feat(podcasts): constrain monologue briefs to a single speaker

surfsense_backend/app/podcasts/schemas/spec.py

@@ -148,6 +148,14 @@ class PodcastSpec(BaseModel):
             raise ValueError("speaker slots must be unique")
         return self
 
+    @model_validator(mode="after")
+    def _check_style_speakers(self) -> PodcastSpec:
+        # One voice is what "monologue" means; letting extra speakers through
+        # would force drafting to silently pick a winner.
+        if self.style is PodcastStyle.MONOLOGUE and len(self.speakers) != 1:
+            raise ValueError("a monologue has exactly one speaker")
+        return self
+
     def speaker_for(self, slot: int) -> SpeakerSpec:
         """Return the speaker bound to ``slot`` or raise if none matches."""
         for speaker in self.speakers:

surfsense_backend/tests/unit/podcasts/test_spec.py

@@ -14,6 +14,7 @@ from pydantic import ValidationError
 from app.podcasts.schemas import (
     DurationTarget,
     PodcastSpec,
+    PodcastStyle,
     SpeakerRole,
     SpeakerSpec,
     Transcript,
@@ -80,6 +81,27 @@ def test_a_brief_needs_at_least_one_speaker():
         )
 
 
+def test_a_monologue_brief_carries_exactly_one_speaker():
+    spec = PodcastSpec(
+        language="en",
+        style=PodcastStyle.MONOLOGUE,
+        speakers=[_speaker(0)],
+        duration=DurationTarget(min_minutes=5, max_minutes=10),
+    )
+    assert spec.style is PodcastStyle.MONOLOGUE
+
+
+def test_a_monologue_brief_rejects_multiple_speakers():
+    """One voice is what 'monologue' means; a second speaker is a user error."""
+    with pytest.raises(ValidationError):
+        PodcastSpec(
+            language="en",
+            style=PodcastStyle.MONOLOGUE,
+            speakers=[_speaker(0), _speaker(1, voice_id="kokoro:af_bella")],
+            duration=DurationTarget(min_minutes=5, max_minutes=10),
+        )
+
+
 def test_duration_rejects_an_inverted_range():
     """A max below the min is a user error caught at the brief gate."""
     with pytest.raises(ValidationError):

surfsense_web/components/tool-ui/podcast/brief-review.tsx

@@ -110,6 +110,16 @@ export function BriefReview({ podcast, spec }: BriefReviewProps) {
 		});
 	};
 
+	const setStyle = (style: PodcastStyle) => {
+		setDraft((current) => ({
+			...current,
+			style,
+			// A monologue has exactly one speaker, so extra speakers are dropped
+			// rather than letting approval fail validation.
+			speakers: style === "monologue" ? current.speakers.slice(0, 1) : current.speakers,
+		}));
+	};
+
 	const updateSpeaker = (slot: number, change: Partial<PodcastSpec["speakers"][number]>) => {
 		setDraft((current) => ({
 			...current,
@@ -198,12 +208,7 @@ export function BriefReview({ podcast, spec }: BriefReviewProps) {
 				</div>
 				<div className="flex flex-col gap-2">
 					<Label htmlFor="podcast-style">Style</Label>
-					<Select
-						value={draft.style}
-						onValueChange={(value) =>
-							setDraft((current) => ({ ...current, style: value as PodcastStyle }))
-						}
-					>
+					<Select value={draft.style} onValueChange={(value) => setStyle(value as PodcastStyle)}>
 						<SelectTrigger id="podcast-style">
 							<SelectValue placeholder="Style" />
 						</SelectTrigger>
@@ -226,7 +231,7 @@ export function BriefReview({ podcast, spec }: BriefReviewProps) {
 						variant="ghost"
 						size="sm"
 						onClick={addSpeaker}
-						disabled={draft.speakers.length >= MAX_SPEAKERS}
+						disabled={draft.style === "monologue" || draft.speakers.length >= MAX_SPEAKERS}
 					>
 						<Plus className="size-4" /> Add speaker
 					</Button>

surfsense_web/contracts/types/podcast.types.ts

@@ -61,13 +61,19 @@ export const durationTarget = z.object({
 });
 export type DurationTarget = z.infer<typeof durationTarget>;
 
-export const podcastSpec = z.object({
-	language: z.string().min(2),
-	style: podcastStyle,
-	speakers: z.array(speakerSpec).min(1).max(MAX_SPEAKERS),
-	duration: durationTarget,
-	focus: z.string().max(2000).nullable().optional(),
-});
+export const podcastSpec = z
+	.object({
+		language: z.string().min(2),
+		style: podcastStyle,
+		speakers: z.array(speakerSpec).min(1).max(MAX_SPEAKERS),
+		duration: durationTarget,
+		focus: z.string().max(2000).nullable().optional(),
+	})
+	// Mirrors the backend invariant: one voice is what "monologue" means.
+	.refine((spec) => spec.style !== "monologue" || spec.speakers.length === 1, {
+		message: "A monologue has exactly one speaker",
+		path: ["speakers"],
+	});
 export type PodcastSpec = z.infer<typeof podcastSpec>;
 
 // =============================================================================