fix: address verified gadfly P5 findings (canary robustness)

All 3 cloud models converged (all "minor" — example code, no blocking):
- Consolidate: a model whose every lens errored now reads "review incomplete",
  not a misleading "no issues found" (all 3 models). + test.
- Consolidate: swarm-cancelled (unattributed) cells now surface a "swarm
  cancelled — N cell(s) did not run" banner instead of vanishing (all 3). + test.
- main: io.ReadAll(os.Stdin) error is surfaced (all 3); a TTY stdin no longer
  hangs forever (TTY guard, minimax).
- providerOf: a bare tier name now keys its own PerKey bucket instead of all
  bare tiers collapsing onto "tier" (minimax, glm-5.2) — distinct tiers throttle
  independently.
- Review doc reworded (the closure, not fanout, carries per-cell errors).

Left as documented example-scope behavior: no per-cell timeout (caller supplies
ctx), unknown-severity → lowest rank (no crash).

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

examples/reviewer/reviewer.go

@@ -92,7 +92,7 @@ const baseSystemPrompt = "You are an adversarial code reviewer. Review the diff
 // Review runs every (model × lens) cell of the swarm concurrently, bounded by
 // opts (total + per-provider caps), and returns one LensResult per cell. A cell
 // whose model call fails carries the error in LensResult.Err — one bad cell
-// never aborts the swarm (fanout captures per-item errors).
+// never aborts the swarm (the closure embeds per-cell errors in LensResult.Err).
 func Review(ctx context.Context, models []NamedModel, lenses []Lens, diff string, opts fanout.Options[cell]) []LensResult {
 	cells := make([]cell, 0, len(models)*len(lenses))
 	for _, m := range models {
@@ -139,8 +139,12 @@ type cell struct {
 func Consolidate(results []LensResult) string {
 	byModel := map[string][]LensResult{}
 	var order []string
+	aborted := 0 // cells dropped before running (swarm cancelled) — no model attribution
 	for _, r := range results {
 		if r.Model == "" {
+			if r.Err != nil {
+				aborted++
+			}
 			continue
 		}
 		if _, ok := byModel[r.Model]; !ok {
@@ -151,6 +155,9 @@ func Consolidate(results []LensResult) string {
 	sort.Strings(order)
 
 	var b strings.Builder
+	if aborted > 0 {
+		fmt.Fprintf(&b, "> ⚠ swarm cancelled — %d cell(s) did not run; results below are partial.\n\n", aborted)
+	}
 	for _, m := range order {
 		rs := byModel[m]
 		var all []Finding
@@ -168,10 +175,16 @@ func Consolidate(results []LensResult) string {
 				}
 			}
 		}
+		// A model whose every lens errored produced NO data — saying "no issues
+		// found" would be misleading, so it gets its own verdict.
+		successful := len(rs) - errored
 		verdict := "no issues found"
-		if worst >= severityRank(SevHigh) {
+		switch {
+		case successful == 0 && errored > 0:
+			verdict = "review incomplete"
+		case worst >= severityRank(SevHigh):
 			verdict = "blocking issues found"
-		} else if worst >= 0 {
+		case worst >= 0:
 			verdict = "minor issues"
 		}
 		fmt.Fprintf(&b, "## %s — %s", m, verdict)