diff --git a/apps/opencode-plugin/index.ts b/apps/opencode-plugin/index.ts
index 74fb02bcc..4b36abaca 100644
--- a/apps/opencode-plugin/index.ts
+++ b/apps/opencode-plugin/index.ts
@@ -16,7 +16,8 @@
  */
 
 import { type Plugin, tool } from "@opencode-ai/plugin";
-import { existsSync, mkdirSync, readFileSync, writeFileSync } from "fs";
+import { existsSync, mkdirSync, readFileSync, unlinkSync, writeFileSync } from "fs";
+import { homedir } from "os";
 import path from "path";
 
 // OpenCode's @hono/node-server patches global.Response with a polyfill that
@@ -67,6 +68,7 @@ import { composeImproveContext } from "@plannotator/shared/pfm-reminder";
 import {
   stripConflictingPlanModeRules,
 } from "./plan-mode";
+import { sanitizeTag } from "@plannotator/shared/project";
 import {
   applyWorkflowConfig,
   isPlanningAgent,
@@ -127,12 +129,13 @@ interface PlanEdit {
 }
 
 /**
- * Backing file for the current plan. Managed entirely by the plugin;
+ * Backing file for the current plan. Stored outside the workspace in
+ * `~/.plannotator/active/{project}/_active-plan.md` so it never appears
+ * in git status or editor file trees. Managed entirely by the plugin;
  * the agent never sees or touches this file directly.
  */
-export function getPlanBackingPath(directory: string): string {
-  const planDir = path.join(directory, ".opencode", "plans");
-  return path.join(planDir, "_active-plan.md");
+export function getPlanBackingPath(project: string): string {
+  return path.join(homedir(), ".plannotator", "active", project, "_active-plan.md");
 }
 
 /**
@@ -560,7 +563,8 @@ Use /plannotator-last or /plannotator-annotate for manual review, or set workflo
           }
 
           // Read existing backing file (empty on first call)
-          const backingPath = getPlanBackingPath(ctx.directory);
+          const project = sanitizeTag(path.basename(ctx.directory)) || "_unknown";
+          const backingPath = getPlanBackingPath(project);
           const backingDir = path.dirname(backingPath);
           mkdirSync(backingDir, { recursive: true });
 
@@ -636,6 +640,9 @@ Use /plannotator-last or /plannotator-annotate for manual review, or set workflo
           server.stop();
 
           if (result.approved) {
+            // Clean up backing file after approval
+            try { unlinkSync(backingPath); } catch { /* already gone */ }
+
             const shouldSwitchAgent = result.agentSwitch && result.agentSwitch !== 'disabled';
             const targetAgent = result.agentSwitch || 'build';
 
diff --git a/apps/opencode-plugin/submit-plan.test.ts b/apps/opencode-plugin/submit-plan.test.ts
index e0eb32e2c..8280d15c2 100644
--- a/apps/opencode-plugin/submit-plan.test.ts
+++ b/apps/opencode-plugin/submit-plan.test.ts
@@ -1,4 +1,6 @@
 import { describe, expect, test } from "bun:test";
+import { homedir } from "os";
+import path from "path";
 import {
   applyEdits,
   formatWithLineNumbers,
@@ -162,14 +164,14 @@ describe("formatWithLineNumbers", () => {
 // ── getPlanBackingPath ─────────────────────────────────────────────────────
 
 describe("getPlanBackingPath", () => {
-  test("returns path inside .opencode/plans within the given directory", () => {
-    const result = getPlanBackingPath("/some/project");
-    expect(result).toBe("/some/project/.opencode/plans/_active-plan.md");
+  test("returns path inside ~/.plannotator/active/{project}/_active-plan.md", () => {
+    const result = getPlanBackingPath("myproject");
+    expect(result).toBe(path.join(homedir(), ".plannotator", "active", "myproject", "_active-plan.md"));
   });
 
-  test("uses the provided directory as the root", () => {
-    const result = getPlanBackingPath("/home/user/myproject");
-    expect(result).toContain("/home/user/myproject");
+  test("uses the provided project name as the directory segment", () => {
+    const result = getPlanBackingPath("some-project");
+    expect(result).toContain(path.join(".plannotator", "active", "some-project"));
     expect(result).toContain("_active-plan.md");
   });
 });