feat(config): TAPIR_FETCH_BACKOFF for rate-limit retry window

Adds FetchBackoff (Go duration, default 1h) controlling how long the run loop
waits before re-fetching a transcript that returned HTTP 429. Zero means always
retry. Not required by ValidateForRun — a zero/unset value is a valid policy.

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

internal/config/config.go

@@ -59,6 +59,12 @@ type Config struct {
 	// PollInterval, when > 0, makes `run` loop on that cadence; 0 means run once.
 	PollInterval time.Duration
 
+	// FetchBackoff is how long the run loop waits before re-fetching a transcript
+	// that previously returned HTTP 429 (rate_limited). Inside the window the video
+	// is skipped without hitting the caption endpoint, saving requests; after it
+	// expires the video is retried. Zero means "always retry" (no backoff).
+	FetchBackoff time.Duration
+
 	// HTTPAddr is the listen address for `tapir serve` (the Stage-0 web UI).
 	HTTPAddr string
 
@@ -85,6 +91,7 @@ const (
 	defaultYTConnectRedirectURL = "https://tapir.d-ma.be/oauth/youtube/callback"
 	defaultOAuthRedirectAddr    = "localhost:8080"
 	defaultHTTPAddr             = ":8080"
+	defaultFetchBackoff         = time.Hour
 )
 
 // Load reads the environment into a Config, applying defaults. It does not
@@ -124,6 +131,12 @@ func Load() (Config, error) {
 	}
 	c.PollInterval = interval
 
+	backoff, err := durationOr("TAPIR_FETCH_BACKOFF", defaultFetchBackoff)
+	if err != nil {
+		return Config{}, err
+	}
+	c.FetchBackoff = backoff
+
 	return c, nil
 }
 

internal/config/config_test.go

@@ -45,6 +45,9 @@ func TestLoad_AppliesDefaults(t *testing.T) {
 	if c.PollInterval != 0 {
 		t.Errorf("PollInterval = %v, want 0 (run once)", c.PollInterval)
 	}
+	if c.FetchBackoff != defaultFetchBackoff {
+		t.Errorf("FetchBackoff = %v, want default %v", c.FetchBackoff, defaultFetchBackoff)
+	}
 }
 
 func TestLoad_ParsesValues(t *testing.T) {
@@ -56,6 +59,7 @@ func TestLoad_ParsesValues(t *testing.T) {
 		"TAPIR_SUMMARIZER_TIMEOUT": "90s",
 		"TAPIR_DB_DSN":             "postgres://x",
 		"TAPIR_POLL_INTERVAL":      "10m",
+		"TAPIR_FETCH_BACKOFF":      "30m",
 	})
 
 	c, err := Load()
@@ -77,6 +81,9 @@ func TestLoad_ParsesValues(t *testing.T) {
 	if c.PollInterval != 10*time.Minute {
 		t.Errorf("PollInterval = %v, want 10m", c.PollInterval)
 	}
+	if c.FetchBackoff != 30*time.Minute {
+		t.Errorf("FetchBackoff = %v, want 30m", c.FetchBackoff)
+	}
 }
 
 func TestLoad_RejectsBadDuration(t *testing.T) {