test(tbd_ship): cover review-protected + merge-conflict fail-closed paths (#40)

Adds Call-level tests for the two remaining no-merge paths (green CI but the
base requires review, and green CI but the merge returns 409), completing the
acceptance matrix alongside the green/pending/red/no-CI cases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tools/tbd_ship_test.go

@@ -19,12 +19,23 @@ import (
 // shipFake serves the whole tbd_ship flow; runsJSON is the workflow_runs array
 // for the head commit, letting each test drive the CI gate.
 func shipFake(t *testing.T, runsJSON string, merged, deleted *atomic.Bool) *httptest.Server {
+	t.Helper()
+	return shipFakeOpts(t, runsJSON, 0, http.StatusOK, merged, deleted)
+}
+
+// shipFakeOpts adds protection (requiredApprovals>0 → protected) and a merge
+// status code, so tests can drive the review-protected and conflict paths.
+func shipFakeOpts(t *testing.T, runsJSON string, requiredApprovals, mergeStatus int, merged, deleted *atomic.Bool) *httptest.Server {
 	t.Helper()
 	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		p := r.URL.Path
 		w.Header().Set("Content-Type", "application/json")
 		switch {
 		case r.Method == http.MethodGet && strings.Contains(p, "/branch_protections/"):
+			if requiredApprovals > 0 {
+				_, _ = w.Write([]byte(`{"required_approvals":` + itoa(requiredApprovals) + `}`))
+				return
+			}
 			w.WriteHeader(http.StatusNotFound) // unprotected
 			_, _ = w.Write([]byte(`{"message":"not found"}`))
 		case r.Method == http.MethodPost && strings.HasSuffix(p, "/branches"):
@@ -43,7 +54,7 @@ func shipFake(t *testing.T, runsJSON string, merged, deleted *atomic.Bool) *http
 			_, _ = w.Write([]byte(`{"total_count":0,"workflow_runs":` + runsJSON + `}`))
 		case r.Method == http.MethodPost && strings.HasSuffix(p, "/pulls/7/merge"):
 			merged.Store(true)
-			w.WriteHeader(http.StatusOK)
+			w.WriteHeader(mergeStatus)
 			_, _ = w.Write([]byte(`{}`))
 		case r.Method == http.MethodDelete && strings.Contains(p, "/branches/"):
 			deleted.Store(true)
@@ -109,6 +120,36 @@ func TestTBDShip_RedCI_FailsClosed(t *testing.T) {
 	assert.False(t, merged.Load(), "merge must NOT be called when CI is red")
 }
 
+func itoa(n int) string { b, _ := json.Marshal(n); return string(b) }
+
+// Green CI but the base branch requires review → fail closed (no auto-merge).
+func TestTBDShip_ReviewProtected_FailsClosed(t *testing.T) {
+	var merged, deleted atomic.Bool
+	srv := shipFakeOpts(t, `[{"id":1,"status":"completed","conclusion":"success","head_sha":"abc"}]`, 1, http.StatusOK, &merged, &deleted)
+	defer srv.Close()
+
+	res := callShip(t, srv.URL, `{"owner":"mathias","repo":"myrepo","path":"docs/x.md","content":"hi","message":"add x"}`)
+
+	assert.Equal(t, false, res["merged"])
+	assert.NotEmpty(t, res["reason"])
+	assert.Contains(t, res["reason"], "review")
+	assert.False(t, merged.Load(), "must NOT merge a review-protected base")
+}
+
+// Green CI but the merge is unclean (409) → fail closed, PR left open.
+func TestTBDShip_MergeConflict_FailsClosed(t *testing.T) {
+	var merged, deleted atomic.Bool
+	srv := shipFakeOpts(t, `[{"id":1,"status":"completed","conclusion":"success","head_sha":"abc"}]`, 0, http.StatusConflict, &merged, &deleted)
+	defer srv.Close()
+
+	res := callShip(t, srv.URL, `{"owner":"mathias","repo":"myrepo","path":"docs/x.md","content":"hi","message":"add x"}`)
+
+	assert.Equal(t, false, res["merged"])
+	assert.NotEmpty(t, res["reason"])
+	assert.True(t, merged.Load(), "merge is attempted")
+	assert.False(t, deleted.Load(), "branch is NOT deleted on a failed merge")
+}
+
 func TestTBDShip_AllowlistRejects(t *testing.T) {
 	tool := tools.NewTBDShip(gitea.NewClient("http://unused", ""), allowlist.New([]string{"mathias"}))
 	_, err := tool.Call(context.Background(), json.RawMessage(`{"owner":"evil","repo":"r","path":"p","content":"c","message":"m"}`))