feat(config): add OnboardSummarizerModel + OnboardMaxVideoSeconds (ADR-028)

Two knobs for the onboarding-burst quality work:
- TAPIR_ONBOARD_SUMMARIZER_MODEL (default iguana/gemma4-26b): the stronger model
  the burst leads its chain with; empty collapses the burst onto the shared
  processor (lookupOr, so explicit-empty disables).
- TAPIR_ONBOARD_MAX_VIDEO_SECONDS (default 14400/4h): upper duration bound for
  burst picks; 0 disables, negative clamps to 0.

Table-driven tests cover defaults, explicit, disable, and invalid input.

internal/config/config.go

@@ -120,6 +120,21 @@ type Config struct {
 	// caption rate gate (ADR-014) — the cap bounds count, never the pacing. Default 3.
 	OnboardSummarizeCount int
 
+	// OnboardSummarizerModel is the summarizer alias the connect-time burst leads
+	// its chain with (ADR-028) — a stronger model is affordable on the ≤3 summaries
+	// that form a new user's first impression. It heads a burst-specific chain;
+	// the standard chain (ADR-022) follows as resilience. Empty (or equal to
+	// SummarizerModel) collapses the burst back onto the shared processor — the
+	// reversibility lever. Default iguana/gemma4-26b (the brain-validated model).
+	OnboardSummarizerModel string
+
+	// OnboardMaxVideoSeconds upper-bounds the duration of a video the onboarding
+	// burst will pick (ADR-028), so the burst does not spend a scarce caption fetch
+	// on a multi-hour livestream VOD that passed the live filter once it ended. Only
+	// a KNOWN duration outside [MinVideoSeconds, this] is dropped; a NULL/unknown
+	// duration is kept (degrade-open). 0 disables the upper bound. Default 14400 (4h).
+	OnboardMaxVideoSeconds 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.
@@ -169,6 +184,8 @@ const (
 	defaultAutoSummarizeWindow    = 7 * 24 * time.Hour
 	defaultOnboardSummarizeCount  = 3
 	maxOnboardSummarizeCount      = 5
+	defaultOnboardSummarizerModel = "iguana/gemma4-26b"
+	defaultOnboardMaxVideoSeconds = 14400 // 4h
 )
 
 // Load reads the environment into a Config, applying defaults. It does not
@@ -181,6 +198,7 @@ func Load() (Config, error) {
 		GatewayURL:             envOr("TAPIR_GATEWAY_URL", defaultGatewayURL),
 		GatewayKey:             os.Getenv("TAPIR_GATEWAY_KEY"),
 		SummarizerModel:        envOr("TAPIR_SUMMARIZER_MODEL", defaultSummarizerModel),
+		OnboardSummarizerModel: lookupOr("TAPIR_ONBOARD_SUMMARIZER_MODEL", defaultOnboardSummarizerModel),
 		FallbackModel:          lookupOr("TAPIR_FALLBACK_MODEL", defaultFallbackModel),
 		CloudFallbackModel:     lookupOr("TAPIR_CLOUD_FALLBACK_MODEL", defaultCloudFallbackModel),
 		DBDSN:                  os.Getenv("TAPIR_DB_DSN"),
@@ -286,6 +304,15 @@ func Load() (Config, error) {
 	}
 	c.OnboardSummarizeCount = onboard
 
+	onboardMax, err := intOr("TAPIR_ONBOARD_MAX_VIDEO_SECONDS", defaultOnboardMaxVideoSeconds)
+	if err != nil {
+		return Config{}, err
+	}
+	if onboardMax < 0 {
+		onboardMax = 0
+	}
+	c.OnboardMaxVideoSeconds = onboardMax
+
 	return c, nil
 }
 

internal/config/config_test.go

@@ -214,3 +214,62 @@ func TestValidateForAuth_PassesWhenComplete(t *testing.T) {
 		t.Errorf("ValidateForAuth: unexpected error %v", err)
 	}
 }
+
+func TestLoad_OnboardSummarizerModel(t *testing.T) {
+	cases := []struct {
+		name, env string
+		set       bool
+		want      string
+	}{
+		{"default", "", false, defaultOnboardSummarizerModel},
+		{"explicit", "koala/some-model", true, "koala/some-model"},
+		{"empty disables (collapses to shared processor)", "", true, ""},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			env := map[string]string{}
+			if c.set {
+				env["TAPIR_ONBOARD_SUMMARIZER_MODEL"] = c.env
+			}
+			setEnv(t, env)
+			cfg, err := Load()
+			if err != nil {
+				t.Fatalf("Load: %v", err)
+			}
+			if cfg.OnboardSummarizerModel != c.want {
+				t.Fatalf("OnboardSummarizerModel = %q, want %q", cfg.OnboardSummarizerModel, c.want)
+			}
+		})
+	}
+}
+
+func TestLoad_OnboardMaxVideoSeconds(t *testing.T) {
+	cases := []struct {
+		name, env string
+		want      int
+	}{
+		{"default", "", defaultOnboardMaxVideoSeconds},
+		{"explicit", "7200", 7200},
+		{"zero disables", "0", 0},
+		{"negative clamps to zero", "-9", 0},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			setEnv(t, map[string]string{"TAPIR_ONBOARD_MAX_VIDEO_SECONDS": c.env})
+			cfg, err := Load()
+			if err != nil {
+				t.Fatalf("Load: %v", err)
+			}
+			if cfg.OnboardMaxVideoSeconds != c.want {
+				t.Fatalf("OnboardMaxVideoSeconds = %d, want %d", cfg.OnboardMaxVideoSeconds, c.want)
+			}
+		})
+	}
+}
+
+func TestLoad_OnboardMaxVideoSecondsInvalid(t *testing.T) {
+	setEnv(t, map[string]string{"TAPIR_ONBOARD_MAX_VIDEO_SECONDS": "long"})
+	if _, err := Load(); err == nil {
+		t.Fatal("Load: want error for non-numeric TAPIR_ONBOARD_MAX_VIDEO_SECONDS")
+	}
+}