diff --git a/modules/gitea/client.ts b/modules/gitea/client.ts
index 07dc481..61aba60 100644
--- a/modules/gitea/client.ts
+++ b/modules/gitea/client.ts
@@ -278,6 +278,42 @@ export class GiteaClient {
     }
   }
 
+  /** The directories holding these files that hold a `module.json` at a commit (novox/hq issue 278).
+   *
+   *  **Whether a directory is a module is a fact of the repository, not of the merge.** The mesh read a
+   *  changed file as shared code unless its directory was a module it held or the merge also changed
+   *  that directory's manifest; a change to the catalogue's reference module, which no machine holds,
+   *  rebuilt all 103 modules built from the repository. So every directory above a changed file — never
+   *  the root — is looked up at the merge commit, and the ones holding a manifest are said.
+   *
+   *  `null` when there are more than `most` directories to look at: not said, and the mesh keeps its old
+   *  rule, which rebuilds too much rather than too little. A failed lookup throws, for the same reason. */
+  async moduleDirsAt(owner: string, repo: string, sha: string, paths: string[], most = 300): Promise<string[] | null> {
+    const dirs = directoriesAbove(paths);
+    if (dirs.length > most) return null;
+    const out: string[] = [];
+    for (const dir of dirs) {
+      if (await this.exists(`/repos/${owner}/${repo}/contents/${encodePath(dir + "/module.json")}?ref=${encodeURIComponent(sha)}`)) {
+        out.push(dir);
+      }
+    }
+    return out;
+  }
+
+  /** Whether the forge has something at a path: true for an answer, false for a 404, thrown otherwise. */
+  private async exists(path: string): Promise<boolean> {
+    let token = await this.tokens.current();
+    let res = await this.send(path, {}, token);
+    if (res.status === 401) {
+      token = await this.tokens.renew(token);
+      res = await this.send(path, {}, token);
+    }
+    if (res.status === 404) return false;
+    if (!res.ok) throw new Error(`Gitea API ${path}: ${res.status} ${await res.text()}`);
+    await res.body?.cancel();
+    return true;
+  }
+
   async createPullRequest(
     owner: string,
     repo: string,
@@ -616,3 +652,21 @@ export function movedSince(repos: GiteaRepo[], floor: string): GiteaRepo[] {
   const at = Date.parse(floor);
   return repos.filter((r) => !r.updated_at || !(Date.parse(r.updated_at) < at));
 }
+
+/** Every directory above these files, from the repository's root, the root itself left out; sorted. */
+export function directoriesAbove(paths: string[]): string[] {
+  const dirs = new Set<string>();
+  for (const raw of paths) {
+    const parts = raw.replace(/^\/+/, "").split("/");
+    for (let i = 1; i < parts.length; i++) {
+      const dir = parts.slice(0, i).join("/");
+      if (dir !== "") dirs.add(dir);
+    }
+  }
+  return [...dirs].sort();
+}
+
+/** A repository path for the forge's URL: each segment escaped, the slashes kept. */
+function encodePath(path: string): string {
+  return path.split("/").map(encodeURIComponent).join("/");
+}
diff --git a/modules/gitea/index.ts b/modules/gitea/index.ts
index 99eff32..57f5f48 100644
--- a/modules/gitea/index.ts
+++ b/modules/gitea/index.ts
@@ -107,6 +107,18 @@ async function pollMerged(client: GiteaClient): Promise<void> {
         // directory moved, and without this every module built from a repository is rebuilt for a
         // change to any of them (novox/hq 04-ISSUES/131).
         const changed = await client.listPullFiles(repo.owner, repo.name, pull.number);
+        // Which of the directories they are in hold a module at the merge commit (novox/hq issue 278): a
+        // change inside one is that module's, held or not, and only a file in none is shared code. Not
+        // said when the list is cut or the forge could not be asked; the mesh then keeps its old rule.
+        let moduleDirs: string[] | null = null;
+        if (!changed.truncated) {
+          try {
+            moduleDirs = await client.moduleDirsAt(repo.owner, repo.name, pull.merge_commit_sha, changed.paths);
+          } catch (err) {
+            console.error(`[gitea] ${repo.full_name}#${pull.number}: which directories hold a module could not be read, ` +
+              `so the mesh reads its files by the old rule — ${err instanceof Error ? err.message : String(err)}`);
+          }
+        }
         await emit("pull.merged", {
           owner: repo.owner,
           repo: repo.name,
@@ -123,6 +135,7 @@ async function pollMerged(client: GiteaClient): Promise<void> {
           // Which of them the merge deleted (novox/hq ADR 0236): a module whose manifest went is forgotten,
           // not built.
           removed: changed.removed,
+          ...(moduleDirs ? { module_dirs: moduleDirs, module_dirs_said: true } : {}),
         });
         // Said, because a trigger that fires silently is indistinguishable from one that did not
         // fire (novox/hq 04-ISSUES/131) — this line is how an operator knows the mesh was told.
diff --git a/modules/gitea/test/pages.test.ts b/modules/gitea/test/pages.test.ts
index f389ab2..063cf32 100644
--- a/modules/gitea/test/pages.test.ts
+++ b/modules/gitea/test/pages.test.ts
@@ -36,3 +36,38 @@ test("a pass asks only the repositories that moved since the last look, every on
   assert.deepEqual(movedSince(repos, "2026-10-05T16:09:00.000Z").map((r) => r.name), ["new", "unknown"]);
   assert.deepEqual(movedSince(repos, "2026-10-05T18:10:02+02:00").map((r) => r.name), ["new", "unknown"], "an offset is a moment, not a string");
 });
+
+test("the directories above a merge's files that hold a module at the commit are said, the root never", async () => {
+  const { directoriesAbove } = await import("../client.ts");
+  assert.deepEqual(directoriesAbove(["modules/showcase/index.ts", "modules/showcase/daemon/x.ts", "README.md", "/modules/lib/a.go"]),
+    ["modules", "modules/lib", "modules/showcase", "modules/showcase/daemon"]);
+  const asked: string[] = [];
+  const server = createServer((req, res) => {
+    const url = new URL(req.url ?? "", "http://x");
+    asked.push(`${url.pathname}@${url.searchParams.get("ref")}`);
+    const held = ["/api/v1/repos/novox/mesh-catalog/contents/modules/showcase/module.json"];
+    res.statusCode = held.includes(url.pathname) ? 200 : 404;
+    res.end(res.statusCode === 200 ? "{}" : '{"message":"not found"}');
+  });
+  await new Promise<void>((r) => server.listen(0, r));
+  const port = (server.address() as any).port;
+  const client = new GiteaClient(`http://127.0.0.1:${port}`, "t");
+  const got = await client.moduleDirsAt("novox", "mesh-catalog", "abc", ["modules/showcase/index.ts", "modules/lib/x.go"]);
+  const capped = await client.moduleDirsAt("novox", "mesh-catalog", "abc", ["a/b/c/d.ts"], 2);
+  server.close();
+  assert.deepEqual(got, ["modules/showcase"], "a directory holding a manifest is a module; one holding none is not");
+  assert.ok(asked.every((a) => a.endsWith("@abc")), "looked up at the merge commit");
+  assert.equal(capped, null, "past the bound it is not said, and the mesh keeps its old rule");
+});
+
+test("a lookup the forge refuses is thrown, not read as no module", async () => {
+  const server = createServer((_req, res) => {
+    res.statusCode = 500;
+    res.end("down");
+  });
+  await new Promise<void>((r) => server.listen(0, r));
+  const port = (server.address() as any).port;
+  const client = new GiteaClient(`http://127.0.0.1:${port}`, "t");
+  await assert.rejects(client.moduleDirsAt("novox", "mesh-catalog", "abc", ["modules/x/y.ts"]));
+  server.close();
+});