by hand while it was
 running stays filed.
 
+One automatic move ships on: a message that asks for a plan files its thread
+under Planning. Filing is otherwise the agent's job, and plan mode is the one
+moment an agent may not do it — `bb stages set` is a mutating call, and plan
+mode forbids those — so without this a `/plan` thread sits unfiled for the whole
+planning session. It reads the composer's own command mention rather than the
+message text, so a thread that merely discusses `/plan` is not filed.
+
 ## How it works
 
 Ribbon owns the sidebar — rendering, drag-and-drop, manual order, and the stored
diff --git a/plugins/workflow-stages/README.md b/plugins/workflow-stages/README.md
index eb0e05a..ab5083f 100644
--- a/plugins/workflow-stages/README.md
+++ b/plugins/workflow-stages/README.md
@@ -70,6 +70,7 @@ Configured in the same editor:
 | Trigger | Default |
 | --- | --- |
 | A thread with no placement | Inbox |
+| A message asks for a plan | Planning |
 | A turn starts | off |
 | Work stops | off |
 | A question, an approval, or a failed turn | off |
@@ -77,6 +78,19 @@ Configured in the same editor:
 "Work stops" only undoes the move "a turn starts" made, so a thread you filed by
 hand while it was running stays filed. Every automatic move skips sticky stages.
 
+"A message asks for a plan" is the one that ships **on**, because it is the one
+trigger the agent cannot answer for itself. Filing is otherwise the agent's job:
+it reads the stage table below and runs `bb stages set`. In plan mode it may not
+— that is a mutating shell call, and plan mode is the one moment an agent is not
+allowed to make those — so a thread you started with `/plan` would sit in Inbox
+through the whole planning session and only get filed once the plan was
+approved, by which point the honest stage is Building.
+
+Detection is the composer's, not a string match: bb's plan action is a
+provider-declared slash command, and the send carries it as a structured mention
+rather than as text. So a message that merely *talks* about `/plan` is not one,
+and a provider that calls its plan action something else is still recognised.
+
 The last one ships off on purpose. A stage says where the work is; whether it
 needs you is a different axis, and Ribbon already draws that on the row itself.
 Pointing it at a stage means a thread bounces there every time an agent asks a
diff --git a/plugins/workflow-stages/app.tsx b/plugins/workflow-stages/app.tsx
index 087aaf8..fd94b0b 100644
--- a/plugins/workflow-stages/app.tsx
+++ b/plugins/workflow-stages/app.tsx
@@ -447,6 +447,15 @@ function WorkflowSettings() {
             {options(false)}
           </select>
         </Row>
+        <Row label="When a plan is asked for">
+          <select
+            className={cn(FIELD, "max-w-64")}
+            value={state.config.planStageId ?? ""}
+            onChange={(event) => configure({ planStageId: event.target.value || null })}
+          >
+            {options(true)}
+          </select>
+        </Row>
         <Row label="When a turn starts">
           <select
             className={cn(FIELD, "max-w-64")}
@@ -475,9 +484,11 @@ function WorkflowSettings() {
           </select>
         </Row>
         <p className="text-sm text-subtle-foreground">
-          A question, an approval, or a failed turn counts as needing you. Automatic moves skip
-          any stage marked <em>only the user files here</em>, and "when work stops" only undoes
-          the move "when a turn starts" made.
+          A plan is asked for when a message opens with your provider's plan command, which is
+          the one trigger the agent cannot answer itself. A question, an approval, or a failed
+          turn counts as needing you. Automatic moves skip any stage marked{" "}
+          <em>only the user files here</em>, and "when work stops" only undoes the move "when a
+          turn starts" made.
         </p>
       </div>
     </div>
diff --git a/plugins/workflow-stages/server.ts b/plugins/workflow-stages/server.ts
index 04c254c..2388b3e 100644
--- a/plugins/workflow-stages/server.ts
+++ b/plugins/workflow-stages/server.ts
@@ -9,7 +9,11 @@
 // plugin — `getGroupingCatalogV1` — plus the placement calls in ribbon.ts.
 // Nothing has to be registered with Ribbon, and nothing here replaces bb's
 // sidebar.
-import { defineRpcContract, type BbPluginApi } from "@get-bb/plugin-sdk";
+import {
+  defineRpcContract,
+  type BbPluginApi,
+  type PluginDispatchInput,
+} from "@get-bb/plugin-sdk";
 import { z } from "zod";
 import { GLYPHS, GLYPH_NAMES, GROUPING_GLYPH } from "./icons";
 import {
@@ -179,6 +183,15 @@ export default async function plugin(bb: BbPluginApi) {
       const suffix = marks.length === 0 ? "" : ` (${marks.join(", ")})`;
       lines.push(`- ${stage.id} — ${stage.label}${suffix}: ${stage.description || "No rule set."}`);
     }
+    const planStage = config.planStageId === null ? null : store.get(config.planStageId);
+    if (planStage !== null) {
+      lines.push(
+        "",
+        `A message that asks for a plan files the thread under ${planStage.label} on its own,`,
+        "before you read this. Rule 1 is already satisfied there — leave it, and move it on",
+        "when the plan is agreed and you start building.",
+      );
+    }
     lines.push(
       "",
       "A stage marked user-only is the user's call: never file into or out of one —",
@@ -269,6 +282,90 @@ export default async function plugin(bb: BbPluginApi) {
     }
   }
 
+  // ------------------------------------------------------------- plan mode
+
+  // Nothing on a thread says "this one is planning": no event carries it, and
+  // `ThreadResponse` has no field for it. The message does. bb's plan composer
+  // action is a provider-declared slash command, so a plan-mode send arrives
+  // as a text block whose leading mention is that command — which is why this
+  // hangs off the dispatch hook rather than off `bb.events`.
+  //
+  // The agent cannot file itself here even though the instructions ask it to:
+  // `bb stages set` is a mutating shell call, and plan mode is the one moment
+  // an agent is not allowed to make those. So the plugin does it instead.
+  const FALLBACK_PLAN_COMMANDS: ReadonlySet<string> = new Set(["plan"]);
+  let planCommands: ReadonlySet<string> = FALLBACK_PLAN_COMMANDS;
+  let planCommandsReadAt = 0;
+  /** Long enough that installing a provider mid-session is picked up. */
+  const PLAN_COMMAND_TTL_MS = 5 * 60 * 1000;
+
+  /**
+   * Ask each provider what it calls its plan action, so this recognises a
+   * provider that named it something other than "plan". Never awaited from the
+   * hook: the dispatch pass holds a server-wide lock, so it reads whatever the
+   * last refresh left and the first send of a session runs on the fallback.
+   */
+  async function refreshPlanCommands(): Promise<void> {
+    planCommandsReadAt = Date.now();
+    try {
+      const names = new Set(FALLBACK_PLAN_COMMANDS);
+      for (const provider of await bb.sdk.providers.list()) {
+        for (const action of provider.composerActions) {
+          if (action.kind === "plan") names.add(action.command.name);
+        }
+      }
+      planCommands = names;
+    } catch (cause) {
+      // Bind-gated before the server is listening, and a provider list is not
+      // worth failing a send over. The fallback still names Claude Code's.
+      bb.log.debug(
+        `plan command refresh skipped: ${cause instanceof Error ? cause.message : String(cause)}`,
+      );
+    }
+  }
+
+  /**
+   * A plan send, told from an ordinary one. The mention must open the message —
+   * the composer prepends the command — and be a command rather than a skill,
+   * so a skill that happens to be called "plan" does not file the thread.
+   */
+  function isPlanDispatch(input: PluginDispatchInput): boolean {
+    return input.blocks.some(
+      (block) =>
+        block.type === "text" &&
+        block.mentions.some(
+          (mention) =>
+            mention.start === 0 &&
+            mention.resource.kind === "command" &&
+            mention.resource.source === "command" &&
+            planCommands.has(mention.resource.name),
+        ),
+    );
+  }
+
+  bb.experimental_hooks.on("message.dispatch", (context) => {
+    // Fail-closed, time-boxed, and holding a lock every other send queues
+    // behind: decide synchronously, never throw, and let the move happen off
+    // the pass. The answer is always the same one — this hook watches, it does
+    // not gate. Re-running on a drain or a retry is harmless because moving a
+    // thread to the stage it is already in is a no-op.
+    try {
+      if (isPlanDispatch(context.input)) {
+        void automaticMove(context.thread.id, store.config().planStageId);
+      }
+      if (Date.now() - planCommandsReadAt > PLAN_COMMAND_TTL_MS) {
+        void refreshPlanCommands();
+      }
+    } catch (cause) {
+      bb.log.debug(
+        `plan filing skipped: ${cause instanceof Error ? cause.message : String(cause)}`,
+      );
+    }
+    return { action: "proceed" };
+  });
+
+  // ------------------------------------------------------------ transitions
+
   bb.events.on("thread.active", ({ thread }) => {
     void automaticMove(thread.id, store.config().activeStageId);
   });
diff --git a/plugins/workflow-stages/skills/workflow-stages/SKILL.md b/plugins/workflow-stages/skills/workflow-stages/SKILL.md
index 2c3bb7c..1fe28c8 100644
--- a/plugins/workflow-stages/skills/workflow-stages/SKILL.md
+++ b/plugins/workflow-stages/skills/workflow-stages/SKILL.md
@@ -38,6 +38,12 @@ yet, so the evidence rule below would say "wait" — and a whole planning sessio
 would pass with the thread sitting where nobody can see it was picked up. Decide
 from what you are about to do, not from what has happened.
 
+The exception is plan mode, which files itself. A message sent with the plan
+command moves its thread to the planning stage before you read anything, because
+you could not do it yourself there — `bb stages set` mutates, and plan mode
+forbids that. So in a plan-mode turn the first move is already made: leave it,
+and move the thread on when the plan is agreed and you start building.
+
 If no stage describes what you are about to do — a question, a code read, a
 chore that fits none of them — leave the thread in the default stage. That
 escape is for no stage fitting. It is not for being unsure which of two fits:
diff --git a/plugins/workflow-stages/stages.ts b/plugins/workflow-stages/stages.ts
index b2c9637..c91adc2 100644
--- a/plugins/workflow-stages/stages.ts
+++ b/plugins/workflow-stages/stages.ts
@@ -38,6 +38,8 @@ export const configSchema = z
     idleStageId: z.string().nullable(),
     /** Entered when the agent asks a question or a turn fails. */
     attentionStageId: z.string().nullable(),
+    /** Entered when a message asks the provider for a plan. */
+    planStageId: z.string().nullable(),
   })
   .strict();
 export type WorkflowConfig = z.output<typeof configSchema>;
@@ -122,11 +124,18 @@ const SEED: ReadonlyArray<SeedStage> = [
 // already draws per row. Filing a question-asking thread back to the default
 // stage would undo the first move on every clarification, so the attention
 // bounce ships off and stays a setting for anyone who wants that queue.
+//
+// Plan mode is the exception that ships on. The other three read a thread's
+// runtime — busy, idle, waiting — and guess a workflow position from it, which
+// is why they are off by default. Asking for a plan is not a guess: the user
+// said what the next stretch of work is, and Planning is the stage that says
+// it back.
 const DEFAULT_CONFIG: WorkflowConfig = {
   defaultStageId: "inbox",
   activeStageId: null,
   idleStageId: null,
   attentionStageId: null,
+  planStageId: "planning",
 };
 
 /** A stored icon is only as trustworthy as whatever wrote it. */
@@ -218,6 +227,7 @@ export function createStageStore(database: BetterSqlite3.Database): StageStore {
       activeStageId: resolve("activeStageId", DEFAULT_CONFIG.activeStageId),
       idleStageId: resolve("idleStageId", DEFAULT_CONFIG.idleStageId),
       attentionStageId: resolve("attentionStageId", DEFAULT_CONFIG.attentionStageId),
+      planStageId: resolve("planStageId", DEFAULT_CONFIG.planStageId),
     };
   }
   function writeConfig(patch: Partial<WorkflowConfig>): WorkflowConfig {