diff --git a/packages/cli/tests/host.test.mjs b/packages/cli/tests/host.test.mjs
index 0a5d68253..13a621ae9 100644
--- a/packages/cli/tests/host.test.mjs
+++ b/packages/cli/tests/host.test.mjs
@@ -559,3 +559,55 @@ test("bus-service.sh pins the claude binary, refuses one the unit can't carry, a
   assert.match(none.stdout, /^# MOSAIC_CLAUDE_BIN unset: no claude on PATH at install time$/m);
   assert.doesNotMatch(none.stdout, /@CLAUDE_ENV@/);
 });
+
+// Row 72 (#1566): mutants row 68's tests left alive. A directory is -x, so
+// only the -f check keeps a directory pin out of the unit; the default pin
+// keeps a symlink as given, so a claude that updates through it is followed.
+test("bus-service.sh refuses a directory pin and keeps a symlink default unresolved", (t) => {
+  const dir = tmp(t);
+  const script = join(REPO, "scripts", "bus-service.sh");
+  const pinned = (out) => out.match(/^Environment=MOSAIC_CLAUDE_BIN=(.*)$/m)?.[1];
+  const tools = join(dir, "tools");
+  mkdirSync(tools);
+  symlinkSync(process.execPath, join(tools, "node"));
+  for (const tool of ["dirname", "sed", "readlink"]) {
+    const at = ["/usr/bin", "/bin"].map((d) => join(d, tool)).find((p) => existsSync(p));
+    symlinkSync(at, join(tools, tool));
+  }
+  const bash = ["/usr/bin/bash", "/bin/bash"].find((p) => existsSync(p));
+  const run = (args, bin) => spawnSync(bash, [script, ...args], { encoding: "utf8", env: { PATH: `${bin}:${tools}`, HOME: dir } });
+
+  // --claude DIR: a directory passes -x and fails -f.
+  const pinDir = join(dir, "claude-dir");
+  mkdirSync(pinDir);
+  chmodSync(pinDir, 0o755);
+  let r = run(["render", "--claude", pinDir], join(dir, "empty"));
+  assert.equal(r.status, 1);
+  assert.match(r.stderr, /not an executable file/);
+  assert.equal(r.stdout, "");
+
+  // A directory named claude on PATH: bash's `command -v` never returns a
+  // directory, so the default finds no claude and pins nothing. It never
+  // pins the directory.
+  const dirBin = join(dir, "dir-bin");
+  mkdirSync(join(dirBin, "claude"), { recursive: true });
+  chmodSync(join(dirBin, "claude"), 0o755);
+  r = run(["render"], dirBin);
+  assert.equal(r.status, 0, r.stderr);
+  assert.match(r.stderr, /no claude on PATH; MOSAIC_CLAUDE_BIN left unset/);
+  assert.equal(pinned(r.stdout), undefined);
+  assert.ok(!r.stdout.includes(join(dirBin, "claude")));
+
+  // A symlink named claude on PATH: the pin is the link, not its target.
+  const real = join(dir, "versions", "claude-9.9.9");
+  mkdirSync(dirname(real));
+  writeFileSync(real, '#!/bin/sh\necho "9.9.9 (Claude Code)"\n');
+  chmodSync(real, 0o755);
+  const linkBin = join(dir, "link-bin");
+  mkdirSync(linkBin);
+  symlinkSync(real, join(linkBin, "claude"));
+  r = run(["render"], linkBin);
+  assert.equal(r.status, 0, r.stderr);
+  assert.equal(pinned(r.stdout), join(linkBin, "claude"));
+  assert.ok(!r.stdout.includes(real), "the target never reaches the unit");
+});
diff --git a/packages/harness/tests/claude-session.test.mjs b/packages/harness/tests/claude-session.test.mjs
index eb680836d..213c811e8 100644
--- a/packages/harness/tests/claude-session.test.mjs
+++ b/packages/harness/tests/claude-session.test.mjs
@@ -215,6 +215,50 @@ test("claude adapter: MOSAIC_CLAUDE_BIN wins over PATH and must be an absolute e
   }
 });
 
+// Row 72 (#1566): a directory pin exits 2 with the adapter's own message,
+// not 126 at exec; a pin under a directory whose name has a space runs,
+// which needs "$CLAUDE" quoted.
+test("claude adapter: a directory pin exits 2 before it runs; a pin with a space runs", (t) => {
+  const dir = scratch(t);
+  mkdirSync(join(dir, "bin"));
+  const stand = (p, word) => {
+    writeFileSync(p, `#!/bin/sh\necho ${word} > "$WHO_OUT"\necho ok\n`);
+    chmodSync(p, 0o755);
+    return p;
+  };
+  stand(join(dir, "bin", "claude"), "path");
+  for (const f of ["prompt.md", "settings.json", "mcp.json"]) writeFileSync(join(dir, f), "{}");
+  const run = (bin) => spawnSync("/bin/sh", [ADAPTER], {
+    encoding: "utf8",
+    stdio: ["ignore", "pipe", "pipe"],
+    env: {
+      PATH: `${join(dir, "bin")}:/usr/bin:/bin`,
+      WHO_OUT: join(dir, "who"),
+      MOSAIC_SYSTEM_PROMPT_FILE: join(dir, "prompt.md"),
+      MOSAIC_REQUEST: "x",
+      MOSAIC_WORKSPACE: join(dir, "ws"),
+      MOSAIC_SESSION_DIR: join(dir, "session"),
+      MOSAIC_MODEL: "claude-sonnet-5-5",
+      MOSAIC_CLAUDE_SETTINGS: join(dir, "settings.json"),
+      MOSAIC_CLAUDE_MCP_CONFIG: join(dir, "mcp.json"),
+      MOSAIC_CLAUDE_BIN: bin,
+    },
+  });
+  const pinDir = join(dir, "claude-dir");
+  mkdirSync(pinDir);
+  chmodSync(pinDir, 0o755);
+  let r = run(pinDir);
+  assert.equal(r.status, 2, r.stderr);
+  assert.match(r.stderr, /MOSAIC_CLAUDE_BIN is not an executable file/);
+  assert.equal(existsSync(join(dir, "who")), false);
+
+  mkdirSync(join(dir, "Claude Code"));
+  const spaced = stand(join(dir, "Claude Code", "claude"), "spaced");
+  r = run(spaced);
+  assert.equal(r.status, 0, r.stderr);
+  assert.equal(readFileSync(join(dir, "who"), "utf8").trim(), "spaced");
+});
+
 test("claude: CLAUDE.md files and auto-memory don't reach the model; without --restricted they do", { skip }, async (t) => {
   const { dir, workspace, env } = await session(t, []);
   const slug = realpathSync(workspace).replace(/[/.]/g, "-");