fix(ci-drift): paginate open issues to prevent duplicate [ci-drift] issues

The find_open_issue() helper only fetched one page of open issues
(limit=50). When the existing [ci-drift] tracking issue fell beyond
page 1, the caller POSTed a duplicate instead of updating the existing
one.

Fix: loop over pages until the title is found or the result set is
exhausted (page returns <50 items). API errors propagate loud via
ApiError as before.

Adds two regression tests:
- test_find_open_issue_paginates_to_page_2
- test_find_open_issue_stops_at_last_page

Fixes issue-403.

.gitea/scripts/ci-required-drift.py

@@ -552,23 +552,34 @@ def find_open_issue(title: str) -> dict | None:
     hourly; failing one cycle loudly is strictly better than silently
     duplicating.
 
-    Gitea issue search returns at most page=50 per page; one page is
-    enough as long as `[ci-drift]` issues are a tiny minority. (See
-    follow-up issue for Link-header pagination.)
+    Paginates through all open issues (limit=50 per page) until the
+    title is found or the result set is exhausted. Previously only one
+    page was fetched, causing duplicate [ci-drift] issues when the
+    existing tracking issue fell beyond page 1.
     """
-    _, results = api(
-        "GET",
-        f"/repos/{OWNER}/{NAME}/issues",
-        query={"state": "open", "type": "issues", "limit": "50"},
-    )
-    if not isinstance(results, list):
-        raise ApiError(
-            f"issue search returned non-list body (got {type(results).__name__})"
+    page = 1
+    while True:
+        _, results = api(
+            "GET",
+            f"/repos/{OWNER}/{NAME}/issues",
+            query={
+                "state": "open",
+                "type": "issues",
+                "limit": "50",
+                "page": str(page),
+            },
         )
-    for issue in results:
-        if issue.get("title") == title:
-            return issue
-    return None
+        if not isinstance(results, list):
+            raise ApiError(
+                f"issue search returned non-list body (got {type(results).__name__})"
+            )
+        for issue in results:
+            if issue.get("title") == title:
+                return issue
+        # Fewer than limit results means last page reached.
+        if len(results) < 50:
+            return None
+        page += 1
 
 
 def render_body(branch: str, findings: list[str], debug: dict) -> str:

tests/test_ci_required_drift.py

@@ -584,6 +584,54 @@ def test_find_open_issue_raises_on_transient_error(drift_module, monkeypatch):
         drift_module.find_open_issue("[ci-drift] foo")
 
 
+# --------------------------------------------------------------------------
+# Pagination: search beyond page 1 so an existing issue on any page is found
+# --------------------------------------------------------------------------
+def test_find_open_issue_paginates_to_page_2(drift_module, monkeypatch):
+    """Issue exists on page 2 → paginate and find it."""
+    target = {"number": 99, "title": "[ci-drift] foo"}
+    filler = [{"number": i, "title": f"other-{i}"} for i in range(1, 51)]
+
+    class PaginatedStub:
+        def __init__(self):
+            self.calls = []
+
+        def __call__(self, method, path, *, body=None, query=None, expect_json=True):
+            self.calls.append((method, path, body, query))
+            page = int((query or {}).get("page", "1"))
+            if page == 1:
+                return 200, filler
+            if page == 2:
+                return 200, [target]
+            return 200, []
+
+    stub = PaginatedStub()
+    monkeypatch.setattr(drift_module, "api", stub)
+    assert drift_module.find_open_issue("[ci-drift] foo") == target
+    assert len(stub.calls) == 2
+
+
+def test_find_open_issue_stops_at_last_page(drift_module, monkeypatch):
+    """No match across pages → stop when a page has <50 results."""
+    filler = [{"number": i, "title": f"other-{i}"} for i in range(1, 51)]
+
+    class PaginatedStub:
+        def __init__(self):
+            self.calls = []
+
+        def __call__(self, method, path, *, body=None, query=None, expect_json=True):
+            self.calls.append((method, path, body, query))
+            page = int((query or {}).get("page", "1"))
+            if page == 1:
+                return 200, filler
+            return 200, []
+
+    stub = PaginatedStub()
+    monkeypatch.setattr(drift_module, "api", stub)
+    assert drift_module.find_open_issue("[ci-drift] foo") is None
+    assert len(stub.calls) == 2
+
+
 # --------------------------------------------------------------------------
 # Idempotent path: existing issue is PATCHed, NOT duplicated
 # --------------------------------------------------------------------------