fix(server): show git's own output when a commit fails

apps/server/src/git/GitManager.test.ts

@@ -6041,7 +6041,7 @@ it.layer(layerGitManagerTest)("GitManager", (it) => {
       );
 
       expect(errorMessage).toContain("Git command failed in GitVcsDriver.commit.commit");
-      expect(errorMessage).not.toContain("hook: fail");
+      expect(errorMessage).toContain("hook: fail");
       expect(events).toEqual(
         expect.arrayContaining([
           expect.objectContaining({

apps/server/src/vcs/GitVcsDriverCore.test.ts

@@ -3415,6 +3415,44 @@ it.layer(layerTest)("GitVcsDriver core integration", (it) => {
       }),
     );
 
+    it.effect("surfaces the output of a hook that rejected the commit", () =>
+      Effect.gen(function* () {
+        const cwd = yield* makeTmpDir();
+        yield* initRepoWithCommit(cwd);
+        const driver = yield* GitVcsDriver.GitVcsDriver;
+        const fileSystem = yield* FileSystem.FileSystem;
+        const pathService = yield* Path.Path;
+
+        const hookOutput = "commit message is missing Signed-off-by";
+        yield* writeTextFile(
+          cwd,
+          ".git/hooks/pre-commit",
+          `#!/bin/sh\necho "${hookOutput}" >&2\nexit 1\n`,
+        );
+        yield* fileSystem.chmod(pathService.join(cwd, ".git/hooks/pre-commit"), 0o755);
+        yield* writeTextFile(cwd, "a.txt", "a\n");
+
+        const error = yield* driver
+          .commit(cwd, "Add a", "", { stage: { filePaths: ["a.txt"] } })
+          .pipe(Effect.flip);
+
+        assert.equal(error._tag, "GitCommandError");
+        assert.include(error.message, hookOutput);
+      }),
+    );
+
+    it.effect("says when there is nothing to commit", () =>
+      Effect.gen(function* () {
+        const cwd = yield* makeTmpDir();
+        yield* initRepoWithCommit(cwd);
+        const driver = yield* GitVcsDriver.GitVcsDriver;
+
+        const error = yield* driver.commit(cwd, "Empty", "").pipe(Effect.flip);
+
+        assert.include(error.message, "nothing to commit");
+      }),
+    );
+
     it.effect.each([false, true])(
       "preserves partial staging and split-index files (split: %s)",
       (split) =>

apps/server/src/vcs/GitVcsDriverCore.ts

@@ -491,6 +491,18 @@ function classifyGitFailure(stderr: string): GitCommandFailureReason | null {
   return null;
 }
 
+const COMMIT_FAILURE_OUTPUT_MAX_CHARS = 1_000;
+
+// `git commit` is local, so its output carries no remote URLs; it is surfaced
+// because a rejecting hook's own words are the only explanation of why.
+function commitFailureOutput({
+  stdout,
+  stderr,
+}: Pick<GitVcsDriver.ExecuteGitResult, "stdout" | "stderr">): string {
+  const output = (stderr.trim() || stdout.trim()).slice(-COMMIT_FAILURE_OUTPUT_MAX_CHARS);
+  return output.length > 0 ? output : "Git command exited with a non-zero status.";
+}
+
 function parseDefaultBranchFromRemoteHeadRef(value: string, remoteName: string): string | null {
   const trimmed = value.trim();
   const prefix = `refs/remotes/${remoteName}/`;
@@ -2250,10 +2262,20 @@ export const makeGitVcsDriverCore = Effect.fn("makeGitVcsDriverCore")(function*
             onStderrLine: (line: string) =>
               options.progress?.onOutputLine?.({ stream: "stderr", text: line }) ?? Effect.void,
           };
-    yield* executeGit("GitVcsDriver.commit.commit", cwd, args, {
+    const commitResult = yield* executeGit("GitVcsDriver.commit.commit", cwd, args, {
       ...(options?.timeoutMs !== undefined ? { timeoutMs: options.timeoutMs } : {}),
       ...(progress ? { progress } : {}),
-    }).pipe(Effect.asVoid);
+      allowNonZeroExit: true,
+    });
+    if (commitResult.exitCode !== 0) {
+      return yield* new GitCommandError({
+        ...gitCommandContext({ operation: "GitVcsDriver.commit.commit", cwd, args }),
+        detail: commitFailureOutput(commitResult),
+        ...(commitResult.exitCode === null ? {} : { exitCode: commitResult.exitCode }),
+        stdoutLength: commitResult.stdout.length,
+        stderrLength: commitResult.stderr.length,
+      });
+    }
     const commitSha = yield* runGitStdout("GitVcsDriver.commit.revParseHead", cwd, [
       "rev-parse",
       "HEAD",