🐛 automerge: contributor lane treats incomplete file list as a standing skip

changelog.d/fixed-18121-contributor-lane-incomplete-files.md

@@ -0,0 +1 @@
+- The contributor-lane automerge sweep now treats a PR with more changed files than GitHub's files API returns (3000) as a standing `files-evidence` skip instead of re-warning every sweep.

src/pkg/github/automerge/automerge_contributor_lane.go

@@ -1405,6 +1405,13 @@ func (c *Engine) evaluateContributorLanePR(ctx context.Context, displayRepo, own
 		c.info("contributor-lane admitted", "repo", displayRepo, "pr", number, "author", author, "reason", "contributor-lane:auto-promoted", "merged_prs", claim.AutoPromoted, "scope", contributorAutoPromotionScopeName(claim.AutoPromotedHiveWide), "repos", claim.AutoPromotedRepos)
 	}
 	files, err := ListChangedFiles(caller, c.gh, owner, repo, pr)
+	if errors.Is(err, hgithub.ErrIncompletePRFileList) {
+		// More changed files than GitHub's files API will ever return: the
+		// diff fences cannot be read on any tick, so this is a standing
+		// verdict (fail closed, nil error) like adoptionDiffRefusal's, not a
+		// transient fault re-WARNed every sweep (hivecommons/hive#18121).
+		return eval, contributorLaneReasonFilesEvidence, nil
+	}
 	if err != nil {
 		return eval, contributorLaneReasonFilesEvidence, err
 	}

src/pkg/github/automerge/automerge_contributor_lane_test.go

@@ -60,6 +60,7 @@ type contributorLaneFixture struct {
 	omitAssociation bool
 	files           []map[string]any
 	filesStatus     int
+	changedFiles    int // changed_files on the PR payload; 0 omits it
 	listStatus      int
 	getStatus       int
 	recheckHeadSHA  string
@@ -219,6 +220,9 @@ func newContributorLaneAPI(t *testing.T, fx *contributorLaneFixture) *httptest.S
 			if !fx.omitAssociation {
 				p["author_association"] = association
 			}
+			if fx.changedFiles != 0 {
+				p["changed_files"] = fx.changedFiles
+			}
 			if fx.headCommittedAt != "" {
 				p["updated_at"] = fx.headCommittedAt
 			}
@@ -760,6 +764,9 @@ func TestTrySweepContributorLanePRSkipReasons(t *testing.T) {
 			wantMerges: 1,
 		},
 		{name: "files fetch error", mutate: func(fx *contributorLaneFixture) { fx.filesStatus = http.StatusInternalServerError }, wantReason: contributorLaneReasonFilesEvidence, wantErr: true},
+		// More changed files than the files API returns is a standing
+		// verdict, not a transient error re-WARNed every sweep (#18121).
+		{name: "incomplete files list", mutate: func(fx *contributorLaneFixture) { fx.changedFiles = 5204 }, wantReason: contributorLaneReasonFilesEvidence},
 		{name: "claim comments fetch error", mutate: func(fx *contributorLaneFixture) { fx.issueCommentsSt = http.StatusInternalServerError }, wantReason: "claim-comments-fetch", wantErr: true},
 		{
 			name: "reporter-trust hold",

src/pkg/github/automerge/automerge_relay_gate_test.go

@@ -251,6 +251,15 @@ func TestRelayMergeRefusalFailsClosed(t *testing.T) {
 			t.Fatalf("err = %v, want lane evidence error", err)
 		}
 	})
+	t.Run("incomplete files list refuses", func(t *testing.T) {
+		fx := validContributorFixture()
+		fx.changedFiles = 5204
+		engine, _ := relayGateEngine(t, &fx, defaultContributorLanePolicy(), Options{})
+		refusal, err := engine.RelayMergeRefusal(context.Background(), "widget", 7, "sha7")
+		if err != nil || !strings.Contains(refusal, contributorLaneReasonFilesEvidence) {
+			t.Fatalf("refusal=%q err=%v, want standing files-evidence refusal", refusal, err)
+		}
+	})
 }
 
 func TestRelayMergeRefusalText(t *testing.T) {