feat: github_merge_pr: optional subject/body (gh pr merge --subject/--body), refused on rebase, shown in dry run

tests/test_write_tools.py

@@ -429,6 +429,89 @@ async def test_merge_pr_validates_method():
     fake.assert_not_called()
 
 
+async def test_merge_pr_squash_with_subject():
+    tool = _by_name("github_merge_pr")
+    fake = AsyncMock(return_value=(0, "Merged", ""))
+    with patch("ghplugin.write_tools.run_gh", fake):
+        await tool.ainvoke(
+            {
+                "repo": "o/n",
+                "number": 9,
+                "method": "squash",
+                "subject": "chore: release v0.16.0 (#48)",
+                "confirm": True,
+            }
+        )
+    args = fake.call_args.args[0]
+    assert args == ["pr", "merge", "9", "--repo", "o/n", "--squash", "--subject", "chore: release v0.16.0 (#48)"]
+
+
+async def test_merge_pr_merge_with_subject_body_and_delete_branch():
+    tool = _by_name("github_merge_pr")
+    fake = AsyncMock(return_value=(0, "Merged", ""))
+    with patch("ghplugin.write_tools.run_gh", fake):
+        await tool.ainvoke(
+            {
+                "repo": "o/n",
+                "number": 9,
+                "method": "merge",
+                "delete_branch": True,
+                "subject": "a subject",
+                "body": "a body",
+                "confirm": True,
+            }
+        )
+    args = fake.call_args.args[0]
+    assert args[-6:] == ["--merge", "--delete-branch", "--subject", "a subject", "--body", "a body"]
+
+
+async def test_merge_pr_rebase_refuses_subject():
+    tool = _by_name("github_merge_pr")
+    fake = AsyncMock()
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke({"repo": "o/n", "number": 9, "method": "rebase", "subject": "x", "confirm": True})
+    assert out.startswith("Error") and "rebase" in out
+    fake.assert_not_called()
+
+
+async def test_merge_pr_rebase_refuses_body_on_dry_run():
+    tool = _by_name("github_merge_pr")
+    fake = AsyncMock()
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke({"repo": "o/n", "number": 9, "method": "rebase", "body": "x", "dry_run": True})
+    assert out.startswith("Error") and "rebase" in out
+    fake.assert_not_called()
+
+
+async def test_merge_pr_dry_run_shows_subject_and_body():
+    tool = _by_name("github_merge_pr")
+    fake = AsyncMock()
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke(
+            {
+                "repo": "o/n",
+                "number": 48,
+                "method": "squash",
+                "subject": "chore: release v0.16.0 (#48)",
+                "body": "release notes",
+                "dry_run": True,
+            }
+        )
+    assert out.startswith("DRY RUN")
+    assert 'subject "chore: release v0.16.0 (#48)"' in out
+    assert 'body "release notes"' in out
+    fake.assert_not_called()
+
+
+async def test_merge_pr_dry_run_without_subject_body_unchanged():
+    tool = _by_name("github_merge_pr")
+    fake = AsyncMock()
+    with patch("ghplugin.write_tools.run_gh", fake):
+        out = await tool.ainvoke({"repo": "o/n", "number": 9, "dry_run": True})
+    assert out == "DRY RUN — would merge PR #9 in o/n via squash. Re-call with confirm=true to do it."
+    fake.assert_not_called()
+
+
 # --- github_close / reopen ---------------------------------------------------
 
 

write_tools.py

@@ -289,6 +289,8 @@ async def github_merge_pr(
         repo: str = "",
         method: str = "squash",
         delete_branch: bool = False,
+        subject: str = "",
+        body: str = "",
         dry_run: bool = False,
         confirm: bool = False,
     ) -> str:
@@ -299,6 +301,11 @@ async def github_merge_pr(
             number: PR number.
             method: ``squash`` (default), ``merge``, or ``rebase``.
             delete_branch: Delete the head branch after merging (default False).
+            subject: Merge-commit subject line. Squash/merge only — refused on rebase,
+                which GitHub ignores. A single-commit squash uses that COMMIT's subject,
+                not the PR title, unless subject is set — so fixing the PR title alone
+                does not fix the subject that lands on main.
+            body: Merge-commit body. Squash/merge only — refused on rebase.
             dry_run: If true, report what WOULD be merged without merging.
             confirm: Must be true to actually merge — a guard against accidental or
                 autonomous merges even when the per-agent write gate is on.
@@ -310,10 +317,18 @@ async def github_merge_pr(
             return err
         if method not in ("squash", "merge", "rebase"):
             return f"Error: method must be 'squash', 'merge', or 'rebase' (got {method!r})."
+        if method == "rebase" and (subject or body):
+            return "Error: subject/body only apply to squash or merge — GitHub ignores them on a rebase merge."
         if dry_run:
             extra = " and delete its branch" if delete_branch else ""
+            detail = ""
+            if subject:
+                detail += f' with subject "{subject}"'
+            if body:
+                detail += f'{" and" if subject else " with"} body "{body}"'
             return (
-                f"DRY RUN — would merge PR #{number} in {repo} via {method}{extra}. Re-call with confirm=true to do it."
+                f"DRY RUN — would merge PR #{number} in {repo} via {method}{extra}{detail}. "
+                "Re-call with confirm=true to do it."
             )
         if not confirm:
             return (
@@ -323,6 +338,10 @@ async def github_merge_pr(
         args = ["pr", "merge", str(number), "--repo", repo, f"--{method}"]
         if delete_branch:
             args.append("--delete-branch")
+        if subject:
+            args += ["--subject", subject]
+        if body:
+            args += ["--body", body]
         rc, out, serr = await run_gh(args)
         if gh_err := check_gh_error(rc, serr, repo=repo):
             return gh_err