diff --git a/src/cli.ts b/src/cli.ts
index 9f06d115c..09712e88e 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -30,7 +30,7 @@ import { asksForTrail, brand, cmd, graftNotice, PACKAGE_FOR, setBrand, strandedR
 import { branchDiff } from "./cloud/diff.js";
 import { openBrowser } from "./util/browser.js";
 import { committedAtBase, learningsAtBase, teammateEdits, withBaseLearnings } from "./check/learning-edits.js";
-import { CACHE_DIR, contextDirFor } from "./context/node-file.js";
+import { CACHE_DIR, contextDirFor, gitIgnoresDirectory } from "./context/node-file.js";
 import { loadGraphCached } from "./graph/load.js";
 import { ensureFreshChildren, ensureFreshGraph, refreshNote } from "./graph/refresh.js";
 import { isWorkspaceBuildRoot, readWorkspace } from "./graph/workspace.js";
@@ -821,8 +821,10 @@ grouped(program.command("build"), GROUP.setup)
     const rel = relative(process.cwd(), g.contextDir) || "graft";
     if (process.env.GRAFT_NO_GITIGNORE) {
       console.log(`  ${rel}/ is a local cache: add it to your gitignore if you want it untracked.`);
+    } else if (gitIgnoresDirectory(buildRoot, g.contextDir)) {
+      console.log(`  ${rel}/ is git-ignored. Teammates run \`${cmd("graft build")}\` to get their own cache.`);
     } else {
-      console.log(`  ${rel}/ is git-ignored (added automatically), a local cache; teammates run \`${cmd("graft build")}\` to get their own.`);
+      console.error(`  ${rel}/ is a local cache. Git did not confirm that it is ignored. Check before committing.`);
     }
 
     // #127: a --deep run whose LLM calls failed used to print the same success
diff --git a/src/context/node-file.ts b/src/context/node-file.ts
index 3461ffa8a..90f0e5416 100644
--- a/src/context/node-file.ts
+++ b/src/context/node-file.ts
@@ -183,7 +183,7 @@ export function ensureGitignored(root: string, contextDir: string, note = GRAPH_
   // a parent `.gitignore` or `core.excludesFile`. Then there is nothing to add, and appending
   // would dirty the checkout again on every build for a user who keeps tooling noise out of
   // the tracked `.gitignore` on purpose.
-  if (gitAlreadyIgnores(root, bare)) return;
+  if (gitIgnoresDirectory(root, contextDir)) return;
   const gap = current === "" ? "" : current.endsWith("\n") ? "\n" : "\n\n";
   const block = `${gap}# ${note}\n${entry}\n`;
   try { writeFileSync(path, current + block); } catch { /* best-effort — build already succeeded */ }
@@ -196,15 +196,16 @@ const GIT_REPO_ENV = [
   "GIT_DIR", "GIT_WORK_TREE", "GIT_INDEX_FILE", "GIT_COMMON_DIR", "GIT_OBJECT_DIRECTORY", "GIT_NAMESPACE",
 ];
 
-/** True when `root` is a git work tree whose ignore rules (every source git reads: `.gitignore`
- *  files, `.git/info/exclude`, `core.excludesFile`) already cover the directory `rel/`. Any
- *  failure (git missing, not a repo, timeout) answers false, so the caller falls back to
- *  writing the entry. The trailing slash makes git treat the path as a directory, so dir-only
+/** True when Git confirms its ignore rules cover the directory inside `root`.
+ *  A missing Git, timeout or other failed check answers false. The trailing slash
+ *  makes git treat the path as a directory, so dir-only
  *  patterns like `graft/` match. A negation rule (an allowlist `.gitignore` that re-includes
  *  directories) can judge a not-yet-created path differently from an existing one, so callers
  *  create the dir first. `core.fsmonitor` is off because it would run a command named by the
  *  repo's own config. */
-function gitAlreadyIgnores(root: string, rel: string): boolean {
+export function gitIgnoresDirectory(root: string, directory: string): boolean {
+  const rel = relPosix(root, directory);
+  if (!rel || rel === ".." || rel.startsWith("../") || isAbsolute(rel)) return false;
   try {
     const env = { ...process.env };
     for (const k of GIT_REPO_ENV) delete env[k];
diff --git a/test/cli-cache-ignore.test.ts b/test/cli-cache-ignore.test.ts
new file mode 100644
index 000000000..72d757f1b
--- /dev/null
+++ b/test/cli-cache-ignore.test.ts
@@ -0,0 +1,37 @@
+import assert from "node:assert/strict";
+import { execFileSync } from "node:child_process";
+import { mkdirSync, rmdirSync, rmSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { test } from "node:test";
+import { homeEnv, runCli, tmpRepo } from "./helpers.js";
+
+test("build reports whether Git ignores the cache after a failed ignore write", () => {
+  const root = tmpRepo("cli-cache-ignore");
+  const env = {
+    ...homeEnv(root),
+    DO_NOT_TRACK: "1",
+    GRAFT_NO_GITIGNORE: undefined,
+    GIT_CONFIG_GLOBAL: join(root, "empty-git-config"),
+    GIT_CONFIG_NOSYSTEM: "1",
+  };
+  const ignore = join(root, ".gitignore");
+
+  try {
+    execFileSync("git", ["init", "-q", "--template="], { cwd: root, env });
+    writeFileSync(join(root, "app.js"), "export function hello() { return 1; }\n");
+    mkdirSync(ignore); // Make the write fail even if tests run with elevated permissions.
+
+    const unignored = runCli(["build", root, "--no-ignore"], { env, timeoutMs: 20_000 });
+    assert.equal(unignored.status, 0, unignored.describe());
+    assert.doesNotMatch(unignored.stdout, /is git-ignored/, unignored.describe());
+    assert.match(unignored.stderr, /Git did not confirm that it is ignored/, unignored.describe());
+
+    rmdirSync(ignore);
+    const ignored = runCli(["build", root, "--no-ignore"], { env, timeoutMs: 20_000 });
+    assert.equal(ignored.status, 0, ignored.describe());
+    assert.match(ignored.stdout, /is git-ignored/, ignored.describe());
+    execFileSync("git", ["check-ignore", "-q", "--", "graft/"], { cwd: root, env });
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});