diff --git a/packages/core/src/core/__snapshots__/prompts.test.ts.snap b/packages/core/src/core/__snapshots__/prompts.test.ts.snap
index b58dc8ce40..d4cbb26dfd 100644
--- a/packages/core/src/core/__snapshots__/prompts.test.ts.snap
+++ b/packages/core/src/core/__snapshots__/prompts.test.ts.snap
@@ -176,7 +176,8 @@ The following read-only tools are available in Plan Mode:
 - \`write_file\` - Save plans to the plans directory (see Plan Storage below)
 
 ## Plan Storage
-- Save your plans as Markdown (.md) files directly to: \`/tmp/project-temp/plans/\`
+- Save your plans as Markdown (.md) files ONLY within: \`/tmp/project-temp/plans/\`
+- You are restricted to writing files within this directory while in Plan Mode.
 - Use descriptive filenames: \`feature-name.md\` or \`bugfix-description.md\`
 
 ## Workflow Phases
diff --git a/packages/core/src/prompts/snippets.ts b/packages/core/src/prompts/snippets.ts
index 7070c8189d..c41934760c 100644
--- a/packages/core/src/prompts/snippets.ts
+++ b/packages/core/src/prompts/snippets.ts
@@ -305,7 +305,8 @@ ${options.planModeToolsList}
 - \`${WRITE_FILE_TOOL_NAME}\` - Save plans to the plans directory (see Plan Storage below)
 
 ## Plan Storage
-- Save your plans as Markdown (.md) files directly to: \`${options.plansDir}/\`
+- Save your plans as Markdown (.md) files ONLY within: \`${options.plansDir}/\`
+- You are restricted to writing files within this directory while in Plan Mode.
 - Use descriptive filenames: \`feature-name.md\` or \`bugfix-description.md\`
 
 ## Workflow Phases
diff --git a/packages/core/src/tools/exit-plan-mode.ts b/packages/core/src/tools/exit-plan-mode.ts
index d96eb00600..08fa97601c 100644
--- a/packages/core/src/tools/exit-plan-mode.ts
+++ b/packages/core/src/tools/exit-plan-mode.ts
@@ -53,6 +53,7 @@ export class ExitPlanModeTool extends BaseDeclarativeTool<
     private config: Config,
     messageBus: MessageBus,
   ) {
+    const plansDir = config.storage.getProjectTempPlansDir();
     super(
       EXIT_PLAN_MODE_TOOL_NAME,
       'Exit Plan Mode',
@@ -64,8 +65,7 @@ export class ExitPlanModeTool extends BaseDeclarativeTool<
         properties: {
           plan_path: {
             type: 'string',
-            description:
-              'The file path to the finalized plan (e.g., "plans/feature-x.md").',
+            description: `The file path to the finalized plan (e.g., "${plansDir}/feature-x.md"). This path MUST be within the designated plans directory: ${plansDir}/`,
           },
         },
       },