diff --git a/bin/gstack-repo-mode b/bin/gstack-repo-mode
index 0b4d6da64..0aabe378e 100755
--- a/bin/gstack-repo-mode
+++ b/bin/gstack-repo-mode
@@ -12,13 +12,20 @@
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-# Compute SLUG directly (avoid eval of gstack-slug — branch names can contain shell metacharacters)
+# Keep the no-remote early exit before consulting gstack-slug. gstack-slug falls
+# back to the directory basename when origin is missing, which would incorrectly
+# make local-only repos eligible for classification.
 REMOTE_URL=$(git remote get-url origin 2>/dev/null || true)
 if [ -z "$REMOTE_URL" ]; then
   echo "REPO_MODE=unknown"
   exit 0
 fi
-SLUG=$(echo "$REMOTE_URL" | sed 's|.*[:/]\([^/]*/[^/]*\)\.git$|\1|;s|.*[:/]\([^/]*/[^/]*\)$|\1|' | tr '/' '-')
+# Consume the canonical cached slug from gstack-slug (sed, never eval — branch
+# names can contain shell metacharacters). Invoke from the git root so the
+# PWD-keyed slug cache matches other gstack project-state writers.
+REPO_ROOT=$(git rev-parse --show-toplevel 2>/dev/null || true)
+[ -z "${REPO_ROOT:-}" ] && { echo "REPO_MODE=unknown"; exit 0; }
+SLUG=$(cd "$REPO_ROOT" && "$SCRIPT_DIR/gstack-slug" | sed -n 's/^SLUG=//p' | head -1)
 [ -z "${SLUG:-}" ] && { echo "REPO_MODE=unknown"; exit 0; }
 
 # Validate: only allow known values (prevent shell injection via source <(...))
diff --git a/test/gstack-repo-mode.test.ts b/test/gstack-repo-mode.test.ts
new file mode 100644
index 000000000..62088a217
--- /dev/null
+++ b/test/gstack-repo-mode.test.ts
@@ -0,0 +1,176 @@
+/**
+ * Project-slug consistency for gstack-repo-mode.
+ *
+ * These are end-to-end reproductions of #2212. Each case is a real local Git
+ * workspace which predates its public GitHub origin: gstack-slug caches the
+ * local directory name, then the origin is added. repo-mode must write its
+ * cache next to that canonical project state, not beside a newly derived
+ * owner-repo slug.
+ */
+
+import { describe, expect, test } from 'bun:test';
+import { spawnSync } from 'child_process';
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const REPO_MODE_BIN = path.join(ROOT, 'bin', 'gstack-repo-mode');
+const SLUG_BIN = path.join(ROOT, 'bin', 'gstack-slug');
+
+type CommandResult = { stdout: string; stderr: string; status: number };
+
+function run(command: string, args: string[], cwd: string, home: string): CommandResult {
+  const result = spawnSync(command, args, {
+    cwd,
+    encoding: 'utf8',
+    env: { ...process.env, HOME: home, GSTACK_HOME: path.join(home, '.gstack') },
+  });
+  return {
+    stdout: result.stdout ?? '',
+    stderr: result.stderr ?? '',
+    status: result.status ?? -1,
+  };
+}
+
+function git(args: string[], cwd: string, home: string) {
+  const result = run('git', args, cwd, home);
+  expect(result.status, `${result.stderr}\n${result.stdout}`).toBe(0);
+}
+
+function slugFrom(output: string): string {
+  const line = output.split('\n').find((entry) => entry.startsWith('SLUG='));
+  expect(line).toBeDefined();
+  return line!.slice('SLUG='.length);
+}
+
+const publicWorkspaces = [
+  { name: 'react-local-history', origin: 'https://github.com/facebook/react.git' },
+  { name: 'next-local-history', origin: 'https://github.com/vercel/next.js.git' },
+  { name: 'kubernetes-local-history', origin: 'https://github.com/kubernetes/kubernetes.git' },
+];
+
+describe('gstack-repo-mode cached slug consistency (#2212)', () => {
+  for (const workspace of publicWorkspaces) {
+    test(`${workspace.origin} keeps its pre-origin project cache`, () => {
+      const home = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-home-'));
+      const root = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-workspaces-'));
+      const project = path.join(root, workspace.name);
+
+      try {
+        fs.mkdirSync(project);
+        git(['init', '-b', 'main'], project, home);
+        git(['config', 'user.name', 'gstack regression test'], project, home);
+        git(['config', 'user.email', 'test@gstack.dev'], project, home);
+
+        // This workspace existed and used gstack before it adopted GitHub.
+        const initialSlug = slugFrom(run(SLUG_BIN, [], project, home).stdout);
+        expect(initialSlug).toBe(workspace.name);
+
+        // Five commits make repo-mode perform its real classification path.
+        for (let commit = 1; commit <= 5; commit += 1) {
+          fs.writeFileSync(path.join(project, `commit-${commit}.txt`), String(commit));
+          git(['add', '.'], project, home);
+          git(['commit', '-m', `commit ${commit}`], project, home);
+        }
+        git(['remote', 'add', 'origin', workspace.origin], project, home);
+
+        const mode = run(REPO_MODE_BIN, [], project, home);
+        expect(mode.status, mode.stderr).toBe(0);
+        expect(mode.stdout.trim()).toBe('REPO_MODE=solo');
+
+        // Canonical slug stays the pre-origin basename; remote-derived twin must not appear.
+        const projectsDir = path.join(home, '.gstack', 'projects');
+        const canonicalCache = path.join(projectsDir, initialSlug, 'repo-mode.json');
+        expect(fs.existsSync(canonicalCache)).toBe(true);
+        expect(fs.readdirSync(projectsDir)).toEqual([initialSlug]);
+
+        // Slug remains sanitized even when the remote URL would otherwise diverge.
+        expect(initialSlug).toMatch(/^[a-zA-Z0-9._-]+$/);
+        expect(slugFrom(run(SLUG_BIN, [], project, home).stdout)).toBe(initialSlug);
+      } finally {
+        fs.rmSync(home, { recursive: true, force: true });
+        fs.rmSync(root, { recursive: true, force: true });
+      }
+    });
+  }
+
+  test('still treats a workspace without origin as unknown', () => {
+    const home = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-home-'));
+    const project = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-local-only-'));
+    try {
+      git(['init', '-b', 'main'], project, home);
+      const mode = run(REPO_MODE_BIN, [], project, home);
+      expect(mode.status, mode.stderr).toBe(0);
+      expect(mode.stdout.trim()).toBe('REPO_MODE=unknown');
+      expect(fs.existsSync(path.join(home, '.gstack', 'projects'))).toBe(false);
+    } finally {
+      fs.rmSync(home, { recursive: true, force: true });
+      fs.rmSync(project, { recursive: true, force: true });
+    }
+  });
+
+  test('subdir invocation still writes under the git-root cached slug', () => {
+    const home = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-home-'));
+    const root = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-subdir-'));
+    const project = path.join(root, 'nested-history');
+    const nested = path.join(project, 'packages', 'app');
+    try {
+      fs.mkdirSync(nested, { recursive: true });
+      git(['init', '-b', 'main'], project, home);
+      git(['config', 'user.name', 'gstack regression test'], project, home);
+      git(['config', 'user.email', 'test@gstack.dev'], project, home);
+
+      const initialSlug = slugFrom(run(SLUG_BIN, [], project, home).stdout);
+      expect(initialSlug).toBe('nested-history');
+
+      for (let commit = 1; commit <= 5; commit += 1) {
+        fs.writeFileSync(path.join(project, `commit-${commit}.txt`), String(commit));
+        git(['add', '.'], project, home);
+        git(['commit', '-m', `commit ${commit}`], project, home);
+      }
+      git(['remote', 'add', 'origin', 'https://github.com/facebook/react.git'], project, home);
+
+      const mode = run(REPO_MODE_BIN, [], nested, home);
+      expect(mode.status, mode.stderr).toBe(0);
+      expect(mode.stdout.trim()).toBe('REPO_MODE=solo');
+
+      const projectsDir = path.join(home, '.gstack', 'projects');
+      expect(fs.existsSync(path.join(projectsDir, initialSlug, 'repo-mode.json'))).toBe(true);
+      expect(fs.readdirSync(projectsDir)).toEqual([initialSlug]);
+    } finally {
+      fs.rmSync(home, { recursive: true, force: true });
+      fs.rmSync(root, { recursive: true, force: true });
+    }
+  });
+
+  test('sanitizes unusual origin URLs via gstack-slug before mkdir', () => {
+    const home = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-home-'));
+    const project = fs.mkdtempSync(path.join(os.tmpdir(), 'grepo-weird-url-'));
+    try {
+      git(['init', '-b', 'main'], project, home);
+      git(['config', 'user.name', 'gstack regression test'], project, home);
+      git(['config', 'user.email', 'test@gstack.dev'], project, home);
+
+      for (let commit = 1; commit <= 5; commit += 1) {
+        fs.writeFileSync(path.join(project, `commit-${commit}.txt`), String(commit));
+        git(['add', '.'], project, home);
+        git(['commit', '-m', `commit ${commit}`], project, home);
+      }
+      // Free-form remote URL with characters outside [a-zA-Z0-9._-]
+      git(['remote', 'add', 'origin', 'https://example.com/org/my repo (v2).git'], project, home);
+
+      const mode = run(REPO_MODE_BIN, [], project, home);
+      expect(mode.status, mode.stderr).toBe(0);
+      expect(mode.stdout.trim()).toBe('REPO_MODE=solo');
+
+      const projects = fs.readdirSync(path.join(home, '.gstack', 'projects'));
+      expect(projects).toHaveLength(1);
+      expect(projects[0]).toMatch(/^[a-zA-Z0-9._-]+$/);
+      expect(projects[0]).not.toMatch(/[ ()]/);
+    } finally {
+      fs.rmSync(home, { recursive: true, force: true });
+      fs.rmSync(project, { recursive: true, force: true });
+    }
+  });
+});