Page to the end when searching for an existing PR

find_pull_request read only the newest 50 per state, so once a repo
passed that many pull requests a "not found" would mean "not in the
newest page" — and the A3 reconciler would read that as "the PR was
never opened" and open a duplicate. Exactly the side effect the
intent log exists to prevent.

It now pages until a short page proves the end, and raises rather
than answering "absent" from an incomplete search; the reconciler
turns that into unverifiable and gates to the human.

Found while wiring CI: every CI run opens a PR in the sandbox, so the
threshold would have been crossed in weeks rather than never.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nisse-dev/tests/test_gitea.py

@@ -4,6 +4,7 @@ import httpx
 import pytest
 
 from nisse_dev.gitea import (
+    PR_PAGE_SIZE,
     Comment,
     GiteaClient,
     GiteaError,
@@ -61,27 +62,58 @@ def test_open_pull_request_posts_expected_body() -> None:
 
 
 def test_find_pull_request_matches_head_branch() -> None:
-    def handler(request: httpx.Request) -> httpx.Response:
-        if request.url.params.get("state") == "open":
-            return httpx.Response(200, json=[pr_json(3, "other")])
-        return httpx.Response(200, json=[])
-
+    handler = lambda request: httpx.Response(200, json=[pr_json(3, "other")])
     assert client(handler).find_pull_request("o/r", "milestone-1") is None
 
 
-def test_find_pull_request_also_checks_closed() -> None:
+def test_find_pull_request_also_finds_closed() -> None:
     # A crash after opening must not be answered with "nothing open, open
     # another" — the effect already happened.
-    def handler(request: httpx.Request) -> httpx.Response:
-        if request.url.params.get("state") == "open":
-            return httpx.Response(200, json=[])
-        return httpx.Response(200, json=[pr_json(4, "milestone-1", "closed")])
-
+    handler = lambda request: httpx.Response(
+        200, json=[pr_json(4, "milestone-1", "closed")]
+    )
     found = client(handler).find_pull_request("o/r", "milestone-1")
     assert found is not None
     assert found.number == 4
 
 
+def test_find_pull_request_pages_past_the_first_page() -> None:
+    # The match sits on page 2; sampling only the newest page would report
+    # "absent" and licence a duplicate PR.
+    def handler(request: httpx.Request) -> httpx.Response:
+        page = int(request.url.params.get("page", 1))
+        if page == 1:
+            return httpx.Response(
+                200, json=[pr_json(i, f"other-{i}") for i in range(PR_PAGE_SIZE)]
+            )
+        return httpx.Response(200, json=[pr_json(999, "milestone-1", "closed")])
+
+    found = client(handler).find_pull_request("o/r", "milestone-1")
+    assert found is not None
+    assert found.number == 999
+
+
+def test_short_page_ends_the_search_definitively() -> None:
+    calls: list[int] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        calls.append(int(request.url.params.get("page", 1)))
+        return httpx.Response(200, json=[pr_json(1, "other")])
+
+    assert client(handler).find_pull_request("o/r", "milestone-1") is None
+    assert calls == [1]  # one short page proves absence; no further paging
+
+
+def test_unbounded_history_raises_rather_than_guessing() -> None:
+    # Never answer "absent" from an incomplete search: the reconciler turns
+    # this error into "unverifiable" and gates to the human.
+    handler = lambda request: httpx.Response(
+        200, json=[pr_json(i, f"other-{i}") for i in range(PR_PAGE_SIZE)]
+    )
+    with pytest.raises(GiteaError, match="without reaching the end"):
+        client(handler).find_pull_request("o/r", "milestone-1")
+
+
 def test_error_status_raises_gitea_error() -> None:
     handler = lambda request: httpx.Response(403, text="forbidden")
     with pytest.raises(GiteaError, match="403"):
@@ -139,12 +171,7 @@ def test_from_env_requires_config() -> None:
 
 
 def test_reconciler_reports_existing_pr_as_done() -> None:
-    handler = lambda request: httpx.Response(
-        200,
-        json=[pr_json(5, "milestone-1")]
-        if request.url.params.get("state") == "open"
-        else [],
-    )
+    handler = lambda request: httpx.Response(200, json=[pr_json(5, "milestone-1")])
     assert pull_request_reconciler(client(handler), "o/r")(INTENT) is True