diff --git a/.changeset/git-boundary.md b/.changeset/git-boundary.md
new file mode 100644
index 0000000..62ecf17
--- /dev/null
+++ b/.changeset/git-boundary.md
@@ -0,0 +1,10 @@
+---
+"@united-workforce/cli": patch
+---
+
+fix: stop parent traversal at .git boundary
+
+`findWorkflowInParents()` and `discoverProjectWorkflows()` now stop traversing
+parent directories when they encounter a `.git` directory or file (git worktree).
+This prevents picking up unrelated `.workflow/` directories above the repository
+root in monorepo setups.
diff --git a/packages/cli/src/__tests__/workflow-list-recursive.test.ts b/packages/cli/src/__tests__/workflow-list-recursive.test.ts
index 6421906..c328e95 100644
--- a/packages/cli/src/__tests__/workflow-list-recursive.test.ts
+++ b/packages/cli/src/__tests__/workflow-list-recursive.test.ts
@@ -183,6 +183,122 @@ describe("discoverProjectWorkflows — parent traversal", () => {
   });
 });
 
+// ── discoverProjectWorkflows — .git boundary ─────────────────────────────────
+
+describe("discoverProjectWorkflows — .git boundary", () => {
+  test("G1: .git directory stops traversal", async () => {
+    // Setup: tmpDir/repo/.git/ (dir), tmpDir/.workflow/leak.yaml, start from tmpDir/repo/sub/deep/
+    const repoDir = join(tmpDir, "repo");
+    const gitDir = join(repoDir, ".git");
+    await mkdir(gitDir, { recursive: true });
+
+    // Workflow above repo root — should NOT be reachable
+    const leakDir = join(tmpDir, ".workflow");
+    await mkdir(leakDir, { recursive: true });
+    await writeFile(join(leakDir, "leak.yaml"), await createWorkflowYaml("leak"));
+
+    const startFrom = join(repoDir, "sub", "deep");
+    await mkdir(startFrom, { recursive: true });
+
+    const entries = await discoverProjectWorkflows(startFrom);
+    expect(entries).toEqual([]);
+  });
+
+  test("G2: .git file (worktree) stops traversal", async () => {
+    // Setup: tmpDir/repo/.git as a FILE, tmpDir/.workflow/leak.yaml, start from tmpDir/repo/pkg/
+    const repoDir = join(tmpDir, "repo");
+    await mkdir(repoDir, { recursive: true });
+    await writeFile(join(repoDir, ".git"), "gitdir: /some/other/path/.git/worktrees/repo");
+
+    const leakDir = join(tmpDir, ".workflow");
+    await mkdir(leakDir, { recursive: true });
+    await writeFile(join(leakDir, "leak.yaml"), await createWorkflowYaml("leak"));
+
+    const startFrom = join(repoDir, "pkg");
+    await mkdir(startFrom, { recursive: true });
+
+    const entries = await discoverProjectWorkflows(startFrom);
+    expect(entries).toEqual([]);
+  });
+
+  test("G3: workflow at .git boundary IS found", async () => {
+    // Setup: tmpDir/repo/.git/ (dir), tmpDir/repo/.workflow/local.yaml, start from tmpDir/repo/sub/
+    const repoDir = join(tmpDir, "repo");
+    const gitDir = join(repoDir, ".git");
+    await mkdir(gitDir, { recursive: true });
+
+    const wfDir = join(repoDir, ".workflow");
+    await mkdir(wfDir, { recursive: true });
+    await writeFile(join(wfDir, "local.yaml"), await createWorkflowYaml("local"));
+
+    const startFrom = join(repoDir, "sub");
+    await mkdir(startFrom, { recursive: true });
+
+    const entries = await discoverProjectWorkflows(startFrom);
+    expect(entries.map((e) => e.name)).toContain("local");
+  });
+
+  test("G4: workflow below .git is found, above is not", async () => {
+    // Setup: tmpDir/repo/.git/ + tmpDir/repo/.workflow/local.yaml + tmpDir/.workflow/leak.yaml
+    const repoDir = join(tmpDir, "repo");
+    const gitDir = join(repoDir, ".git");
+    await mkdir(gitDir, { recursive: true });
+
+    const localWfDir = join(repoDir, ".workflow");
+    await mkdir(localWfDir, { recursive: true });
+    await writeFile(join(localWfDir, "local.yaml"), await createWorkflowYaml("local"));
+
+    const leakDir = join(tmpDir, ".workflow");
+    await mkdir(leakDir, { recursive: true });
+    await writeFile(join(leakDir, "leak.yaml"), await createWorkflowYaml("leak"));
+
+    const startFrom = join(repoDir, "sub");
+    await mkdir(startFrom, { recursive: true });
+
+    const entries = await discoverProjectWorkflows(startFrom);
+    expect(entries.map((e) => e.name)).toEqual(["local"]);
+  });
+});
+
+// ── findWorkflowInParents (via cmdThreadStart) — .git boundary ───────────────
+
+describe("findWorkflowInParents via cmdThreadStart — .git boundary", () => {
+  test("G5: .git stops traversal — workflow above boundary is not found", async () => {
+    await makeUwfStore(storageRoot);
+    const repoDir = join(tmpDir, "repo");
+    const gitDir = join(repoDir, ".git");
+    await mkdir(gitDir, { recursive: true });
+
+    // Workflow above .git boundary
+    const leakDir = join(tmpDir, ".workflow");
+    await mkdir(leakDir, { recursive: true });
+    await writeFile(join(leakDir, "leak.yaml"), await createWorkflowYaml("leak"));
+
+    const startFrom = join(repoDir, "sub");
+    await mkdir(startFrom, { recursive: true });
+
+    // cmdThreadStart should fail — "leak" is above the .git boundary
+    await expect(cmdThreadStart(storageRoot, "leak", "prompt", startFrom)).rejects.toThrow();
+  });
+
+  test("G6: workflow at .git boundary IS found via cmdThreadStart", async () => {
+    await makeUwfStore(storageRoot);
+    const repoDir = join(tmpDir, "repo");
+    const gitDir = join(repoDir, ".git");
+    await mkdir(gitDir, { recursive: true });
+
+    const wfDir = join(repoDir, ".workflow");
+    await mkdir(wfDir, { recursive: true });
+    await writeFile(join(wfDir, "local.yaml"), await createWorkflowYaml("local"));
+
+    const startFrom = join(repoDir, "sub");
+    await mkdir(startFrom, { recursive: true });
+
+    const result = await cmdThreadStart(storageRoot, "local", "prompt", startFrom);
+    expect(result.workflow).toMatch(/^[0-9A-HJKMNP-TV-Z]{13}$/);
+  });
+});
+
 // ── cmdWorkflowList — parent traversal ───────────────────────────────────────
 
 describe("cmdWorkflowList — parent traversal", () => {
diff --git a/packages/cli/src/commands/thread.ts b/packages/cli/src/commands/thread.ts
index 4676cd8..bc19f76 100644
--- a/packages/cli/src/commands/thread.ts
+++ b/packages/cli/src/commands/thread.ts
@@ -1,6 +1,6 @@
 import { execFileSync, spawn } from "node:child_process";
 import { access, readFile } from "node:fs/promises";
-import { dirname, isAbsolute, resolve as resolvePath } from "node:path";
+import { dirname, isAbsolute, join, resolve as resolvePath } from "node:path";
 import type { VarStore } from "@ocas/core";
 import { validate } from "@ocas/core";
 import type {
@@ -287,6 +287,16 @@ async function findWorkflowInDir(dir: string, name: string): Promise<string | nu
   return null;
 }
 
+/** Check if a directory contains a .git marker (directory or file). */
+async function hasGitMarker(dir: string): Promise<boolean> {
+  try {
+    await access(join(dir, ".git"));
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 /**
  * Traverse parent directories looking for `.workflow/<name>.yaml` or `.workflow/<name>.yml`.
  * Returns the absolute path if found, otherwise null.
@@ -302,6 +312,11 @@ async function findWorkflowInParents(startDir: string, name: string): Promise<st
       return found;
     }
 
+    // Stop at .git boundary (repo root)
+    if (await hasGitMarker(currentDir)) {
+      break;
+    }
+
     // Stop at filesystem root
     if (currentDir === root) {
       break;
diff --git a/packages/cli/src/store.ts b/packages/cli/src/store.ts
index c2d6dab..a3b6b56 100644
--- a/packages/cli/src/store.ts
+++ b/packages/cli/src/store.ts
@@ -82,6 +82,31 @@ async function scanWorkflowDir(dir: string): Promise<ProjectWorkflowEntry[]> {
   return result;
 }
 
+/** Merge primary (.workflow/) and legacy (.workflows/) entries, primary wins on name collision. */
+function mergeWorkflowEntries(
+  primary: ProjectWorkflowEntry[],
+  legacy: ProjectWorkflowEntry[],
+): ProjectWorkflowEntry[] {
+  const seen = new Set(primary.map((e) => e.name));
+  const merged = [...primary];
+  for (const entry of legacy) {
+    if (!seen.has(entry.name)) {
+      merged.push(entry);
+    }
+  }
+  return merged;
+}
+
+/** Check if a directory contains a .git marker (directory or file). */
+async function hasGitMarker(dir: string): Promise<boolean> {
+  try {
+    await access(join(dir, ".git"));
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 /**
  * Discover project-local workflows by walking from `startDir` up through parent
  * directories. The nearest directory that contains a `.workflow/` or `.workflows/`
@@ -96,8 +121,9 @@ async function scanWorkflowDir(dir: string): Promise<ProjectWorkflowEntry[]> {
  * `uwf thread start`, so `uwf workflow list` and `uwf thread start` agree on
  * what's discoverable from any given subdirectory.
  *
- * Returns an empty array if no `.workflow/` or `.workflows/` directory exists
- * anywhere from `startDir` up to the filesystem root.
+ * Traversal stops at the first `.git` boundary (directory or file) or the
+ * filesystem root. Returns an empty array if no `.workflow/` or `.workflows/`
+ * directory exists within that range.
  */
 export async function discoverProjectWorkflows(startDir: string): Promise<ProjectWorkflowEntry[]> {
   let currentDir = resolvePath(startDir);
@@ -108,14 +134,12 @@ export async function discoverProjectWorkflows(startDir: string): Promise<Projec
     const legacy = await scanWorkflowDir(join(currentDir, ".workflows"));
 
     if (primary.length > 0 || legacy.length > 0) {
-      const seen = new Set(primary.map((e) => e.name));
-      const merged = [...primary];
-      for (const entry of legacy) {
-        if (!seen.has(entry.name)) {
-          merged.push(entry);
-        }
-      }
-      return merged;
+      return mergeWorkflowEntries(primary, legacy);
+    }
+
+    // Stop at .git boundary (repo root)
+    if (await hasGitMarker(currentDir)) {
+      return [];
     }
 
     // Stop at filesystem root