diff --git a/plugins/provider-claude-code/src/bridge/__tests__/bridge.test.ts b/plugins/provider-claude-code/src/bridge/__tests__/bridge.test.ts
index 1517ecd67..0e61ba669 100644
--- a/plugins/provider-claude-code/src/bridge/__tests__/bridge.test.ts
+++ b/plugins/provider-claude-code/src/bridge/__tests__/bridge.test.ts
@@ -1887,6 +1887,82 @@ describe("bridge", () => {
     }
   });
 
+  // Regression for #1712: `/plan` sent on a LATER turn of a live session. The
+  // server puts `claudeCodePermissionMode: "plan"` in providerOptions on
+  // turn/start, but the bridge only ever applied the permission mode at
+  // session construction. The mention was stripped from the prompt and the
+  // prompt was pushed into a session still in the user's preset mode, so
+  // Claude never entered Plan mode and never called ExitPlanMode.
+  it("switches a live session into Plan mode when a later turn carries /plan", async () => {
+    const bridge = createBridgeJsonRpcTestHarness(handleLine);
+    const queries: ControlledClaudeQuery[] = [];
+    queryMock.mockImplementation(() => {
+      const query = createControlledClaudeQuery();
+      queries.push(query);
+      return query;
+    });
+
+    try {
+      const threadId = "thread-plan-mid-conversation";
+      // Turn 1: a normal accept-edits session (no plan mode).
+      await startBridgeThread({ bridge, threadId });
+      const query = queries[0];
+      const call = getLatestQueryCall();
+      if (!query) {
+        throw new Error("Expected live Claude query");
+      }
+      expect(call.options.permissionMode).toBe("acceptEdits");
+
+      // Turn 2: the user types "/plan ..." into the existing thread. The
+      // server strips nothing; it forwards the mention plus the plan knob.
+      bridge.sendRequest(
+        2,
+        "turn/start",
+        canonicalTurnParams({
+          threadId,
+          input: [
+            {
+              type: "text",
+              text: "/plan Create hello.txt containing hello world",
+              mentions: [
+                {
+                  start: 0,
+                  end: 5,
+                  resource: {
+                    kind: "command",
+                    trigger: "/",
+                    name: "plan",
+                    source: "command",
+                    origin: "builtin",
+                    label: "plan",
+                    argumentHint: null,
+                  },
+                },
+              ],
+            },
+          ],
+          providerOptions: { claudeCodePermissionMode: "plan" },
+        }),
+      );
+      await bridge.waitForResponse(2);
+      const prompt = await readNextPromptText(call);
+
+      // The `/plan` token is stripped (correct: the CLI would treat it as a
+      // second command) ...
+      expect(prompt).toBe("Create hello.txt containing hello world");
+      // ... so the ONLY thing that can put the session into Plan mode is the
+      // live permission-mode switch. On the base commit this is never called.
+      expect(query.setPermissionMode).toHaveBeenCalledWith("plan");
+      // No session rebuild either — the same query stays live.
+      expect(queries).toHaveLength(1);
+      expect(query.close).not.toHaveBeenCalled();
+
+      await stopBridgeThread({ bridge, queries, threadId });
+    } finally {
+      bridge.restore();
+    }
+  });
+
   it("denies ExitPlanMode without prompting when the plan is missing", async () => {
     const bridge = createBridgeJsonRpcTestHarness(handleLine);
     const queries: ControlledClaudeQuery[] = [];
diff --git a/plugins/provider-claude-code/src/bridge/bridge.ts b/plugins/provider-claude-code/src/bridge/bridge.ts
index efdd25192..2bbb6a4dd 100644
--- a/plugins/provider-claude-code/src/bridge/bridge.ts
+++ b/plugins/provider-claude-code/src/bridge/bridge.ts
@@ -1701,6 +1701,29 @@ function createForwardUserQuestionRequest(
     });
 }
 
+/**
+ * `/plan` on a later turn of a live session. Session construction used to be
+ * the only place the permission mode was applied, so a mid-conversation
+ * `/plan` stripped the mention and pushed the prompt into a session that was
+ * still in the user's preset mode: no plan-mode reminder, no ExitPlanMode
+ * proposal. Switch the live SDK session into Plan mode before the prompt is
+ * pushed; the preset stays in `approvedPlanPermissionMode` for the approval
+ * to restore.
+ */
+async function enterPlanModeIfRequested(
+  threadSession: ThreadSession,
+  params: TurnStartParams | TurnSteerParams,
+): Promise<void> {
+  if (
+    params.claudeCodePermissionMode !== "plan" ||
+    threadSession.permissionMode === "plan"
+  ) {
+    return;
+  }
+  threadSession.permissionMode = "plan";
+  await threadSession.session.setPermissionMode("plan");
+}
+
 /**
  * Leave Plan mode once the user approves a plan.
  *
@@ -2281,6 +2304,7 @@ async function runTurnStart(
       params.threadId,
       withTurnLiveSessionSettings(threadSession.liveSettings, params),
     );
+    await enterPlanModeIfRequested(threadSession, params);
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error);
     sendError(id, -32000, message);
@@ -2346,6 +2370,7 @@ async function runTurnSteer(
       params.threadId,
       withTurnLiveSessionSettings(threadSession.liveSettings, params),
     );
+    await enterPlanModeIfRequested(threadSession, params);
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error);
     sendError(id, -32000, message);
diff --git a/plugins/provider-claude-code/src/bridge/commands.ts b/plugins/provider-claude-code/src/bridge/commands.ts
index 4b9874c44..5e6efeab4 100644
--- a/plugins/provider-claude-code/src/bridge/commands.ts
+++ b/plugins/provider-claude-code/src/bridge/commands.ts
@@ -94,6 +94,9 @@ export const claudeTurnStartParamsSchema = z.object({
   providerSubagentsEnabled: z.boolean().optional(),
   config: z.record(z.string(), z.unknown()).optional(),
   permissionEscalation: bridgePermissionEscalationSchema,
+  // `/plan` on a later turn: the live session must switch into Plan mode
+  // before the prompt is pushed. Undefined keeps the session's current mode.
+  claudeCodePermissionMode: z.literal("plan").optional(),
 });
 
 export const claudeTurnSteerParamsSchema = z.object({
@@ -107,6 +110,7 @@ export const claudeTurnSteerParamsSchema = z.object({
   memoryEnabled: z.boolean().optional(),
   providerSubagentsEnabled: z.boolean().optional(),
   permissionEscalation: bridgePermissionEscalationSchema,
+  claudeCodePermissionMode: z.literal("plan").optional(),
 });
 
 /** The canonical Provider Bridge Protocol params, per method. */
diff --git a/plugins/provider-claude-code/src/session-params.ts b/plugins/provider-claude-code/src/session-params.ts
index 97f935904..d781e63aa 100644
--- a/plugins/provider-claude-code/src/session-params.ts
+++ b/plugins/provider-claude-code/src/session-params.ts
@@ -328,5 +328,8 @@ export function buildClaudeTurnParams(
     memoryEnabled: providerOptions.memoryEnabled,
     providerSubagentsEnabled: providerOptions.providerSubagentsEnabled,
     permissionEscalation: args.options.permissionEscalation,
+    ...(providerOptions.claudeCodePermissionMode !== undefined
+      ? { claudeCodePermissionMode: providerOptions.claudeCodePermissionMode }
+      : {}),
   };
 }