diff --git a/skills/stack/SKILL.md b/skills/stack/SKILL.md
index f9359ac..f8e7770 100644
--- a/skills/stack/SKILL.md
+++ b/skills/stack/SKILL.md
@@ -193,6 +193,12 @@ Mutating merge workflows stream progress while they run. Expect live progress fo
 retargeting, backup, merge/auto-merge, waiting, and cleanup before the final
 summary.
 
+Worktree cleanup has two separate cases. Descendant branches checked out in
+clean sibling worktrees can be repaired from their owning worktree; dirty owners
+fail before mutation. After a root lands, if the landed branch is checked out in
+a clean sibling worktree, Stack detaches that worktree at `HEAD` before deleting
+the local branch; a dirty owner fails before the hosted merge starts.
+
 ## Understand Or Undo The Last Mutation
 
 ```bash
diff --git a/src/services/Git.ts b/src/services/Git.ts
index e3ee984..68a545a 100644
--- a/src/services/Git.ts
+++ b/src/services/Git.ts
@@ -45,6 +45,7 @@ export interface Interface {
     parent: string,
     commits: ReadonlyArray<string>,
   ) => Effect.Effect<void, ExecError>;
+  readonly release: (branch: string) => Effect.Effect<void, ExecError>;
   readonly backup: (branch: string, name: string) => Effect.Effect<void, ExecError>;
   readonly drop: (branch: string) => Effect.Effect<void, ExecError>;
   readonly restore: (branch: string, name: string) => Effect.Effect<void, ExecError>;
@@ -142,6 +143,19 @@ export const live = Layer.effect(
         ].join("\n"),
       );
 
+    const releaseDirtyError = (branch: string, worktree: Worktree) =>
+      new ExecError(
+        "git",
+        ["release", branch],
+        1,
+        [
+          `${branch} is checked out at ${worktree.path} with local changes:`,
+          ...worktree.dirty.map((line) => `  ${line}`),
+          "",
+          `Commit, stash, or clean that worktree before releasing ${branch}.`,
+        ].join("\n"),
+      );
+
     const refs = Effect.fn("Git.refs")(function* () {
       const out = yield* run("git", [
         "for-each-ref",
@@ -269,6 +283,17 @@ export const live = Layer.effect(
     const backup = Effect.fn("Git.backup")((branch: string, name: string) =>
       run("git", ["branch", "-f", name, branch]).pipe(Effect.asVoid),
     );
+    const release = Effect.fn("Git.release")(function* (branch: string) {
+      const owner =
+        (yield* worktrees()).find(
+          (worktree) => worktree.branch === branch && worktree.path !== cfg.root,
+        ) ?? null;
+      if (!owner) return;
+      if (owner.dirty.length > 0) {
+        return yield* Effect.fail(releaseDirtyError(branch, owner));
+      }
+      return yield* runAt(owner.path, "git", ["checkout", "--detach", "HEAD"]).pipe(Effect.asVoid);
+    });
     const drop = Effect.fn("Git.drop")(function* (branch: string) {
       const owner =
         (yield* worktrees()).find(
@@ -311,6 +336,7 @@ export const live = Layer.effect(
       commits,
       novel,
       replay,
+      release,
       backup,
       drop,
       restore,
@@ -350,6 +376,7 @@ export const test = (opts: {
       commits: () => Effect.succeed([]),
       novel: (_parent, _branch, commits) => Effect.succeed(commits),
       replay: () => Effect.void,
+      release: () => Effect.void,
       backup: () => Effect.void,
       drop: () => Effect.void,
       restore: () => Effect.void,
diff --git a/src/services/Stack.ts b/src/services/Stack.ts
index 4b65e8d..47c7cfb 100644
--- a/src/services/Stack.ts
+++ b/src/services/Stack.ts
@@ -1636,6 +1636,11 @@ ${note}`;
             const stamp = yield* timestamp();
             const name = `backup/landed-${stamp}-${target}`;
             const hasLocalTarget = refs.some((item) => item.name === target);
+            const targetOwner = hasLocalTarget
+              ? ((yield* git.worktrees()).find(
+                  (worktree) => worktree.branch === target && worktree.path !== cfg.root,
+                ) ?? null)
+              : null;
             const next = scopedState.links.find((item) => item.parent === target)?.branch ?? null;
             const landed = new Set([reference(Number(pr.number)), String(target)]);
             const preRetargets = (yield* Effect.forEach(
@@ -1741,11 +1746,12 @@ ${note}`;
               { apply: false },
             );
             if (active) {
-              yield* ensureRepairableWorktrees(
-                plannedRepair.actions.flatMap((item) =>
+              yield* ensureRepairableWorktrees([
+                ...(targetOwner ? [target] : []),
+                ...plannedRepair.actions.flatMap((item) =>
                   item._tag === "Rebase" ? [String(item.branch)] : [],
                 ),
-              );
+              ]);
             }
             const actions = [
               ...(current === target ? [`${active ? "" : "would "}switch to ${root}`] : []),
@@ -1820,6 +1826,10 @@ ${note}`;
               }
               yield* beginPostMergeRepair();
               if (hasLocalTarget) {
+                if (targetOwner) {
+                  yield* step(`release ${target} worktree`);
+                  yield* git.release(target);
+                }
                 yield* step(`drop local ${target}`);
                 yield* git.drop(target);
               }
diff --git a/tests/stack.test.ts b/tests/stack.test.ts
index 93fd795..14a7756 100644
--- a/tests/stack.test.ts
+++ b/tests/stack.test.ts
@@ -90,6 +90,7 @@ const gitAndCodeHost = (service: Partial<Git.Interface & CodeHost.Interface>) =>
     commits: () => Effect.succeed([]),
     novel: (_parent, _branch, commits) => Effect.succeed(commits),
     replay: () => Effect.void,
+    release: () => Effect.void,
     backup: () => Effect.void,
     drop: () => Effect.void,
     restore: () => Effect.void,
@@ -830,7 +831,7 @@ const makeLand = (
   dirty: ReadonlyArray<string> = [],
   currentBranch = "stack-a",
   progress: Array<Progress.ProgressEvent> | null = null,
-  codeHost: Partial<CodeHost.Interface> = {},
+  codeHost: Partial<Git.Interface & CodeHost.Interface> = {},
   includeUnrelatedRoot = false,
   forkStackC = false,
 ) => {
@@ -993,6 +994,7 @@ const makeLand = (
               refs.set(branch, branchRef({ name: branch, head: `${branch}-2` }));
               bases.set(`${branch}:${parent}`, refs.get(parent)?.head ?? "");
             }),
+          release: (branch: string) => Effect.sync(() => void seen.push(`release ${branch}`)),
           backup: (branch: string, name: string) =>
             Effect.sync(() => void seen.push(`backup ${branch} ${name}`)),
           drop: (branch: string) => Effect.sync(() => void seen.push(`drop ${branch}`)),
@@ -1409,6 +1411,75 @@ describe("Git", () => {
     15_000,
   );
 
+  it.effect(
+    "release detaches a clean owning worktree",
+    () =>
+      Effect.gen(function* () {
+        const root = yield* tempDir();
+        const repo = join(root, "repo");
+        const sibling = join(root, "stack-b-worktree");
+
+        yield* mkdirp(repo);
+        yield* shell(repo, "git", ["init", "-b", "dev"]);
+        yield* shell(repo, "git", ["config", "user.email", "stack@example.com"]);
+        yield* shell(repo, "git", ["config", "user.name", "Stack Test"]);
+        yield* commitFile(repo, "base.txt", "base\n", "base");
+
+        yield* shell(repo, "git", ["checkout", "-b", "stack-b"]);
+        yield* commitFile(repo, "b.txt", "b1\n", "b1");
+        const stackBTip = yield* shell(repo, "git", ["rev-parse", "stack-b"]);
+        yield* shell(repo, "git", ["checkout", "dev"]);
+        yield* shell(repo, "git", ["worktree", "add", sibling, "stack-b"]);
+
+        const cfgLayer = StackConfig.layer({ root: repo, trunks: ["dev"] }).pipe(
+          Layer.provide(NodeServices.layer),
+        );
+
+        yield* Effect.gen(function* () {
+          const git = yield* Git.Service;
+          yield* git.release("stack-b");
+        }).pipe(Effect.provide(Git.live.pipe(Layer.provide(cfgLayer))));
+
+        expect(yield* shell(sibling, "git", ["branch", "--show-current"])).toBe("");
+        expect(yield* shell(sibling, "git", ["rev-parse", "HEAD"])).toBe(stackBTip);
+        expect(yield* shell(repo, "git", ["rev-parse", "--verify", "stack-b"])).toBe(stackBTip);
+      }).pipe(Effect.provide(platform)),
+    15_000,
+  );
+
+  it.effect(
+    "release no-ops when branch is not checked out elsewhere",
+    () =>
+      Effect.gen(function* () {
+        const root = yield* tempDir();
+        const repo = join(root, "repo");
+
+        yield* mkdirp(repo);
+        yield* shell(repo, "git", ["init", "-b", "dev"]);
+        yield* shell(repo, "git", ["config", "user.email", "stack@example.com"]);
+        yield* shell(repo, "git", ["config", "user.name", "Stack Test"]);
+        yield* commitFile(repo, "base.txt", "base\n", "base");
+
+        yield* shell(repo, "git", ["checkout", "-b", "stack-b"]);
+        yield* commitFile(repo, "b.txt", "b1\n", "b1");
+        const stackBTip = yield* shell(repo, "git", ["rev-parse", "stack-b"]);
+        yield* shell(repo, "git", ["checkout", "dev"]);
+
+        const cfgLayer = StackConfig.layer({ root: repo, trunks: ["dev"] }).pipe(
+          Layer.provide(NodeServices.layer),
+        );
+
+        yield* Effect.gen(function* () {
+          const git = yield* Git.Service;
+          yield* git.release("stack-b");
+        }).pipe(Effect.provide(Git.live.pipe(Layer.provide(cfgLayer))));
+
+        expect(yield* shell(repo, "git", ["branch", "--show-current"])).toBe("dev");
+        expect(yield* shell(repo, "git", ["rev-parse", "--verify", "stack-b"])).toBe(stackBTip);
+      }).pipe(Effect.provide(platform)),
+    15_000,
+  );
+
   it.effect("worktrees ignores prunable records before dirty checks", () => {
     const calls: Array<{ cwd: string; args: ReadonlyArray<string> }> = [];
     const proc = Layer.succeed(
@@ -3716,6 +3787,56 @@ describe("Stack", () => {
     }).pipe(Effect.provide(test.layer));
   });
 
+  it.effect("land apply releases a clean checked-out target before deleting it", () => {
+    const test = makeLand([], "dev", null, {
+      worktrees: () =>
+        Effect.succeed([
+          {
+            path: "/tmp/stack-a-worktree",
+            head: "stack-a-1",
+            branch: "stack-a",
+            dirty: [],
+          },
+        ]),
+    });
+
+    return Effect.gen(function* () {
+      const stack = yield* Stack;
+      yield* stack.land("stack-a", { apply: true });
+
+      const release = test.seen.indexOf("release stack-a");
+      const drop = test.seen.indexOf("drop stack-a");
+      expect(release).toBeGreaterThan(-1);
+      expect(drop).toBeGreaterThan(release);
+      expect(test.seen.indexOf("merge 4")).toBeLessThan(release);
+    }).pipe(Effect.provide(test.layer));
+  });
+
+  it.effect("land auto releases a clean checked-out target before deleting it", () => {
+    const test = makeLand([], "dev", null, {
+      worktrees: () =>
+        Effect.succeed([
+          {
+            path: "/tmp/stack-a-worktree",
+            head: "stack-a-1",
+            branch: "stack-a",
+            dirty: [],
+          },
+        ]),
+    });
+
+    return Effect.gen(function* () {
+      const stack = yield* Stack;
+      yield* stack.land("stack-a", { auto: true });
+
+      const release = test.seen.indexOf("release stack-a");
+      const drop = test.seen.indexOf("drop stack-a");
+      expect(release).toBeGreaterThan(-1);
+      expect(drop).toBeGreaterThan(release);
+      expect(test.seen.indexOf("wait 4 merged")).toBeLessThan(release);
+    }).pipe(Effect.provide(test.layer));
+  });
+
   it.effect("land auto can merge through a target PR", () => {
     const test = makeLand();
 
@@ -4461,6 +4582,56 @@ describe("Stack", () => {
     }).pipe(Effect.provide(test.layer));
   });
 
+  it.effect("land apply refuses a dirty target worktree before merging the root", () => {
+    const test = makeLand([], "dev", null, {
+      worktrees: () =>
+        Effect.succeed([
+          {
+            path: "/tmp/stack-a-worktree",
+            head: "stack-a-1",
+            branch: "stack-a",
+            dirty: ["?? dirty.txt"],
+          },
+        ]),
+    });
+
+    return Effect.gen(function* () {
+      const stack = yield* Stack;
+      const error = yield* Effect.flip(stack.land("stack-a", { apply: true }));
+
+      expect(error).toBeInstanceOf(StackOperationError);
+      expect(error.message).toContain("Cannot repair checked-out dirty worktree branches");
+      expect(error.message).toContain("stack-a -> /tmp/stack-a-worktree");
+      expect(error.message).toContain("?? dirty.txt");
+      expect(test.seen).toEqual([]);
+    }).pipe(Effect.provide(test.layer));
+  });
+
+  it.effect("land auto refuses a dirty target worktree before merging the root", () => {
+    const test = makeLand([], "dev", null, {
+      worktrees: () =>
+        Effect.succeed([
+          {
+            path: "/tmp/stack-a-worktree",
+            head: "stack-a-1",
+            branch: "stack-a",
+            dirty: ["?? dirty.txt"],
+          },
+        ]),
+    });
+
+    return Effect.gen(function* () {
+      const stack = yield* Stack;
+      const error = yield* Effect.flip(stack.land("stack-a", { auto: true }));
+
+      expect(error).toBeInstanceOf(StackOperationError);
+      expect(error.message).toContain("Cannot repair checked-out dirty worktree branches");
+      expect(error.message).toContain("stack-a -> /tmp/stack-a-worktree");
+      expect(error.message).toContain("?? dirty.txt");
+      expect(test.seen).toEqual([]);
+    }).pipe(Effect.provide(test.layer));
+  });
+
   it.effect(
     "land apply refuses a dirty descendant worktree before merging the root",
     () =>