watchpr: arm the conflict rule on a new merge computation

A mergeable=false baseline meant a conflict could never be reported, since
Gitea sends false while it recomputes after a push. Arm on a head or base SHA
change as well as on a mergeable poll, break the conflict run on unknown and
failed polls, and print the baseline with the conditions it suppresses.

cmd/watchpr/main.go

@@ -1,8 +1,10 @@
 // Command watchpr polls one or more Gitea pull requests and exits when a
 // tracked PR changes in a way worth alerting on: it merges or closes, gets a
 // new comment from someone other than the agent, its CI fails, or it loses
-// mergeability. Benign transitions (CI pending→success, the agent's own
-// comments) are ignored.
+// mergeability after the baseline. Benign transitions (CI pending→success, the
+// agent's own pushes and comments) are ignored, and so is any condition that was
+// already true at the baseline -- which watchpr prints, so a run started against
+// a conflicted or CI-red PR says so.
 //
 //	watchpr owner/repo#12 owner/repo:15
 //	watchpr --once --json owner/repo#12
@@ -14,6 +16,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"strings"
 	"time"
 
 	"git.unkin.net/unkin/agent-tools/internal/agent"
@@ -43,7 +46,8 @@ func newRootCmd() *cobra.Command {
 		Short: "Poll Gitea PRs and exit when one changes meaningfully.",
 		Long: "watchpr polls each PR every --interval and exits (reporting what changed)\n" +
 			"when a PR merges/closes, gets a new non-agent comment, its CI fails, or it\n" +
-			"loses mergeability. Accepts refs as owner/repo#N or owner/repo:N.",
+			"loses mergeability after the baseline. Conditions already true at the\n" +
+			"baseline are printed, not alerted on. Refs take owner/repo#N or owner/repo:N.",
 		Version:      version,
 		Args:         cobra.ArbitraryArgs,
 		SilenceUsage: true,
@@ -126,9 +130,13 @@ func runWatch(c *agent.GiteaClient, refs []agent.PRRef, interval time.Duration,
 	ticker := time.NewTicker(interval)
 	defer ticker.Stop()
 
-	onBaseline := func() {
-		if !jsonMode {
-			fmt.Fprintf(os.Stderr, "watching %d PR(s) every %s; baseline established\n", len(refs), interval)
+	onBaseline := func(states []agent.PRState) {
+		if jsonMode {
+			return
+		}
+		fmt.Fprintf(os.Stderr, "watching %d PR(s) every %s; baseline established\n", len(refs), interval)
+		for _, st := range states {
+			fmt.Fprintln(os.Stderr, baselineLine(st))
 		}
 	}
 	onError := func(ref agent.PRRef, err error) {
@@ -176,8 +184,36 @@ func report(key, reason string, st agent.PRState, jsonMode bool) {
 }
 
 func printState(st agent.PRState) {
-	fmt.Printf("%s state=%s merged=%t mergeable=%s ci=%s head=%s comments(non-agent)=%d\n",
-		st.Ref.String(), st.State, st.Merged, st.Mergeable, ciOrNone(st.CIStatus), shortSHA(st.HeadSHA), st.NonAgentComments)
+	fmt.Println(stateLine(st))
+}
+
+func stateLine(st agent.PRState) string {
+	return fmt.Sprintf("%s state=%s merged=%t mergeable=%s ci=%s head=%s base=%s comments(non-agent)=%d",
+		st.Ref.String(), st.State, st.Merged, st.Mergeable, ciOrNone(st.CIStatus),
+		shortSHA(st.HeadSHA), shortSHA(st.BaseSHA), st.NonAgentComments)
+}
+
+// baselineLine describes the state a watch started from, naming the conditions
+// it will deliberately stay silent about: watchpr alerts on changes, so a PR
+// that is already conflicted or already CI-red produces no alert for either, and
+// that suppression has to be visible to whoever started the watch.
+func baselineLine(st agent.PRState) string {
+	line := "  baseline " + stateLine(st)
+	if s := suppressedAtBaseline(st); s != "" {
+		return line + " -- " + s + "; not alerting on a pre-existing condition"
+	}
+	return line
+}
+
+func suppressedAtBaseline(st agent.PRState) string {
+	var conds []string
+	if st.Mergeable == agent.MergeNo {
+		conds = append(conds, "already non-mergeable (a real conflict, or Gitea still recomputing)")
+	}
+	if st.CIStatus == "failure" || st.CIStatus == "error" {
+		conds = append(conds, "CI already "+st.CIStatus)
+	}
+	return strings.Join(conds, ", ")
 }
 
 func ciOrNone(s string) string {

cmd/watchpr/main_test.go

@@ -182,3 +182,33 @@ func TestDescribeFailureNamesTheCause(t *testing.T) {
 		})
 	}
 }
+
+// A watch started against an already conflicted or CI-red PR sends no alert for
+// either, so the baseline line has to say that is what it is doing: before this,
+// such a run printed nothing in either direction.
+func TestBaselineLineNamesSuppressedConditions(t *testing.T) {
+	st := agent.PRState{
+		Ref:       agent.PRRef{Owner: "unkin", Repo: "repo", Number: 7},
+		State:     "open",
+		Mergeable: agent.MergeNo,
+		CIStatus:  "failure",
+		HeadSHA:   "cafebabecafebabe",
+		BaseSHA:   "deadbeefdeadbeef",
+	}
+	got := baselineLine(st)
+	for _, want := range []string{
+		"unkin/repo#7", "mergeable=false", "ci=failure", "head=cafebabe", "base=deadbeef",
+		"already non-mergeable", "CI already failure", "not alerting",
+	} {
+		if !strings.Contains(got, want) {
+			t.Errorf("baselineLine = %q, want it to mention %q", got, want)
+		}
+	}
+
+	clean := st
+	clean.Mergeable = agent.MergeYes
+	clean.CIStatus = "success"
+	if got := baselineLine(clean); strings.Contains(got, "not alerting") {
+		t.Errorf("baselineLine = %q, want no suppression note for a clean baseline", got)
+	}
+}

internal/agent/gitea.go

@@ -200,6 +200,11 @@ type PullRequest struct {
 		Ref   string `json:"ref"`
 		Label string `json:"label"`
 	} `json:"head"`
+	// Base.Sha is the base branch tip as of this response, not the merge base
+	// recorded when the PR was opened.
+	Base struct {
+		Sha string `json:"sha"`
+	} `json:"base"`
 }
 
 // prPageSize is the per-page limit for the pulls listing; maxPRPages caps how

internal/agent/watch.go

@@ -17,9 +17,11 @@ func IsPRGone(err error) bool {
 	return errors.Is(err, errPRGone)
 }
 
-// Mergeability is Gitea's mergeable flag as a tri-state. The flag is null or
-// absent while Gitea recomputes the merge base, and an unknown value must not be
-// read as either answer.
+// Mergeability is Gitea's mergeable flag. Gitea 1.26 always sends a plain bool,
+// and sends false both for a real conflict and while it recomputes the merge
+// base after a push, so false on its own decides nothing (prWatch resolves it).
+// Unknown covers what the bool cannot carry: an absent or null flag from another
+// Gitea build, and a snapshot no successful poll ever filled in.
 type Mergeability int
 
 const (
@@ -68,6 +70,7 @@ type PRState struct {
 	State            string       `json:"state"` // open / closed
 	Merged           bool         `json:"merged"`
 	HeadSHA          string       `json:"head_sha"`
+	BaseSHA          string       `json:"base_sha"`
 	Mergeable        Mergeability `json:"mergeable"`
 	CIStatus         string       `json:"ci_status"` // success / pending / failure / error / ""
 	NonAgentComments int          `json:"non_agent_comments"`
@@ -101,6 +104,7 @@ func FetchState(c *GiteaClient, ref PRRef, agentLogin string) (PRState, error) {
 		State:            pr.State,
 		Merged:           pr.Merged,
 		HeadSHA:          pr.Head.Sha,
+		BaseSHA:          pr.Base.Sha,
 		Mergeable:        pr.Mergeable,
 		CIStatus:         ci,
 		NonAgentComments: countNonAgentComments(comments, agentLogin),
@@ -141,48 +145,67 @@ func terminalState(st PRState) (bool, string) {
 	return false, ""
 }
 
-// conflictPolls is how many consecutive non-mergeable polls confirm a real
-// conflict. Gitea reports mergeable=false while it recomputes the merge base
-// after a push, so a single poll is debounced.
+// conflictPolls is how many consecutive non-mergeable polls of an unchanged
+// merge computation confirm a real conflict.
 const conflictPolls = 2
 
-// prWatch tracks one PR across polls. Mergeability needs more memory than the
-// previous snapshot: losing it only counts as a change if the PR was mergeable
-// at some point after watching began, since a conflict that predates the
-// baseline is the state the operator is already waiting on.
+// prWatch tracks one PR across polls, because mergeability needs more memory
+// than the previous snapshot. Gitea reports mergeable=false while it recomputes
+// the merge base after a push, so a false is only trusted once this watch has
+// seen a merge computation start: the PR was mergeable at some point, or its
+// head or base SHA moved. A bare false inherited from the baseline says nothing
+// -- it is equally a conflict the operator is already waiting on and a recompute
+// in flight -- so it arms nothing.
 type prWatch struct {
-	prev          PRState
-	everMergeable bool
-	conflicts     int
+	prev      PRState
+	armed     bool
+	conflicts int
 }
 
 func newPRWatch(baseline PRState) *prWatch {
-	w := &prWatch{prev: baseline}
-	w.track(baseline)
-	return w
+	return &prWatch{prev: baseline, armed: baseline.Mergeable == MergeYes}
 }
 
-// track folds one snapshot's mergeability into the run of observations. Unknown
-// neither confirms a conflict nor clears one.
+// mergeInputsChanged reports whether the commits Gitea merges have moved, which
+// starts a fresh merge computation whose result is attributable to this watch.
+func mergeInputsChanged(prev, cur PRState) bool {
+	return cur.HeadSHA != prev.HeadSHA || cur.BaseSHA != prev.BaseSHA
+}
+
+// track folds one snapshot's mergeability into the run of observations. The
+// polls that confirm a conflict must be adjacent, so anything but another
+// non-mergeable observation breaks the run.
 func (w *prWatch) track(st PRState) {
 	switch st.Mergeable {
-	case MergeYes:
-		w.everMergeable = true
-		w.conflicts = 0
 	case MergeNo:
 		w.conflicts++
+	case MergeYes:
+		w.armed = true
+		w.conflicts = 0
+	default:
+		w.conflicts = 0
 	}
 }
 
+// missed records a poll that never produced a snapshot; the run of adjacent
+// non-mergeable observations does not survive the gap.
+func (w *prWatch) missed() {
+	w.conflicts = 0
+}
+
 // observe folds in the newest snapshot and reports whether the watch should end.
 func (w *prWatch) observe(cur PRState) (bool, string) {
 	changed, reason := MeaningfulChange(w.prev, cur)
+	if mergeInputsChanged(w.prev, cur) {
+		w.armed = true
+		w.conflicts = 0
+	}
 	w.prev = cur
 	w.track(cur)
 	if changed {
 		return true, reason
 	}
-	if w.everMergeable && w.conflicts >= conflictPolls && cur.State == "open" {
+	if w.armed && w.conflicts >= conflictPolls && cur.State == "open" {
 		return true, "PR lost mergeability (conflict)"
 	}
 	return false, ""
@@ -202,10 +225,11 @@ const MaxPollFailures = 20
 // is gone, renamed, or no longer visible), and MaxPollFailures consecutive
 // failures of one PR all abort, because a watcher that sees nothing must not
 // look healthy.
-// onBaseline, if set, fires once after all baselines are captured and before the
-// first tick.
-func Watch(f StateFetcher, refs []PRRef, agentLogin string, ticks <-chan time.Time, onBaseline func(), onError func(PRRef, error)) (WatchResult, error) {
+// onBaseline, if set, receives every captured baseline once, before the first
+// tick, so a caller can show what state the watch started from.
+func Watch(f StateFetcher, refs []PRRef, agentLogin string, ticks <-chan time.Time, onBaseline func([]PRState), onError func(PRRef, error)) (WatchResult, error) {
 	watches := make(map[string]*prWatch, len(refs))
+	baselines := make([]PRState, 0, len(refs))
 	for _, ref := range refs {
 		st, err := f.FetchState(ref, agentLogin)
 		if err != nil {
@@ -215,9 +239,10 @@ func Watch(f StateFetcher, refs []PRRef, agentLogin string, ticks <-chan time.Ti
 			return WatchResult{Ref: ref, Reason: reason, State: st}, nil
 		}
 		watches[ref.String()] = newPRWatch(st)
+		baselines = append(baselines, st)
 	}
 	if onBaseline != nil {
-		onBaseline()
+		onBaseline(baselines)
 	}
 	fails := make(map[string]int, len(refs))
 	for range ticks {
@@ -229,6 +254,7 @@ func Watch(f StateFetcher, refs []PRRef, agentLogin string, ticks <-chan time.Ti
 					return WatchResult{}, fmt.Errorf("polling %s: %w", key, err)
 				}
 				fails[key]++
+				watches[key].missed()
 				if onError != nil {
 					onError(ref, err)
 				}
@@ -265,8 +291,8 @@ func isFailedCI(state string) bool {
 // MeaningfulChange compares a previous state to the current one and reports
 // whether a change warrants alerting the operator, with a human-readable
 // reason. Benign transitions (CI pending→success, the agent's own comments, a
-// new head commit, an unchanged snapshot) return false. Mergeability is not
-// decided here: it takes a whole run of observations, which prWatch keeps.
+// new head or base commit, an unchanged snapshot) return false. Mergeability is
+// not decided here: it takes a whole run of observations, which prWatch keeps.
 //
 // Alerting conditions:
 //   - the PR merged

internal/agent/watch_test.go

@@ -18,6 +18,7 @@ func base() PRState {
 		State:            "open",
 		Merged:           false,
 		HeadSHA:          "abc123",
+		BaseSHA:          "base000",
 		Mergeable:        MergeYes,
 		CIStatus:         "pending",
 		NonAgentComments: 0,
@@ -209,16 +210,16 @@ func TestWatchDetectsMergeAfterBaseline(t *testing.T) {
 	merged.Merged = true
 	f := &fakeFetcher{states: []PRState{open, merged}} // baseline open, then merged
 
-	baselineFired := false
+	var baselines []PRState
 	ticks := make(chan time.Time, 1)
 	ticks <- time.Now()
 	res, err := Watch(f, []PRRef{open.Ref}, "unkin-agent",
-		ticks, func() { baselineFired = true }, nil)
+		ticks, func(sts []PRState) { baselines = sts }, nil)
 	if err != nil {
 		t.Fatalf("Watch: %v", err)
 	}
-	if !baselineFired {
-		t.Errorf("onBaseline should fire for an open baseline")
+	if len(baselines) != 1 || baselines[0].Ref != open.Ref {
+		t.Errorf("onBaseline received %v, want the one open baseline", baselines)
 	}
 	if res.Reason != "PR merged" {
 		t.Errorf("reason = %q, want %q", res.Reason, "PR merged")
@@ -903,7 +904,8 @@ func TestPRWatchMergeability(t *testing.T) {
 		{"unknown at baseline does not arm the rule", MergeUnknown, []Mergeability{MergeNo, MergeNo, MergeNo}, 0},
 		{"unknown at baseline then a real loss alerts", MergeUnknown, []Mergeability{MergeYes, MergeNo, MergeNo}, 3},
 		{"a baseline conflict resolved then lost again alerts", MergeNo, []Mergeability{MergeYes, MergeNo, MergeNo}, 3},
-		{"unknown between conflicted polls does not clear them", MergeYes, []Mergeability{MergeNo, MergeUnknown, MergeNo}, 3},
+		{"unknown between conflicted polls breaks the run", MergeYes, []Mergeability{MergeNo, MergeUnknown, MergeNo}, 0},
+		{"the run restarts after an unknown", MergeYes, []Mergeability{MergeNo, MergeUnknown, MergeNo, MergeNo}, 4},
 		{"unknown alone is never a conflict", MergeYes, []Mergeability{MergeUnknown, MergeUnknown, MergeUnknown}, 0},
 	}
 	for _, tt := range tests {
@@ -928,8 +930,9 @@ func TestPRWatchMergeability(t *testing.T) {
 	}
 }
 
-// An absent or null mergeable flag means Gitea has not computed it yet, and must
-// decode as unknown rather than as a conflict.
+// Gitea 1.26 always sends mergeable as a plain bool, so unknown is reserved for
+// what that bool cannot carry: an absent or null flag must decode as unknown
+// rather than as a conflict, and unknown must encode back as null.
 func TestMergeabilityDecoding(t *testing.T) {
 	tests := map[string]Mergeability{
 		`{"number":7}`:                   MergeUnknown,
@@ -954,3 +957,206 @@ func TestMergeabilityDecoding(t *testing.T) {
 		t.Errorf("unknown mergeability encoded as %s, want null", out)
 	}
 }
+
+// The inverse of the bug this PR fixed: Gitea reports mergeable=false while it
+// recomputes the merge base after a push, and watchpr is normally started right
+// after the agent pushes, so the baseline can land inside that window. Demanding
+// a mergeable observation to arm the rule left a genuinely conflicted PR silent
+// forever. The new head is a new merge computation, so the conflict it confirms
+// belongs to this watch.
+func TestWatchAlertsWhenBaselineLandedInTheRecomputeWindow(t *testing.T) {
+	baseline := base()
+	baseline.Mergeable = MergeNo // still recomputing; the push is not visible yet
+
+	pushed := base()
+	pushed.Mergeable = MergeNo
+	pushed.HeadSHA = "def456"
+
+	f := &fakeFetcher{states: []PRState{baseline, pushed, pushed, pushed}}
+	res, err := Watch(f, []PRRef{baseline.Ref}, "unkin-agent", drainableTicks(3), nil, nil)
+	if err != nil {
+		t.Fatalf("Watch: %v", err)
+	}
+	if res.Reason != "PR lost mergeability (conflict)" {
+		t.Fatalf("reason = %q, want the mergeability loss; a conflict must not be unreportable because the baseline caught the recompute", res.Reason)
+	}
+	if f.calls != 3 {
+		t.Errorf("fetch calls = %d, want 3 (baseline + the two conflicted polls on the new head)", f.calls)
+	}
+}
+
+// A base-branch move restarts the same merge computation, so a conflict that
+// only becomes visible once someone merges into main alerts too.
+func TestWatchAlertsWhenBaseMovedIntoAConflict(t *testing.T) {
+	baseline := base()
+	baseline.Mergeable = MergeNo
+
+	moved := base()
+	moved.Mergeable = MergeNo
+	moved.BaseSHA = "base111"
+
+	f := &fakeFetcher{states: []PRState{baseline, moved, moved}}
+	res, err := Watch(f, []PRRef{baseline.Ref}, "unkin-agent", drainableTicks(3), nil, nil)
+	if err != nil {
+		t.Fatalf("Watch: %v", err)
+	}
+	if res.Reason != "PR lost mergeability (conflict)" {
+		t.Errorf("reason = %q, want the mergeability loss", res.Reason)
+	}
+}
+
+// The fix this PR exists for: a conflict predating the watch, on a head and base
+// that never move, is the condition the operator is already waiting on and must
+// stay silent however long the watch runs.
+func TestWatchNeverAlertsOnAStableBaselineConflict(t *testing.T) {
+	stuck := base()
+	stuck.Mergeable = MergeNo
+	f := &fakeFetcher{states: []PRState{stuck}}
+
+	res, err := Watch(f, []PRRef{stuck.Ref}, "unkin-agent", drainableTicks(100), nil, nil)
+	if err != nil {
+		t.Fatalf("Watch: %v", err)
+	}
+	if res.Reason != "" {
+		t.Fatalf("Watch ended with %q after 100 unchanged polls; a conflict that predates the watch is not a change", res.Reason)
+	}
+}
+
+// Head and base movement arm the conflict rule but are not themselves alerts: a
+// push, or a base that moves under the PR, must not end a watch.
+func TestWatchArmingMovementDoesNotAlert(t *testing.T) {
+	start := base()
+	pushed := base()
+	pushed.HeadSHA = "def456"
+	rebased := base()
+	rebased.HeadSHA = "789abc"
+	rebased.BaseSHA = "base111"
+	f := &fakeFetcher{states: []PRState{start, pushed, rebased}}
+
+	res, err := Watch(f, []PRRef{start.Ref}, "unkin-agent", drainableTicks(5), nil, nil)
+	if err != nil {
+		t.Fatalf("Watch: %v", err)
+	}
+	if res.Reason != "" {
+		t.Fatalf("Watch ended with %q; a new head or base is not a change worth alerting on", res.Reason)
+	}
+}
+
+// The polls that confirm a conflict must be adjacent. A failed poll produces no
+// snapshot, so the run cannot span it and two non-adjacent falses do not fire.
+func TestWatchConflictRunDoesNotSpanAFailedPoll(t *testing.T) {
+	ok := base()
+	conflicted := base()
+	conflicted.Mergeable = MergeNo
+	f := &fakeFetcher{
+		states: []PRState{ok, conflicted, conflicted, conflicted, conflicted},
+		errs:   []error{nil, nil, errors.New("HTTP 502"), nil, nil},
+	}
+
+	res, err := Watch(f, []PRRef{ok.Ref}, "unkin-agent", drainableTicks(4), nil, func(PRRef, error) {})
+	if err != nil {
+		t.Fatalf("Watch: %v", err)
+	}
+	if res.Reason != "PR lost mergeability (conflict)" {
+		t.Fatalf("reason = %q, want the mergeability loss on the two adjacent polls", res.Reason)
+	}
+	if f.calls != 5 {
+		t.Errorf("fetch calls = %d, want 5: the falses either side of the failed poll are not a run", f.calls)
+	}
+}
+
+// perRefFetcher scripts a separate sequence per ref, so a multi-ref watch can be
+// driven with each PR doing something different.
+type perRefFetcher struct {
+	states map[string][]PRState
+	calls  map[string]int
+}
+
+func (f *perRefFetcher) FetchState(ref PRRef, _ string) (PRState, error) {
+	key := ref.String()
+	seq := f.states[key]
+	i := f.calls[key]
+	if i >= len(seq) {
+		i = len(seq) - 1
+	}
+	f.calls[key]++
+	return seq[i], nil
+}
+
+// Each ref keeps its own run of observations: one PR's mergeability, pushes and
+// resolutions must neither arm nor disarm another's conflict rule.
+func TestWatchTracksRefsIndependently(t *testing.T) {
+	refA := PRRef{Owner: "unkin", Repo: "repo", Number: 1}
+	refB := PRRef{Owner: "unkin", Repo: "repo", Number: 2}
+	snap := func(ref PRRef, m Mergeability, head string) PRState {
+		s := base()
+		s.Ref = ref
+		s.Mergeable = m
+		s.HeadSHA = head
+		return s
+	}
+
+	tests := []struct {
+		name string
+		a, b []PRState
+		want string // reason, "" for no alert
+	}{
+		{
+			name: "a mergeable neighbour does not arm a baseline conflict",
+			a:    []PRState{snap(refA, MergeYes, "aaa")},
+			b:    []PRState{snap(refB, MergeNo, "bbb")},
+			want: "",
+		},
+		{
+			name: "a neighbour's push does not arm a baseline conflict",
+			a:    []PRState{snap(refA, MergeYes, "aaa"), snap(refA, MergeYes, "aa2"), snap(refA, MergeYes, "aa3")},
+			b:    []PRState{snap(refB, MergeNo, "bbb")},
+			want: "",
+		},
+		{
+			name: "a neighbour's mergeable polls do not clear another's run",
+			a:    []PRState{snap(refA, MergeYes, "aaa")},
+			b:    []PRState{snap(refB, MergeYes, "bbb"), snap(refB, MergeNo, "bbb"), snap(refB, MergeNo, "bbb")},
+			want: "PR lost mergeability (conflict)",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			f := &perRefFetcher{
+				states: map[string][]PRState{refA.String(): tt.a, refB.String(): tt.b},
+				calls:  map[string]int{},
+			}
+			res, err := Watch(f, []PRRef{refA, refB}, "unkin-agent", drainableTicks(6), nil, nil)
+			if err != nil {
+				t.Fatalf("Watch: %v", err)
+			}
+			if res.Reason != tt.want {
+				t.Fatalf("reason = %q, want %q", res.Reason, tt.want)
+			}
+			if tt.want != "" && res.Ref != refB {
+				t.Errorf("alert names %s, want %s", res.Ref, refB)
+			}
+		})
+	}
+}
+
+// A watch that will deliberately stay silent about a pre-existing conflict has
+// to hand its caller the baseline it is staying silent about.
+func TestWatchReportsBaselineStates(t *testing.T) {
+	stuck := base()
+	stuck.Mergeable = MergeNo
+	stuck.CIStatus = "failure"
+	f := &fakeFetcher{states: []PRState{stuck}}
+
+	var got []PRState
+	if _, err := Watch(f, []PRRef{stuck.Ref}, "unkin-agent", drainableTicks(1),
+		func(sts []PRState) { got = sts }, nil); err != nil {
+		t.Fatalf("Watch: %v", err)
+	}
+	if len(got) != 1 {
+		t.Fatalf("onBaseline received %d state(s), want 1", len(got))
+	}
+	if got[0].Mergeable != MergeNo || got[0].CIStatus != "failure" {
+		t.Errorf("baseline = %+v, want the conflicted, CI-red snapshot the watch started from", got[0])
+	}
+}