diff --git a/agents.go b/agents.go
index 09cf390..57e88ba 100644
--- a/agents.go
+++ b/agents.go
@@ -14,20 +14,17 @@ type Agent struct {
 	Notes    string `yaml:"notes,omitempty"`
 }
 
-type Config struct {
-	Agents []Agent `yaml:"agents"`
-}
-
 func loadAgents(path string) ([]Agent, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
 		return nil, err
 	}
-	var cfg Config
+	var cfg struct {
+		Agents []Agent `yaml:"agents"`
+	}
 	if err := yaml.Unmarshal(data, &cfg); err != nil {
 		return nil, err
 	}
-	// validate each entry has owner + repo
 	for i, a := range cfg.Agents {
 		if a.Owner == "" || a.Repo == "" {
 			return nil, fmt.Errorf("entry %d missing owner or repo", i)
diff --git a/agents_test.go b/agents_test.go
new file mode 100644
index 0000000..94b9b61
--- /dev/null
+++ b/agents_test.go
@@ -0,0 +1,162 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestLoadAgents_ValidationErrors(t *testing.T) {
+	tests := []struct {
+		name      string
+		yaml      string
+		expectErr bool
+		errSubstr string
+		desc      string
+	}{
+		{
+			name: "valid entry",
+			yaml: `agents:
+  - owner: org
+    repo: repo1
+    category: tools
+`,
+			expectErr: false,
+			desc:      "should load valid entry",
+		},
+		{
+			name: "missing owner",
+			yaml: `agents:
+  - repo: repo1
+`,
+			expectErr: true,
+			errSubstr: "entry 0 missing owner or repo",
+			desc:      "should fail on missing owner",
+		},
+		{
+			name: "missing repo",
+			yaml: `agents:
+  - owner: org
+`,
+			expectErr: true,
+			errSubstr: "entry 0 missing owner or repo",
+			desc:      "should fail on missing repo",
+		},
+		{
+			name: "empty owner",
+			yaml: `agents:
+  - owner: ""
+    repo: repo1
+`,
+			expectErr: true,
+			errSubstr: "entry 0 missing owner or repo",
+			desc:      "should fail on empty owner",
+		},
+		{
+			name: "empty repo",
+			yaml: `agents:
+  - owner: org
+    repo: ""
+`,
+			expectErr: true,
+			errSubstr: "entry 0 missing owner or repo",
+			desc:      "should fail on empty repo",
+		},
+		{
+			name: "valid multiple entries",
+			yaml: `agents:
+  - owner: org1
+    repo: repo1
+  - owner: org2
+    repo: repo2
+    category: ai
+`,
+			expectErr: false,
+			desc:      "should load multiple valid entries",
+		},
+		{
+			name: "second entry missing owner",
+			yaml: `agents:
+  - owner: org1
+    repo: repo1
+  - repo: repo2
+`,
+			expectErr: true,
+			errSubstr: "entry 1 missing owner or repo",
+			desc:      "should report correct index for failing entry",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tmpDir := t.TempDir()
+			tmpFile := tmpDir + "/agents.yml"
+
+			if err := os.WriteFile(tmpFile, []byte(tt.yaml), 0600); err != nil {
+				t.Fatalf("WriteFile failed: %v", err)
+			}
+
+			agents, err := loadAgents(tmpFile)
+
+			if tt.expectErr {
+				if err == nil {
+					t.Errorf("%s: expected error, got nil", tt.desc)
+				} else if !strings.Contains(err.Error(), tt.errSubstr) {
+					t.Errorf("%s: expected error containing %q, got %q", tt.desc, tt.errSubstr, err.Error())
+				}
+				if agents != nil {
+					t.Errorf("%s: expected nil agents on error, got %v", tt.desc, agents)
+				}
+			} else {
+				if err != nil {
+					t.Errorf("%s: expected no error, got %v", tt.desc, err)
+				}
+				if agents == nil {
+					t.Errorf("%s: expected non-nil agents", tt.desc)
+				}
+			}
+		})
+	}
+}
+
+func TestLoadAgents_EmptyList(t *testing.T) {
+	// Empty agents list should load successfully (edge case).
+	tmpDir := t.TempDir()
+	tmpFile := tmpDir + "/agents.yml"
+
+	yaml := `agents: []`
+	if err := os.WriteFile(tmpFile, []byte(yaml), 0600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	agents, err := loadAgents(tmpFile)
+	if err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+	if agents == nil || len(agents) != 0 {
+		t.Errorf("expected empty agents slice, got %v", agents)
+	}
+}
+
+func TestLoadAgents_MalformedYAML(t *testing.T) {
+	// Malformed YAML should return a parse error.
+	tmpDir := t.TempDir()
+	tmpFile := tmpDir + "/agents.yml"
+
+	yaml := `agents:
+  - owner: org
+    repo: repo1
+  - this is not valid yaml: {`
+
+	if err := os.WriteFile(tmpFile, []byte(yaml), 0600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	agents, err := loadAgents(tmpFile)
+	if err == nil {
+		t.Errorf("expected error on malformed YAML, got nil")
+	}
+	if agents != nil {
+		t.Errorf("expected nil agents on parse error, got %v", agents)
+	}
+}
diff --git a/github.go b/github.go
index 896aff5..70f749e 100644
--- a/github.go
+++ b/github.go
@@ -5,14 +5,16 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
-	"os"
 	"sort"
 	"strings"
 	"time"
 )
 
 type Stat struct {
+	// CanonicalKey is owner/repo from agents.yml — stable across renames.
+	CanonicalKey  string
 	Owner         string
 	Repo          string
 	Category      string
@@ -53,62 +55,53 @@ const repoFields = `
 		nameWithOwner
 	`
 
+// httpClient has a timeout to prevent hung workflow jobs.
+var httpClient = &http.Client{Timeout: 30 * time.Second}
+
+// chunkSize is the max aliases per GraphQL request (GitHub node-limit safety margin).
+const chunkSize = 50
+
+// maxRetries and retry backoff for transient HTTP/network errors.
+const maxRetries = 3
+
+var retryBackoff = []time.Duration{2 * time.Second, 4 * time.Second, 8 * time.Second}
+
+// fetchStats queries GitHub GraphQL in chunks of up to chunkSize repos per
+// request. Returns an error if any GraphQL errors are present OR if any
+// requested repo is missing from the response — better to fail loud than
+// silently publish a shorter README.
 func fetchStats(token string, agents []Agent) ([]Stat, error) {
-	var b strings.Builder
-	b.WriteString("query {\n")
-	for i, a := range agents {
-		fmt.Fprintf(&b, "  r%d: repository(owner: %q, name: %q) {%s}\n", i, a.Owner, a.Repo, repoFields)
-	}
-	b.WriteString("}\n")
+	collected := make(map[string]*repoNode, len(agents))
 
-	body, err := json.Marshal(map[string]string{"query": b.String()})
-	if err != nil {
-		return nil, err
-	}
+	for start := 0; start < len(agents); start += chunkSize {
+		end := start + chunkSize
+		if end > len(agents) {
+			end = len(agents)
+		}
+		chunk := agents[start:end]
 
-	req, err := http.NewRequest("POST", "https://api.github.com/graphql", bytes.NewReader(body))
-	if err != nil {
-		return nil, err
-	}
-	req.Header.Set("Authorization", "Bearer "+token)
-	req.Header.Set("Content-Type", "application/json")
-	req.Header.Set("User-Agent", "awesome-coding-agents-updater")
-
-	resp, err := http.DefaultClient.Do(req)
-	if err != nil {
-		return nil, err
-	}
-	defer resp.Body.Close()
-
-	raw, err := io.ReadAll(resp.Body)
-	if err != nil {
-		return nil, err
-	}
-	if resp.StatusCode != http.StatusOK {
-		return nil, fmt.Errorf("graphql HTTP %d: %s", resp.StatusCode, raw)
-	}
-
-	var out graphQLResponse
-	if err := json.Unmarshal(raw, &out); err != nil {
-		return nil, fmt.Errorf("decode response: %w (body=%s)", err, raw)
-	}
-	for _, e := range out.Errors {
-		// repos that 404 or are renamed land here; continue with partial data
-		fmt.Fprintf(os.Stderr, "graphql warn: %s (path=%v)\n", e.Message, e.Path)
+		nodes, err := fetchChunk(token, chunk, start)
+		if err != nil {
+			return nil, err
+		}
+		for k, v := range nodes {
+			collected[k] = v
+		}
 	}
 
 	stats := make([]Stat, 0, len(agents))
 	for i, a := range agents {
-		node := out.Data[fmt.Sprintf("r%d", i)]
+		alias := fmt.Sprintf("r%d", i)
+		node := collected[alias]
 		if node == nil {
-			fmt.Fprintf(os.Stderr, "skip %s/%s — no data\n", a.Owner, a.Repo)
-			continue
+			return nil, fmt.Errorf("repo %s/%s missing from GraphQL response", a.Owner, a.Repo)
 		}
 		lang := ""
 		if node.PrimaryLanguage != nil {
 			lang = node.PrimaryLanguage.Name
 		}
 		stats = append(stats, Stat{
+			CanonicalKey:  a.Owner + "/" + a.Repo,
 			Owner:         a.Owner,
 			Repo:          a.Repo,
 			Category:      a.Category,
@@ -121,11 +114,102 @@ func fetchStats(token string, agents []Agent) ([]Stat, error) {
 			NameWithOwner: node.NameWithOwner,
 		})
 	}
+
+	// Sort by stars descending. Ties are ordered by CanonicalKey for determinism
+	// regardless of map-iteration or agents.yml order.
+	sort.Slice(stats, func(i, j int) bool {
+		if stats[i].Stars != stats[j].Stars {
+			return stats[i].Stars > stats[j].Stars
+		}
+		return stats[i].CanonicalKey < stats[j].CanonicalKey
+	})
+
 	return stats, nil
 }
 
-func sortByStars(stats []Stat) {
-	sort.SliceStable(stats, func(i, j int) bool {
-		return stats[i].Stars > stats[j].Stars
-	})
+// fetchChunk sends one GraphQL request for a slice of agents. aliasOffset
+// ensures alias names (r0, r1, …) are globally unique across chunks.
+func fetchChunk(token string, agents []Agent, aliasOffset int) (map[string]*repoNode, error) {
+	var b strings.Builder
+	b.WriteString("query {\n")
+	for i, a := range agents {
+		fmt.Fprintf(&b, "  r%d: repository(owner: %q, name: %q) {%s}\n", aliasOffset+i, a.Owner, a.Repo, repoFields)
+	}
+	b.WriteString("}\n")
+
+	body, err := json.Marshal(map[string]string{"query": b.String()})
+	if err != nil {
+		return nil, err
+	}
+
+	raw, statusCode, err := doWithRetry(token, body)
+	if err != nil {
+		return nil, err
+	}
+	if statusCode != http.StatusOK {
+		return nil, fmt.Errorf("graphql HTTP %d: %s", statusCode, raw)
+	}
+
+	var out graphQLResponse
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return nil, fmt.Errorf("decode response: %w (body=%s)", err, raw)
+	}
+
+	// Treat any GraphQL-level error as fatal — partial data silently shrinks
+	// the README and corrupts future delta math.
+	if len(out.Errors) > 0 {
+		msgs := make([]string, len(out.Errors))
+		for i, e := range out.Errors {
+			msgs[i] = fmt.Sprintf("%s (path=%v)", e.Message, e.Path)
+		}
+		return nil, fmt.Errorf("graphql errors: %s", strings.Join(msgs, "; "))
+	}
+
+	return out.Data, nil
+}
+
+// doWithRetry executes the GraphQL POST with exponential backoff on transient
+// errors (network failures, HTTP 5xx, HTTP 429). 4xx other than 429 are not
+// retried.
+func doWithRetry(token string, body []byte) ([]byte, int, error) {
+	var lastErr error
+	for attempt := 0; attempt < maxRetries; attempt++ {
+		if attempt > 0 {
+			log.Printf("retry attempt %d after %v: %v", attempt, retryBackoff[attempt-1], lastErr)
+			time.Sleep(retryBackoff[attempt-1])
+		}
+
+		req, err := http.NewRequest("POST", "https://api.github.com/graphql", bytes.NewReader(body))
+		if err != nil {
+			return nil, 0, err
+		}
+		req.Header.Set("Authorization", "Bearer "+token)
+		req.Header.Set("Content-Type", "application/json")
+		req.Header.Set("User-Agent", "awesome-coding-agents-updater")
+
+		resp, err := httpClient.Do(req)
+		if err != nil {
+			lastErr = err
+			continue // network error — retry
+		}
+
+		raw, err := io.ReadAll(resp.Body)
+		resp.Body.Close()
+		if err != nil {
+			lastErr = fmt.Errorf("read body: %w", err)
+			continue
+		}
+
+		sc := resp.StatusCode
+		if sc == http.StatusOK {
+			return raw, sc, nil
+		}
+		if sc == http.StatusTooManyRequests || sc >= 500 {
+			lastErr = fmt.Errorf("HTTP %d: %s", sc, raw)
+			continue // retryable
+		}
+		// 4xx (except 429) — not retryable
+		return raw, sc, nil
+	}
+	return nil, 0, fmt.Errorf("all %d attempts failed; last error: %w", maxRetries, lastErr)
 }
diff --git a/history.go b/history.go
index a813b5a..034374b 100644
--- a/history.go
+++ b/history.go
@@ -3,7 +3,9 @@ package main
 import (
 	"bufio"
 	"encoding/json"
+	"fmt"
 	"os"
+	"slices"
 	"time"
 )
 
@@ -12,11 +14,24 @@ type Snapshot struct {
 	Stars map[string]int `json:"stars"`
 }
 
+// canonicalKeyMigrations remaps old history keys to the current canonical
+// owner/repo from agents.yml. Add entries here when a tracked repo is renamed
+// and history.jsonl contains the old name.
+//
+// Known renames:
+//   - block/goose was formerly tracked as aaif-goose/goose
+var canonicalKeyMigrations = map[string]string{
+	"aaif-goose/goose": "block/goose",
+}
+
 func appendHistory(path string, stats []Stat) (map[string]int, error) {
 	today := time.Now().UTC().Format("2006-01-02")
+
+	// Key snapshots by canonical owner/repo from agents.yml, not by the
+	// API-returned nameWithOwner, so renames don't orphan historical data.
 	current := Snapshot{Date: today, Stars: map[string]int{}}
 	for _, s := range stats {
-		current.Stars[s.NameWithOwner] = s.Stars
+		current.Stars[s.CanonicalKey] = s.Stars
 	}
 
 	snapshots, err := readSnapshots(path)
@@ -26,13 +41,8 @@ func appendHistory(path string, stats []Stat) (map[string]int, error) {
 
 	deltas := computeDeltas(snapshots, current)
 
-	// drop any pre-existing snapshot for today, then append current
-	kept := snapshots[:0]
-	for _, s := range snapshots {
-		if s.Date != today {
-			kept = append(kept, s)
-		}
-	}
+	// Drop any pre-existing snapshot for today, then append current.
+	kept := slices.DeleteFunc(snapshots, func(s Snapshot) bool { return s.Date == today })
 	kept = append(kept, current)
 
 	return deltas, writeSnapshots(path, kept)
@@ -51,45 +61,89 @@ func readSnapshots(path string) ([]Snapshot, error) {
 	var out []Snapshot
 	scanner := bufio.NewScanner(f)
 	scanner.Buffer(make([]byte, 1024*1024), 16*1024*1024)
+	lineNum := 0
 	for scanner.Scan() {
+		lineNum++
 		line := scanner.Bytes()
 		if len(line) == 0 {
 			continue
 		}
 		var s Snapshot
 		if err := json.Unmarshal(line, &s); err != nil {
-			// skip malformed lines rather than fail the whole run
+			// Log corruption so it's observable; don't silently drop lines.
+			fmt.Fprintf(os.Stderr, "history.jsonl line %d: skipping malformed entry: %v\n", lineNum, err)
 			continue
 		}
+		// Apply canonical-key migrations so history keyed under old names is
+		// transparently remapped to the current agents.yml canonical key.
+		s.Stars = applyMigrations(s.Stars)
 		out = append(out, s)
 	}
 	return out, scanner.Err()
 }
 
+// applyMigrations rewrites any deprecated history keys to their current
+// canonical form. Old keys are removed; new keys accumulate stars additively
+// (in practice the old key had no concurrent new entry, so max is the same).
+func applyMigrations(stars map[string]int) map[string]int {
+	for old, canonical := range canonicalKeyMigrations {
+		if v, ok := stars[old]; ok {
+			if stars[canonical] < v {
+				stars[canonical] = v
+			}
+			delete(stars, old)
+		}
+	}
+	return stars
+}
+
+// writeSnapshots writes to a temp file then renames atomically so a crash
+// mid-write never leaves history.jsonl truncated or partially written.
 func writeSnapshots(path string, snapshots []Snapshot) error {
-	f, err := os.Create(path)
+	tmp := path + ".tmp"
+	f, err := os.Create(tmp)
 	if err != nil {
 		return err
 	}
-	defer f.Close()
+
 	enc := json.NewEncoder(f)
+	writeErr := error(nil)
 	for _, s := range snapshots {
 		if err := enc.Encode(s); err != nil {
-			return err
+			writeErr = err
+			break
 		}
 	}
-	return nil
+
+	if syncErr := f.Sync(); syncErr != nil && writeErr == nil {
+		writeErr = syncErr
+	}
+	f.Close()
+
+	if writeErr != nil {
+		os.Remove(tmp)
+		return writeErr
+	}
+
+	return os.Rename(tmp, path)
 }
 
-// computeDeltas returns stars-now minus stars-at-or-before-cutoff for each repo.
-// Cutoff = 7 days ago UTC. If no snapshot is old enough, delta is omitted.
+// computeDeltas returns stars-now minus stars-at-or-before-cutoff for each
+// repo. Cutoff = 7 days ago UTC. The chosen prior snapshot must be within a
+// 3-day window of the cutoff; if cron was skipped for more than 10 days the
+// delta would be misleadingly labeled "Δ7d", so we return no delta instead.
 func computeDeltas(history []Snapshot, current Snapshot) map[string]int {
 	deltas := map[string]int{}
-	cutoff := time.Now().UTC().AddDate(0, 0, -7).Format("2006-01-02")
+	now := time.Now().UTC()
+	cutoff := now.AddDate(0, 0, -7).Format("2006-01-02")
+	// Accept snapshots in (cutoff - 3 days, cutoff]. A snapshot older than
+	// cutoff-3d is too stale to label as a 7-day delta.
+	lowerBound := now.AddDate(0, 0, -10).Format("2006-01-02")
 
 	var base *Snapshot
 	for i := range history {
-		if history[i].Date <= cutoff {
+		d := history[i].Date
+		if d > lowerBound && d <= cutoff {
 			base = &history[i]
 		}
 	}
diff --git a/history_test.go b/history_test.go
new file mode 100644
index 0000000..2b6630e
--- /dev/null
+++ b/history_test.go
@@ -0,0 +1,228 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"os"
+	"testing"
+	"time"
+)
+
+func TestComputeDeltas_NoHistory(t *testing.T) {
+	// Empty history slice should return empty delta map without panicking.
+	current := Snapshot{
+		Date: "2026-05-14",
+		Stars: map[string]int{
+			"org/repo": 100,
+		},
+	}
+	deltas := computeDeltas(nil, current)
+	if deltas == nil {
+		t.Errorf("expected non-nil empty map, got nil")
+	}
+	if len(deltas) != 0 {
+		t.Errorf("expected empty deltas, got %d entries", len(deltas))
+	}
+}
+
+func TestComputeDeltas_SevenDayWindow(t *testing.T) {
+	// The cutoff window is (cutoff-3d, cutoff] where cutoff = now - 7d.
+	// So valid snapshots have date in range (now-10d, now-7d].
+
+	now := time.Now().UTC()
+	today := now.Format("2006-01-02")
+
+	tests := []struct {
+		name      string
+		daysAgo   int
+		expectDelta bool
+		desc      string
+	}{
+		{
+			name:        "snapshot at exactly 7 days ago",
+			daysAgo:     7,
+			expectDelta: true,
+			desc:        "at cutoff boundary — should be included",
+		},
+		{
+			name:        "snapshot at 9 days ago",
+			daysAgo:     9,
+			expectDelta: true,
+			desc:        "within (cutoff-3d, cutoff] — should be included",
+		},
+		{
+			name:        "snapshot at 11 days ago",
+			daysAgo:     11,
+			expectDelta: false,
+			desc:        "older than cutoff-3d — should be excluded",
+		},
+		{
+			name:        "snapshot at 6 days ago",
+			daysAgo:     6,
+			expectDelta: false,
+			desc:        "newer than cutoff — should be excluded",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			snapshotDate := now.AddDate(0, 0, -tt.daysAgo).Format("2006-01-02")
+			history := []Snapshot{
+				{
+					Date: snapshotDate,
+					Stars: map[string]int{
+						"org/repo": 100,
+					},
+				},
+			}
+			current := Snapshot{
+				Date: today,
+				Stars: map[string]int{
+					"org/repo": 150,
+				},
+			}
+			deltas := computeDeltas(history, current)
+
+			if tt.expectDelta {
+				if len(deltas) == 0 {
+					t.Errorf("%s: expected delta for 'org/repo', got empty map", tt.desc)
+				}
+				if delta, ok := deltas["org/repo"]; !ok || delta != 50 {
+					t.Errorf("%s: expected delta=50, got %v", tt.desc, delta)
+				}
+			} else {
+				if len(deltas) > 0 {
+					t.Errorf("%s: expected no delta, got %v", tt.desc, deltas)
+				}
+			}
+		})
+	}
+}
+
+func TestReadSnapshots_MalformedLine(t *testing.T) {
+	// Temp JSONL with: valid, malformed, empty, valid lines.
+	// Should skip malformed/empty and return only the 2 valid snapshots.
+
+	tmpDir := t.TempDir()
+	tmpFile := tmpDir + "/history.jsonl"
+
+	content := `{"date":"2026-05-01","stars":{"org/repo":100}}
+not json at all { bad
+{"date":"2026-05-02","stars":{"org/repo":200}}
+{"date":"2026-05-03","stars":{"org/repo":300}}
+`
+
+	if err := os.WriteFile(tmpFile, []byte(content), 0600); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	snapshots, err := readSnapshots(tmpFile)
+	if err != nil {
+		t.Fatalf("readSnapshots failed: %v", err)
+	}
+
+	if len(snapshots) != 3 {
+		t.Errorf("expected 3 snapshots (skipped 1 malformed), got %d", len(snapshots))
+	}
+
+	// Check dates are in order.
+	if len(snapshots) >= 3 {
+		if snapshots[0].Date != "2026-05-01" {
+			t.Errorf("snapshot[0] date: expected 2026-05-01, got %s", snapshots[0].Date)
+		}
+		if snapshots[1].Date != "2026-05-02" {
+			t.Errorf("snapshot[1] date: expected 2026-05-02, got %s", snapshots[1].Date)
+		}
+		if snapshots[2].Date != "2026-05-03" {
+			t.Errorf("snapshot[2] date: expected 2026-05-03, got %s", snapshots[2].Date)
+		}
+	}
+}
+
+func TestReadSnapshots_MissingFile(t *testing.T) {
+	// Non-existent file should return nil with no error (not os.IsNotExist error).
+	snapshots, err := readSnapshots("/nonexistent/path/history.jsonl")
+	if err != nil {
+		t.Errorf("expected nil error on missing file, got %v", err)
+	}
+	if snapshots != nil {
+		t.Errorf("expected nil snapshots on missing file, got %v", snapshots)
+	}
+}
+
+func TestApplyMigrations(t *testing.T) {
+	// Test the canonical key migration logic.
+	stars := map[string]int{
+		"aaif-goose/goose": 45115,
+		"other/repo":       1000,
+	}
+
+	result := applyMigrations(stars)
+
+	// The old key should be removed.
+	if _, ok := result["aaif-goose/goose"]; ok {
+		t.Errorf("old key 'aaif-goose/goose' should be removed")
+	}
+
+	// The new key should be present with the value.
+	if v, ok := result["block/goose"]; !ok || v != 45115 {
+		t.Errorf("new key 'block/goose': expected 45115, got %v", v)
+	}
+
+	// Other keys should be unchanged.
+	if v, ok := result["other/repo"]; !ok || v != 1000 {
+		t.Errorf("'other/repo': expected 1000, got %v", v)
+	}
+}
+
+func TestWriteSnapshots_AtomicWrite(t *testing.T) {
+	// Verify that writeSnapshots uses atomic rename (writes to .tmp first).
+	tmpDir := t.TempDir()
+	tmpFile := tmpDir + "/history.jsonl"
+
+	snapshots := []Snapshot{
+		{Date: "2026-05-01", Stars: map[string]int{"org/repo": 100}},
+		{Date: "2026-05-02", Stars: map[string]int{"org/repo": 200}},
+	}
+
+	err := writeSnapshots(tmpFile, snapshots)
+	if err != nil {
+		t.Fatalf("writeSnapshots failed: %v", err)
+	}
+
+	// Verify file exists and has correct content.
+	if _, err := os.Stat(tmpFile); err != nil {
+		t.Fatalf("output file missing: %v", err)
+	}
+
+	content, err := os.ReadFile(tmpFile)
+	if err != nil {
+		t.Fatalf("ReadFile failed: %v", err)
+	}
+
+	// Verify JSON is valid and correct.
+	var readBack []Snapshot
+	decoder := json.NewDecoder(bytes.NewReader(content))
+	for decoder.More() {
+		var s Snapshot
+		if err := decoder.Decode(&s); err != nil {
+			t.Fatalf("decode failed: %v", err)
+		}
+		readBack = append(readBack, s)
+	}
+
+	if len(readBack) != 2 {
+		t.Errorf("expected 2 snapshots, got %d", len(readBack))
+	}
+	if readBack[0].Date != "2026-05-01" || readBack[0].Stars["org/repo"] != 100 {
+		t.Errorf("snapshot 0 mismatch: %+v", readBack[0])
+	}
+	if readBack[1].Date != "2026-05-02" || readBack[1].Stars["org/repo"] != 200 {
+		t.Errorf("snapshot 1 mismatch: %+v", readBack[1])
+	}
+
+	// .tmp file should not exist (cleaned up after rename).
+	if _, err := os.Stat(tmpFile + ".tmp"); !os.IsNotExist(err) {
+		t.Errorf("temp file should not exist after successful write")
+	}
+}
diff --git a/main.go b/main.go
index ee88d1e..8c80f9f 100644
--- a/main.go
+++ b/main.go
@@ -15,7 +15,7 @@ func main() {
 func run() error {
 	agents, err := loadAgents("data/agents.yml")
 	if err != nil {
-		return fmt.Errorf("load agents: %w", err)
+		return err
 	}
 	if len(agents) == 0 {
 		return fmt.Errorf("no agents in data/agents.yml")
@@ -28,18 +28,16 @@ func run() error {
 
 	stats, err := fetchStats(token, agents)
 	if err != nil {
-		return fmt.Errorf("fetch stats: %w", err)
+		return err
 	}
 
-	sortByStars(stats)
-
 	deltas, err := appendHistory("data/history.jsonl", stats)
 	if err != nil {
-		return fmt.Errorf("append history: %w", err)
+		return err
 	}
 
 	if err := renderReadme("templates/readme.tmpl", "README.md", stats, deltas); err != nil {
-		return fmt.Errorf("render readme: %w", err)
+		return err
 	}
 
 	fmt.Printf("updated %d agents\n", len(stats))
diff --git a/readme.go b/readme.go
index 71502bf..a09cf1f 100644
--- a/readme.go
+++ b/readme.go
@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 	"strings"
 	"text/template"
 	"time"
@@ -24,7 +25,8 @@ type Row struct {
 func renderReadme(tmplPath, outPath string, stats []Stat, deltas map[string]int) error {
 	rows := make([]Row, len(stats))
 	for i, s := range stats {
-		delta, has := deltas[s.NameWithOwner]
+		// Deltas are keyed by CanonicalKey (owner/repo from agents.yml).
+		delta, has := deltas[s.CanonicalKey]
 		rows[i] = Row{
 			Rank:          i + 1,
 			NameWithOwner: s.NameWithOwner,
@@ -75,12 +77,7 @@ func renderReadme(tmplPath, outPath string, stats []Stat, deltas map[string]int)
 	}
 	defer f.Close()
 
-	name := tmplPath
-	if i := strings.LastIndex(tmplPath, "/"); i >= 0 {
-		name = tmplPath[i+1:]
-	}
-
-	return tmpl.ExecuteTemplate(f, name, map[string]any{
+	return tmpl.ExecuteTemplate(f, filepath.Base(tmplPath), map[string]any{
 		"Rows":      rows,
 		"UpdatedAt": time.Now().UTC().Format("2006-01-02 15:04 UTC"),
 		"Total":     len(rows),
diff --git a/readme_test.go b/readme_test.go
new file mode 100644
index 0000000..0291c6e
--- /dev/null
+++ b/readme_test.go
@@ -0,0 +1,96 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestSanitizeCell(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected string
+		desc     string
+	}{
+		{
+			name:     "plain text",
+			input:    "hello world",
+			expected: "hello world",
+			desc:     "unchanged",
+		},
+		{
+			name:     "pipe char",
+			input:    "foo | bar",
+			expected: "foo \\| bar",
+			desc:     "pipe escaped",
+		},
+		{
+			name:     "newline",
+			input:    "line1\nline2",
+			expected: "line1 line2",
+			desc:     "newline becomes space",
+		},
+		{
+			name:     "carriage return",
+			input:    "line1\rline2",
+			expected: "line1 line2",
+			desc:     "carriage return becomes space",
+		},
+		{
+			name:     "pipe and newline",
+			input:    "foo | bar\nbaz",
+			expected: "foo \\| bar baz",
+			desc:     "both handled correctly",
+		},
+		{
+			name:     "empty string",
+			input:    "",
+			expected: "",
+			desc:     "empty string unchanged",
+		},
+		{
+			name:     "multiple pipes",
+			input:    "a | b | c",
+			expected: "a \\| b \\| c",
+			desc:     "multiple pipes escaped",
+		},
+		{
+			name:     "multiple newlines",
+			input:    "line1\n\nline2",
+			expected: "line1  line2",
+			desc:     "multiple newlines become spaces",
+		},
+		{
+			name:     "whitespace trimming",
+			input:    "  text  ",
+			expected: "text",
+			desc:     "leading/trailing spaces trimmed",
+		},
+		{
+			name:     "complex: whitespace, pipe, newline",
+			input:    "  foo | bar\nbaz  ",
+			expected: "foo \\| bar baz",
+			desc:     "all transformations applied",
+		},
+		{
+			name:     "only newlines and pipes",
+			input:    "|\n|",
+			expected: "\\| \\|",
+			desc:     "pipes and newlines only",
+		},
+		{
+			name:     "mixed line endings",
+			input:    "line1\nline2\rline3",
+			expected: "line1 line2 line3",
+			desc:     "both \\n and \\r converted",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := sanitizeCell(tt.input)
+			if result != tt.expected {
+				t.Errorf("%s: expected %q, got %q", tt.desc, tt.expected, result)
+			}
+		})
+	}
+}