feat(config): add TAPIR_ONBOARD_SUMMARIZE_COUNT (default 3, hard cap 5)

Bounds the connect-time onboarding summary burst (Feature 1). Hard-capped at 5
and clamped (negative->0, >cap->cap) so onboarding can never bulk-fetch; 0
disables. The cap bounds COUNT only — every fetch still flows through the shared
caption rate gate (ADR-014).

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

internal/config/config.go

@@ -13,6 +13,7 @@ import (
 	"os"
 	"path/filepath"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -79,6 +80,13 @@ type Config struct {
 	// pre-recency behaviour). Default ~7 days.
 	AutoSummarizeWindow time.Duration
 
+	// OnboardSummarizeCount caps how many of a freshly-connected user's newest
+	// videos are summarized immediately on connect (the onboarding "it works"
+	// burst). HARD-capped at maxOnboardSummarizeCount so onboarding can never
+	// bulk-fetch; 0 disables the burst. Every fetch still flows through the shared
+	// caption rate gate (ADR-014) — the cap bounds count, never the pacing. Default 3.
+	OnboardSummarizeCount int
+
 	// DiscoveryInterval, when > 0, makes `serve` run in-process scheduled discovery
 	// for ALL users on that cadence (ADR-018). Zero/unset = disabled, so dev and
 	// tests never auto-fetch. Single-replica assumption — see cmdServe.
@@ -108,17 +116,19 @@ func (c Config) DexConfigured() bool { return strings.TrimSpace(c.OIDCIssuer) !=
 
 // Defaults (see docs/homelab-integration.md). All overridable via env.
 const (
-	defaultGatewayURL           = "http://koala:30401/v1"
-	defaultSummarizerModel      = "koala/phi4-mini"
-	defaultSummarizerTimeout    = 5 * time.Minute
-	defaultYTTokenRef           = "youtube/refresh_token"
-	defaultYTConnectRedirectURL = "https://tapir.d-ma.be/oauth/youtube/callback"
-	defaultOAuthRedirectAddr    = "localhost:8080"
-	defaultHTTPAddr             = ":8080"
-	defaultFetchBackoff         = time.Hour
-	defaultFetchRate            = 2 * time.Second
-	defaultPublicURL            = "https://tapir.d-ma.be"
-	defaultAutoSummarizeWindow  = 7 * 24 * time.Hour
+	defaultGatewayURL            = "http://koala:30401/v1"
+	defaultSummarizerModel       = "koala/phi4-mini"
+	defaultSummarizerTimeout     = 5 * time.Minute
+	defaultYTTokenRef            = "youtube/refresh_token"
+	defaultYTConnectRedirectURL  = "https://tapir.d-ma.be/oauth/youtube/callback"
+	defaultOAuthRedirectAddr     = "localhost:8080"
+	defaultHTTPAddr              = ":8080"
+	defaultFetchBackoff          = time.Hour
+	defaultFetchRate             = 2 * time.Second
+	defaultPublicURL             = "https://tapir.d-ma.be"
+	defaultAutoSummarizeWindow   = 7 * 24 * time.Hour
+	defaultOnboardSummarizeCount = 3
+	maxOnboardSummarizeCount     = 5
 )
 
 // Load reads the environment into a Config, applying defaults. It does not
@@ -183,6 +193,18 @@ func Load() (Config, error) {
 	}
 	c.AutoSummarizeWindow = autoWindow
 
+	onboard, err := intOr("TAPIR_ONBOARD_SUMMARIZE_COUNT", defaultOnboardSummarizeCount)
+	if err != nil {
+		return Config{}, err
+	}
+	if onboard < 0 {
+		onboard = 0
+	}
+	if onboard > maxOnboardSummarizeCount {
+		onboard = maxOnboardSummarizeCount
+	}
+	c.OnboardSummarizeCount = onboard
+
 	return c, nil
 }
 
@@ -247,6 +269,18 @@ func envOr(key, fallback string) string {
 	return fallback
 }
 
+func intOr(key string, fallback int) (int, error) {
+	v := os.Getenv(key)
+	if v == "" {
+		return fallback, nil
+	}
+	n, err := strconv.Atoi(v)
+	if err != nil {
+		return 0, fmt.Errorf("config: %s=%q: %w", key, v, err)
+	}
+	return n, nil
+}
+
 func durationOr(key string, fallback time.Duration) (time.Duration, error) {
 	v := os.Getenv(key)
 	if v == "" {

internal/config/config_test.go

@@ -53,6 +53,38 @@ func TestLoad_AppliesDefaults(t *testing.T) {
 	}
 }
 
+func TestLoad_OnboardSummarizeCount(t *testing.T) {
+	cases := []struct {
+		name, env string
+		want      int
+	}{
+		{"default", "", defaultOnboardSummarizeCount},
+		{"explicit", "4", 4},
+		{"zero disables", "0", 0},
+		{"clamped to hard cap", "50", maxOnboardSummarizeCount},
+		{"negative clamps to zero", "-3", 0},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			setEnv(t, map[string]string{"TAPIR_ONBOARD_SUMMARIZE_COUNT": c.env})
+			cfg, err := Load()
+			if err != nil {
+				t.Fatalf("Load: %v", err)
+			}
+			if cfg.OnboardSummarizeCount != c.want {
+				t.Fatalf("OnboardSummarizeCount = %d, want %d", cfg.OnboardSummarizeCount, c.want)
+			}
+		})
+	}
+}
+
+func TestLoad_OnboardSummarizeCountInvalid(t *testing.T) {
+	setEnv(t, map[string]string{"TAPIR_ONBOARD_SUMMARIZE_COUNT": "three"})
+	if _, err := Load(); err == nil {
+		t.Fatal("Load: want error for non-numeric TAPIR_ONBOARD_SUMMARIZE_COUNT")
+	}
+}
+
 func TestLoad_ParsesValues(t *testing.T) {
 	setEnv(t, map[string]string{
 		"TAPIR_USER_ID":               "11111111-1111-1111-1111-111111111111",