git-story: register git pre-commit hook

ts/packages/git-story/README.md

@@ -10,14 +10,21 @@ Git runs any `git-<name>` binary on `PATH` as `git <name>`, so the
 $ cd ts/packages/git-story
 $ pnpm build
 $ npm link            # puts git-story on PATH
-$ git story init   # registers Copilot CLI hooks for this repo
+$ git story init   # registers Copilot CLI and git hooks for this repo
 $ git story hooks copilot user-prompt-submitted
 Hello World
+$ echo input | git story hooks git pre-commit a b
+git-story pre-commit: args=["a","b"] stdin="input\n"
 ```
 
 `init` writes the hooks to `.github/copilot/settings.local.json` and adds that
 file to `.git/info/exclude`, so it stays local to the clone.
 
+`init` also writes a `pre-commit` script to the git hooks directory (honors
+`core.hooksPath`). The script runs `exec git-story hooks git pre-commit "$@"`,
+so git's hook arguments and stdin reach the command unchanged. `init` does not
+overwrite a hook that it did not write.
+
 ## Trademarks
 
 This project may contain trademarks or logos for projects, products, or services. Authorized use of Microsoft

ts/packages/git-story/src/commands/hooks.ts

@@ -3,9 +3,19 @@
 
 import { Command } from "commander";
 
-// `hooks`: agent hook handlers. Placeholder output until story capture exists.
+// Reads all of stdin. Hooks get their payload here (Copilot JSON, or lines
+// git pipes to hooks such as pre-push). Returns "" when stdin is a terminal.
+async function readStdin(): Promise<string> {
+    if (process.stdin.isTTY) return "";
+    const chunks: Buffer[] = [];
+    for await (const chunk of process.stdin) chunks.push(chunk as Buffer);
+    return Buffer.concat(chunks).toString("utf8");
+}
+
+// `hooks`: agent and git hook handlers. Placeholder output until story
+// capture exists.
 export const hooksCommand = new Command("hooks").description(
-    "Agent hook handlers",
+    "Agent and git hook handlers",
 );
 
 hooksCommand
@@ -16,3 +26,19 @@ hooksCommand
     .action(() => {
         process.stdout.write("Hello World\n");
     });
+
+// `hooks git <hook> [args...]`: called by the scripts `init` writes to the
+// git hooks directory. Git's hook args and stdin are forwarded as-is.
+// Example: `git story hooks git pre-commit` with empty stdin.
+hooksCommand
+    .command("git")
+    .description("Git hook handlers")
+    .command("pre-commit")
+    .description("Handle the git pre-commit hook")
+    .argument("[args...]", "arguments git passed to the hook")
+    .action(async (args: string[]) => {
+        const input = await readStdin();
+        process.stdout.write(
+            `git-story pre-commit: args=${JSON.stringify(args)} stdin=${JSON.stringify(input)}\n`,
+        );
+    });

ts/packages/git-story/src/commands/init.ts

@@ -11,6 +11,15 @@ import path from "node:path";
 const COPILOT_SETTINGS = ".github/copilot/settings.local.json";
 const PROMPT_HOOK = "git story hooks copilot user-prompt-submitted";
 
+// Git hooks to register. Each gets a shell script that forwards git's args
+// and stdin to `git-story hooks git <hook>`. `exec` hands the script's stdin
+// to the command, so hooks that receive input (e.g. pre-push) keep it.
+const GIT_HOOKS = ["pre-commit"];
+// Marks scripts written by init, so init never overwrites a user's own hook.
+const GIT_HOOK_MARKER = "# git-story hook";
+const gitHookScript = (hook: string) =>
+    `#!/bin/sh\n${GIT_HOOK_MARKER}\nexec git-story hooks git ${hook} "$@"\n`;
+
 // Recursively sorts object keys so the settings file has a stable order.
 // Array order is kept. Example: {b:1,a:{d:2,c:3}} -> {a:{c:3,d:2},b:1}.
 function sortKeys(value: unknown): unknown {
@@ -78,4 +87,26 @@ export const initCommand = new Command("init")
             fs.appendFileSync(exclude, `${COPILOT_SETTINGS}\n`);
         }
         process.stdout.write(`Registered Copilot hooks in ${settingsPath}\n`);
+
+        // `--git-path hooks/<hook>` honors `core.hooksPath` and worktrees.
+        for (const hook of GIT_HOOKS) {
+            const hookPath = path.resolve(
+                git("rev-parse", "--git-path", `hooks/${hook}`),
+            );
+            if (
+                fs.existsSync(hookPath) &&
+                !fs.readFileSync(hookPath, "utf8").includes(GIT_HOOK_MARKER)
+            ) {
+                process.stderr.write(
+                    `Skipped ${hookPath}: existing hook not owned by git-story\n`,
+                );
+                process.exitCode = 1;
+                continue;
+            }
+            fs.mkdirSync(path.dirname(hookPath), { recursive: true });
+            fs.writeFileSync(hookPath, gitHookScript(hook), { mode: 0o755 });
+            process.stdout.write(
+                `Registered git ${hook} hook in ${hookPath}\n`,
+            );
+        }
     });