feat: add pr create and comment (task 0010)

`pr create` takes --title (required), --body/--body-file, --base, --head,
--assignee, --reviewer, repeatable name-resolved --label, and --milestone.
An omitted --head defaults to the current local branch; an omitted --base to
the repository's default branch. Before creating, an existing open PR for the
same base/head pair short-circuits to `pull_request: { number, url, already:
true }` rather than opening a duplicate; only an open PR does, since a closed
one's branches are free to be proposed again.

`pr comment <n>` posts through the shared issue-comment endpoint and returns
the created comment as `comment: { number, author, created, body }` (ADR 0008),
reporting a 404 as PR_NOT_FOUND since the caller asked about a pull request.

That comment block is now built in one place (src/comment.ts) for both issue
and pr comment, as ADR 0008 requires them to stay identical.

test/pr-comment.test.ts

@@ -0,0 +1,145 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { startFixtureServer, type FixtureServer } from "./fixture-server.js";
+import { postedBody, runCliTest, tempFiles, testModeEnv } from "./harness.js";
+
+// Pull request comments go through the shared issue-comment endpoint.
+const COMMENTS_PATH = "/api/v1/repos/testowner/testrepo/issues/12/comments";
+
+let server: FixtureServer;
+const files = tempFiles();
+
+afterEach(async () => {
+  await server.close();
+  files.cleanup();
+});
+
+function createdComment(fields: Record<string, unknown> = {}): Record<string, unknown> {
+  return {
+    id: 900,
+    user: { login: "alexion" },
+    created_at: "2026-07-01T00:00:00Z",
+    body: "Looks good to me.",
+    pull_request_url: "http://127.0.0.1/testowner/testrepo/pulls/12",
+    ...fields,
+  };
+}
+
+function postedComment(): Record<string, unknown> {
+  return postedBody(server, COMMENTS_PATH);
+}
+
+describe("pr comment", () => {
+  it("posts the comment and renders number, author, created, and body", async () => {
+    server = await startFixtureServer([
+      { method: "POST", path: COMMENTS_PATH, status: 201, body: createdComment() },
+    ]);
+    const { stdout, exitCode } = await runCliTest(
+      ["pr", "comment", "12", "--body", "Looks good to me."],
+      { env: testModeEnv(server.url) },
+    );
+
+    expect(exitCode).toBe(0);
+    // The same `comment` block name as `issue comment`, per ADR 0008.
+    expect(stdout).toContain("comment:");
+    // `number` is the PR commented on, not the comment's own id.
+    expect(stdout).toContain("number: 12");
+    expect(stdout).toContain("author: alexion");
+    expect(stdout).toContain("body: Looks good to me.");
+    expect(stdout).not.toContain("900");
+    expect(postedComment()).toEqual({ body: "Looks good to me." });
+  });
+
+  it("reads the body from --body-file", async () => {
+    const path = files.write("comment.md", "From a file.");
+    server = await startFixtureServer([
+      { method: "POST", path: COMMENTS_PATH, status: 201, body: createdComment() },
+    ]);
+    const { exitCode } = await runCliTest(["pr", "comment", "12", "--body-file", path], {
+      env: testModeEnv(server.url),
+    });
+
+    expect(exitCode).toBe(0);
+    expect(postedComment()).toEqual({ body: "From a file." });
+  });
+
+  it("truncates a body over 800 chars in the output, with the inline hint", async () => {
+    const body = "z".repeat(1000);
+    server = await startFixtureServer([
+      { method: "POST", path: COMMENTS_PATH, status: 201, body: createdComment({ body }) },
+    ]);
+    const { stdout, exitCode } = await runCliTest(["pr", "comment", "12", "--body", body], {
+      env: testModeEnv(server.url),
+    });
+
+    expect(exitCode).toBe(0);
+    expect(stdout).toContain(
+      `... (truncated, ${body.length} chars total - use --full to see complete body)`,
+    );
+    // The posted body itself is never truncated — only its echo in the output.
+    expect(postedComment()).toEqual({ body });
+  });
+
+  it("echoes the untruncated body with --full", async () => {
+    const body = "z".repeat(1000);
+    server = await startFixtureServer([
+      { method: "POST", path: COMMENTS_PATH, status: 201, body: createdComment({ body }) },
+    ]);
+    const { stdout, exitCode } = await runCliTest(
+      ["pr", "comment", "12", "--body", body, "--full"],
+      { env: testModeEnv(server.url) },
+    );
+
+    expect(exitCode).toBe(0);
+    expect(stdout).toContain(body);
+    expect(stdout).not.toContain("truncated");
+  });
+
+  it("rejects a missing body before calling the API", async () => {
+    server = await startFixtureServer([]);
+    const { stdout, exitCode } = await runCliTest(["pr", "comment", "12"], {
+      env: testModeEnv(server.url),
+    });
+
+    expect(exitCode).toBe(2);
+    expect(stdout).toContain("code: VALIDATION_ERROR");
+    expect(stdout).toContain("--body");
+    expect(server.requests).toHaveLength(0);
+  });
+
+  it("rejects a missing pull request number before calling the API", async () => {
+    server = await startFixtureServer([]);
+    const { stdout, exitCode } = await runCliTest(["pr", "comment", "--body", "hi"], {
+      env: testModeEnv(server.url),
+    });
+
+    expect(exitCode).toBe(2);
+    expect(stdout).toContain("code: VALIDATION_ERROR");
+    expect(stdout).toContain("pull request number");
+    expect(server.requests).toHaveLength(0);
+  });
+
+  it("reports a nonexistent pull request as PR_NOT_FOUND, not ISSUE_NOT_FOUND", async () => {
+    server = await startFixtureServer([
+      { method: "POST", path: COMMENTS_PATH, status: 404, body: { message: "Not Found" } },
+    ]);
+    const { stdout, exitCode } = await runCliTest(["pr", "comment", "12", "--body", "hi"], {
+      env: testModeEnv(server.url),
+    });
+
+    expect(exitCode).toBe(1);
+    // The shared endpoint lives under /issues/, but the caller asked about a PR.
+    expect(stdout).toContain("code: PR_NOT_FOUND");
+    expect(stdout).toContain("Pull request #12");
+  });
+
+  it("prints help with --help without calling the API", async () => {
+    server = await startFixtureServer([]);
+    const { stdout, exitCode } = await runCliTest(["pr", "comment", "--help"], {
+      env: testModeEnv(server.url),
+    });
+
+    expect(exitCode).toBe(0);
+    expect(stdout).toContain("usage: gitea-axi pr comment <number>");
+    expect(server.requests).toHaveLength(0);
+  });
+});