Detect topic boundaries as continuous segments

src/meeting_lab/segmentation/segment_topics.py

@@ -1,20 +1,23 @@
 #!/usr/bin/env python3
 """
-Segment a normalized meeting transcript into discussion topics using Ollama.
+Detect topic boundaries in a normalized meeting transcript using Ollama.
 
-The script numbers the transcript blocks and asks the language model only to
-identify the thematic structure of the discussion.
+The language model only identifies positions at which the discussion topic
+changes. Python then converts those boundaries into continuous, complete and
+non-overlapping segments.
 
-It does not extract facts, decisions, todos, questions or summaries.
+The script does not:
 
-Examples:
+- collect or merge topics,
+- identify resumed topics,
+- extract facts,
+- extract decisions,
+- extract todos,
+- summarize the discussion.
+
+Example:
     python src/meeting_lab/segmentation/segment_topics.py \
         samples/chunks/chunk_01_normalized.txt
-
-    python src/meeting_lab/segmentation/segment_topics.py \
-        samples/chunks/chunk_01_normalized.txt \
-        --model qwen3:8b \
-        --output experiments/topic-segmentation/chunk_01_topics.json
 """
 
 from __future__ import annotations
@@ -32,131 +35,209 @@ import requests
 
 DEFAULT_MODEL = "qwen3:8b"
 DEFAULT_ENDPOINT = "http://localhost:11434/api/generate"
+DEFAULT_TARGET_BLOCK_CHARS = 600
 
 
 SYSTEM_INSTRUCTION = """
-Du analysierst die thematische Struktur eines Meeting-Transkripts.
+Du analysierst den chronologischen Verlauf eines Meeting-Transkripts.
 
-Deine einzige Aufgabe ist die Themensegmentierung.
+Deine einzige Aufgabe ist es, Stellen zu erkennen, an denen das Gespräch
+inhaltlich zu einem anderen Thema wechselt.
 
-Du sollst erkennen:
+Du erhältst nummerierte Textblöcke.
 
-1. wann ein Thema beginnt,
-2. wann ein Thema endet,
-3. wann zu einem anderen Thema gewechselt wird,
-4. wann ein früheres Thema erneut aufgenommen wird.
+Gib ausschließlich die Nummern der Blöcke zurück, nach denen ein echter
+Themenwechsel stattfindet.
+
+Beispiel:
+
+Wenn die Blöcke 1 bis 4 ein Thema behandeln und mit Block 5 ein neues Thema
+beginnt, gib 4 als Grenze zurück.
 
 Regeln:
 
-1. Extrahiere keine Fakten.
-2. Extrahiere keine Aufgaben.
-3. Extrahiere keine Entscheidungen.
-4. Extrahiere keine offenen Fragen.
-5. Fasse die Diskussion nicht zusammen.
-6. Bewerte die Aussagen nicht.
-7. Erfinde keine Themen, die im Text nicht behandelt werden.
-8. Verwende möglichst kurze und sachliche Themenbezeichnungen.
-9. Jeder Block muss genau einem Thema zugeordnet werden.
-10. Mehrere direkt aufeinanderfolgende Blöcke desselben Themas bilden ein Segment.
-11. Wird ein früheres Thema später wieder aufgenommen, verwende dieselbe topic_id.
-12. Kleine Rückfragen oder kurze Ergänzungen bleiben beim aktuellen Thema,
-    sofern sie kein eigenständiges Thema eröffnen.
-13. Organisatorische Übergänge dürfen als eigenes Thema erfasst werden, wenn
-    sie einen erkennbaren Gesprächsabschnitt bilden.
-14. Gib ausschließlich gültiges JSON aus.
-15. Gib kein Markdown und keine Erläuterungen außerhalb des JSON aus.
+1. Gib nur echte inhaltliche Themenwechsel zurück.
+2. Kleine Rückfragen sind kein Themenwechsel.
+3. Kurze Ergänzungen sind kein Themenwechsel.
+4. Sprecherwechsel sind kein Themenwechsel.
+5. Zustimmung oder Ablehnung sind kein Themenwechsel.
+6. Eine kurze Abschweifung ist nur dann ein eigenes Segment, wenn sie einen
+   erkennbaren Gesprächsabschnitt bildet.
+7. Organisatorische Einleitungen oder Verabschiedungen dürfen eigene Segmente
+   bilden.
+8. Fasse keine Inhalte zusammen.
+9. Vergib keine Themenbezeichnungen.
+10. Extrahiere keine Fakten, Aufgaben, Entscheidungen oder Fragen.
+11. Die letzte Blocknummer darf nicht als Themenwechsel ausgegeben werden.
+12. Die Blocknummern müssen aufsteigend und eindeutig sein.
+13. Gib ausschließlich gültiges JSON aus.
+14. Gib kein Markdown und keine zusätzlichen Erläuterungen aus.
 """.strip()
 
 
-OUTPUT_SCHEMA = {
-    "topics": [
-        {
-            "topic_id": "topic_001",
-            "title": "Kurze sachliche Themenbezeichnung",
-            "segments": [
-                {
-                    "start_block": 1,
-                    "end_block": 5,
-                }
-            ],
+TOPIC_CHANGE_JSON_SCHEMA: dict[str, Any] = {
+    "type": "object",
+    "properties": {
+        "topic_changes": {
+            "type": "array",
+            "items": {
+                "type": "integer",
+                "minimum": 1,
+            },
         }
-    ]
+    },
+    "required": ["topic_changes"],
+    "additionalProperties": False,
 }
 
 
 def parse_args() -> argparse.Namespace:
     parser = argparse.ArgumentParser(
-        description="Segment a meeting transcript into discussion topics."
+        description=(
+            "Detect topic boundaries in a normalized meeting transcript."
+        )
     )
+
     parser.add_argument(
         "input_file",
         type=Path,
-        help="Normalized transcript or transcript chunk",
+        help="Normalized transcript file",
     )
+
     parser.add_argument(
         "-o",
         "--output",
         type=Path,
-        help="Output JSON file; default: <input>_topics.json",
+        help="Output JSON file; default: <input>_segments.json",
     )
+
     parser.add_argument(
         "--model",
         default=DEFAULT_MODEL,
         help=f"Ollama model name (default: {DEFAULT_MODEL})",
     )
+
     parser.add_argument(
         "--endpoint",
         default=DEFAULT_ENDPOINT,
         help=f"Ollama generate endpoint (default: {DEFAULT_ENDPOINT})",
     )
+
     parser.add_argument(
         "--timeout",
         type=int,
         default=1800,
         help="HTTP timeout in seconds (default: 1800)",
     )
+
     parser.add_argument(
         "--temperature",
         type=float,
         default=0.0,
         help="Sampling temperature (default: 0.0)",
     )
+
+    parser.add_argument(
+        "--target-block-chars",
+        type=int,
+        default=DEFAULT_TARGET_BLOCK_CHARS,
+        help=(
+            "Approximate size of analysis blocks in characters "
+            f"(default: {DEFAULT_TARGET_BLOCK_CHARS})"
+        ),
+    )
+
     return parser.parse_args()
 
 
-def split_into_blocks(text: str) -> list[str]:
+def split_into_blocks(
+    text: str,
+    target_chars: int = DEFAULT_TARGET_BLOCK_CHARS,
+) -> list[str]:
     """
-    Split a transcript into stable, numbered discussion blocks.
+    Combine short transcript utterances into larger analysis blocks.
 
-    Blank-line-separated paragraphs are preferred. If the transcript contains
-    no blank lines, individual non-empty lines are used as blocks.
+    Whisper-derived transcripts often contain one short utterance per
+    paragraph. Adjacent utterances are therefore grouped until the approximate
+    target size is reached.
     """
-    normalized = text.replace("\r\n", "\n").replace("\r", "\n").strip()
+    if target_chars < 1:
+        raise ValueError(
+            "target_chars must be greater than zero."
+        )
 
-    paragraphs = [
+    normalized = (
+        text.replace("\r\n", "\n")
+        .replace("\r", "\n")
+        .strip()
+    )
+
+    units = [
         part.strip()
         for part in re.split(r"\n\s*\n+", normalized)
         if part.strip()
     ]
 
-    if len(paragraphs) > 1:
-        return paragraphs
+    if not units:
+        units = [
+            line.strip()
+            for line in normalized.splitlines()
+            if line.strip()
+        ]
 
-    return [line.strip() for line in normalized.splitlines() if line.strip()]
+    blocks: list[str] = []
+    current_units: list[str] = []
+    current_length = 0
+
+    for unit in units:
+        separator_length = 1 if current_units else 0
+
+        projected_length = (
+            current_length
+            + separator_length
+            + len(unit)
+        )
+
+        if (
+            current_units
+            and projected_length > target_chars
+        ):
+            blocks.append("\n".join(current_units))
+
+            current_units = [unit]
+            current_length = len(unit)
+
+        else:
+            current_units.append(unit)
+            current_length = projected_length
+
+    if current_units:
+        blocks.append("\n".join(current_units))
+
+    return blocks
 
 
-def render_numbered_blocks(blocks: list[str]) -> str:
+def render_numbered_blocks(
+    blocks: list[str],
+) -> str:
     return "\n\n".join(
         f"[BLOCK {number}]\n{block}"
-        for number, block in enumerate(blocks, start=1)
+        for number, block in enumerate(
+            blocks,
+            start=1,
+        )
     )
 
 
-def build_prompt(source_name: str, blocks: list[str]) -> str:
-    schema_text = json.dumps(OUTPUT_SCHEMA, ensure_ascii=False, indent=2)
-    numbered_transcript = render_numbered_blocks(blocks)
+def build_prompt(
+    source_name: str,
+    blocks: list[str],
+) -> str:
+    numbered_transcript = render_numbered_blocks(
+        blocks
+    )
 
-    return f"""{SYSTEM_INSTRUCTION}
+    return f"""Bestimme die Stellen, an denen sich das Gesprächsthema ändert.
 
 Quelldatei:
 {source_name}
@@ -164,24 +245,19 @@ Quelldatei:
 Anzahl der Blöcke:
 {len(blocks)}
 
-Erwartete JSON-Struktur:
-{schema_text}
+Erwartete Ausgabe:
 
-Zusätzliche Anforderungen:
+{{
+  "topic_changes": [4, 12, 18]
+}}
 
-- Alle topic_id-Werte müssen dem Muster topic_001, topic_002 usw. folgen.
-- Die Nummerierung beginnt mit topic_001.
-- Die topic_id-Werte müssen innerhalb der Ausgabe eindeutig sein.
-- start_block und end_block beziehen sich auf die angegebenen Blocknummern.
-- start_block darf nicht größer als end_block sein.
-- Kein Block darf fehlen.
-- Kein Block darf mehreren Themen gleichzeitig zugeordnet werden.
-- Direkt aufeinanderfolgende Bereiche desselben Themas sollen als ein Segment
-  ausgegeben werden.
-- Nicht zusammenhängende Bereiche desselben Themas sollen als mehrere Segmente
-  innerhalb desselben Themas ausgegeben werden.
-- Themenbezeichnungen sollen knapp sein und keine Zusammenfassung enthalten.
-- Der Schlüssel "topics" muss immer vorhanden sein.
+Bedeutung:
+
+- Der Wert 4 bedeutet, dass nach Block 4 ein neues Thema beginnt.
+- Der Wert 12 bedeutet, dass nach Block 12 ein neues Thema beginnt.
+- Der letzte Block darf nicht in der Liste stehen.
+- Falls es keinen Themenwechsel gibt, gib eine leere Liste zurück.
+- Gib nur eindeutige, aufsteigend sortierte Blocknummern zurück.
 
 TRANSKRIPT:
 --- BEGINN TRANSKRIPT ---
@@ -199,20 +275,26 @@ def call_ollama(
 ) -> tuple[str, dict[str, Any]]:
     payload = {
         "model": model,
+        "system": SYSTEM_INSTRUCTION,
         "prompt": prompt,
         "stream": False,
-        "format": "json",
+        "format": TOPIC_CHANGE_JSON_SCHEMA,
+        "think": False,
         "options": {
             "temperature": temperature,
+            "seed": 42,
+            "num_ctx": 32768,
         },
     }
 
     started = time.perf_counter()
+
     response = requests.post(
         endpoint,
         json=payload,
         timeout=timeout,
     )
+
     elapsed = time.perf_counter() - started
 
     response.raise_for_status()
@@ -220,197 +302,226 @@ def call_ollama(
     data = response.json()
     response_text = data.get("response")
 
-    if not isinstance(response_text, str) or not response_text.strip():
-        raise ValueError("Ollama returned no usable response text.")
+    if (
+        not isinstance(response_text, str)
+        or not response_text.strip()
+    ):
+        raise ValueError(
+            "Ollama returned no usable response text."
+        )
 
     metadata = {
         "model": data.get("model", model),
-        "elapsed_seconds": round(elapsed, 3),
-        "total_duration_ns": data.get("total_duration"),
-        "load_duration_ns": data.get("load_duration"),
-        "prompt_eval_count": data.get("prompt_eval_count"),
-        "prompt_eval_duration_ns": data.get("prompt_eval_duration"),
-        "eval_count": data.get("eval_count"),
-        "eval_duration_ns": data.get("eval_duration"),
+        "elapsed_seconds": round(
+            elapsed,
+            3,
+        ),
+        "total_duration_ns": data.get(
+            "total_duration"
+        ),
+        "load_duration_ns": data.get(
+            "load_duration"
+        ),
+        "prompt_eval_count": data.get(
+            "prompt_eval_count"
+        ),
+        "prompt_eval_duration_ns": data.get(
+            "prompt_eval_duration"
+        ),
+        "eval_count": data.get(
+            "eval_count"
+        ),
+        "eval_duration_ns": data.get(
+            "eval_duration"
+        ),
     }
 
     return response_text.strip(), metadata
 
 
-def parse_json_response(text: str) -> dict[str, Any]:
+def parse_json_response(
+    text: str,
+) -> dict[str, Any]:
     try:
         parsed = json.loads(text)
+
     except json.JSONDecodeError:
-        # Fallback for models that wrap JSON in Markdown or add text around it.
-        match = re.search(r"\{.*\}", text, flags=re.DOTALL)
+        match = re.search(
+            r"\{.*\}",
+            text,
+            flags=re.DOTALL,
+        )
+
         if not match:
             raise
-        parsed = json.loads(match.group(0))
+
+        parsed = json.loads(
+            match.group(0)
+        )
 
     if not isinstance(parsed, dict):
         raise ValueError(
-            "The model response is valid JSON but not a JSON object."
+            "The model response is not a JSON object."
         )
 
     return parsed
 
 
-def validate_topic_id(topic_id: Any) -> str:
-    if not isinstance(topic_id, str):
-        raise ValueError("Every topic must contain a string topic_id.")
-
-    if not re.fullmatch(r"topic_\d{3}", topic_id):
-        raise ValueError(
-            f"Invalid topic_id {topic_id!r}; expected format topic_001."
-        )
-
-    return topic_id
-
-
-def validate_segment(
-    segment: Any,
-    topic_id: str,
-    block_count: int,
-) -> dict[str, int]:
-    if not isinstance(segment, dict):
-        raise ValueError(
-            f"Topic {topic_id} contains a segment that is not an object."
-        )
-
-    start_block = segment.get("start_block")
-    end_block = segment.get("end_block")
-
-    if not isinstance(start_block, int) or isinstance(start_block, bool):
-        raise ValueError(
-            f"Topic {topic_id} contains an invalid start_block."
-        )
-
-    if not isinstance(end_block, int) or isinstance(end_block, bool):
-        raise ValueError(
-            f"Topic {topic_id} contains an invalid end_block."
-        )
-
-    if start_block < 1 or end_block > block_count:
-        raise ValueError(
-            f"Topic {topic_id} references blocks outside 1..{block_count}."
-        )
-
-    if start_block > end_block:
-        raise ValueError(
-            f"Topic {topic_id} contains start_block > end_block."
-        )
-
-    return {
-        "start_block": start_block,
-        "end_block": end_block,
-    }
-
-
-def normalize_topics(
+def validate_topic_changes(
     result: dict[str, Any],
     block_count: int,
-) -> list[dict[str, Any]]:
-    raw_topics = result.get("topics")
+) -> list[int]:
+    raw_changes = result.get("topic_changes")
 
-    if not isinstance(raw_topics, list):
-        raise ValueError("Model output does not contain a topics list.")
+    if not isinstance(raw_changes, list):
+        raise ValueError(
+            "Model output does not contain "
+            "a topic_changes list."
+        )
 
-    topics: list[dict[str, Any]] = []
-    seen_topic_ids: set[str] = set()
+    changes: list[int] = []
 
-    for raw_topic in raw_topics:
-        if not isinstance(raw_topic, dict):
-            raise ValueError("Every topic must be a JSON object.")
+    for value in raw_changes:
+        if (
+            not isinstance(value, int)
+            or isinstance(value, bool)
+        ):
+            raise ValueError(
+                "Every topic change must be "
+                "an integer block number."
+            )
 
-        topic_id = validate_topic_id(raw_topic.get("topic_id"))
+        if value < 1:
+            raise ValueError(
+                f"Invalid topic change: {value}"
+            )
 
-        if topic_id in seen_topic_ids:
-            raise ValueError(f"Duplicate topic_id: {topic_id}")
-        seen_topic_ids.add(topic_id)
+        if value >= block_count:
+            raise ValueError(
+                f"Topic change {value} is invalid. "
+                f"The last block is {block_count}."
+            )
 
-        title = raw_topic.get("title")
-        if not isinstance(title, str) or not title.strip():
-            raise ValueError(f"Topic {topic_id} has no usable title.")
+        changes.append(value)
 
-        raw_segments = raw_topic.get("segments")
-        if not isinstance(raw_segments, list) or not raw_segments:
-            raise ValueError(f"Topic {topic_id} has no segments.")
+    if len(changes) != len(set(changes)):
+        raise ValueError(
+            "The model returned duplicate "
+            "topic changes."
+        )
 
-        segments = [
-            validate_segment(segment, topic_id, block_count)
-            for segment in raw_segments
-        ]
-        segments.sort(key=lambda item: item["start_block"])
+    if changes != sorted(changes):
+        raise ValueError(
+            "The topic changes are not "
+            "sorted in ascending order."
+        )
 
-        topics.append(
+    return changes
+
+
+def build_segments(
+    topic_changes: list[int],
+    block_count: int,
+) -> list[dict[str, int | str]]:
+    """
+    Convert topic boundaries into continuous and non-overlapping segments.
+    """
+    segments: list[dict[str, int | str]] = []
+
+    start_block = 1
+
+    for number, end_block in enumerate(
+        topic_changes,
+        start=1,
+    ):
+        segments.append(
             {
-                "topic_id": topic_id,
-                "title": title.strip(),
-                "segments": segments,
+                "segment_id": (
+                    f"segment_{number:03d}"
+                ),
+                "start_block": start_block,
+                "end_block": end_block,
             }
         )
 
-    if not topics:
-        raise ValueError("The model returned no topics.")
+        start_block = end_block + 1
 
-    topics.sort(
-        key=lambda topic: min(
-            segment["start_block"] for segment in topic["segments"]
-        )
+    final_number = len(segments) + 1
+
+    segments.append(
+        {
+            "segment_id": (
+                f"segment_{final_number:03d}"
+            ),
+            "start_block": start_block,
+            "end_block": block_count,
+        }
     )
 
-    return topics
+    return segments
 
 
-def validate_block_coverage(
-    topics: list[dict[str, Any]],
+def validate_segments(
+    segments: list[dict[str, int | str]],
     block_count: int,
 ) -> None:
-    assignments: dict[int, str] = {}
-
-    for topic in topics:
-        topic_id = topic["topic_id"]
-
-        for segment in topic["segments"]:
-            for block_number in range(
-                segment["start_block"],
-                segment["end_block"] + 1,
-            ):
-                previous_topic = assignments.get(block_number)
-
-                if previous_topic is not None:
-                    raise ValueError(
-                        f"Block {block_number} is assigned to both "
-                        f"{previous_topic} and {topic_id}."
-                    )
-
-                assignments[block_number] = topic_id
-
-    missing_blocks = [
-        block_number
-        for block_number in range(1, block_count + 1)
-        if block_number not in assignments
-    ]
-
-    if missing_blocks:
-        formatted = ", ".join(str(number) for number in missing_blocks)
+    if not segments:
         raise ValueError(
-            f"The following blocks were not assigned to a topic: {formatted}"
+            "No segments were created."
+        )
+
+    expected_start = 1
+
+    for segment in segments:
+        start_block = segment["start_block"]
+        end_block = segment["end_block"]
+
+        if not isinstance(start_block, int):
+            raise ValueError(
+                "Invalid segment start block."
+            )
+
+        if not isinstance(end_block, int):
+            raise ValueError(
+                "Invalid segment end block."
+            )
+
+        if start_block != expected_start:
+            raise ValueError(
+                "Segments are not continuous."
+            )
+
+        if end_block < start_block:
+            raise ValueError(
+                "A segment ends before it starts."
+            )
+
+        expected_start = end_block + 1
+
+    if expected_start != block_count + 1:
+        raise ValueError(
+            "Segments do not cover all blocks."
         )
 
 
 def build_output(
     source_name: str,
     blocks: list[str],
-    topics: list[dict[str, Any]],
+    topic_changes: list[int],
+    segments: list[dict[str, int | str]],
     metadata: dict[str, Any],
+    target_block_chars: int,
 ) -> dict[str, Any]:
     return {
         "source": {
             "file": source_name,
             "block_count": len(blocks),
+            "target_block_chars": (
+                target_block_chars
+            ),
         },
-        "topics": topics,
+        "topic_changes": topic_changes,
+        "segments": segments,
         "_run": metadata,
     }
 
@@ -419,8 +530,15 @@ def write_raw_response(
     output_path: Path,
     raw_text: str,
 ) -> Path:
-    raw_path = output_path.with_suffix(".raw.txt")
-    raw_path.write_text(raw_text + "\n", encoding="utf-8")
+    raw_path = output_path.with_suffix(
+        ".raw.txt"
+    )
+
+    raw_path.write_text(
+        raw_text + "\n",
+        encoding="utf-8",
+    )
+
     return raw_path
 
 
@@ -430,7 +548,8 @@ def main() -> int:
     try:
         if not args.input_file.is_file():
             raise FileNotFoundError(
-                f"Input file not found: {args.input_file}"
+                f"Input file not found: "
+                f"{args.input_file}"
             )
 
         transcript = args.input_file.read_text(
@@ -438,28 +557,50 @@ def main() -> int:
         ).strip()
 
         if not transcript:
-            raise ValueError("The input file is empty.")
+            raise ValueError(
+                "The input file is empty."
+            )
 
-        blocks = split_into_blocks(transcript)
+        blocks = split_into_blocks(
+            transcript,
+            target_chars=(
+                args.target_block_chars
+            ),
+        )
 
         if not blocks:
-            raise ValueError("No discussion blocks could be created.")
+            raise ValueError(
+                "No analysis blocks could "
+                "be created."
+            )
 
-        output_path = args.output or args.input_file.with_name(
-            f"{args.input_file.stem}_topics.json"
+        output_path = (
+            args.output
+            or args.input_file.with_name(
+                f"{args.input_file.stem}"
+                "_segments.json"
+            )
+        )
+
+        output_path.parent.mkdir(
+            parents=True,
+            exist_ok=True,
         )
-        output_path.parent.mkdir(parents=True, exist_ok=True)
 
         prompt = build_prompt(
             source_name=args.input_file.name,
             blocks=blocks,
         )
 
-        print(f"Model:   {args.model}")
-        print(f"Input:   {args.input_file}")
-        print(f"Blocks:  {len(blocks)}")
-        print(f"Output:  {output_path}")
-        print("Segmenting discussion topics ...")
+        print(f"Model:        {args.model}")
+        print(f"Input:        {args.input_file}")
+        print(f"Blocks:       {len(blocks)}")
+        print(
+            "Block target: "
+            f"{args.target_block_chars} characters"
+        )
+        print(f"Output:       {output_path}")
+        print("Detecting topic boundaries ...")
 
         raw_text, metadata = call_ollama(
             endpoint=args.endpoint,
@@ -470,28 +611,53 @@ def main() -> int:
         )
 
         try:
-            parsed = parse_json_response(raw_text)
-            topics = normalize_topics(
-                result=parsed,
+            parsed = parse_json_response(
+                raw_text
+            )
+
+            topic_changes = (
+                validate_topic_changes(
+                    result=parsed,
+                    block_count=len(blocks),
+                )
+            )
+
+            segments = build_segments(
+                topic_changes=topic_changes,
                 block_count=len(blocks),
             )
-            validate_block_coverage(
-                topics=topics,
+
+            validate_segments(
+                segments=segments,
                 block_count=len(blocks),
             )
-        except (json.JSONDecodeError, ValueError) as exc:
-            raw_path = write_raw_response(output_path, raw_text)
+
+        except (
+            json.JSONDecodeError,
+            ValueError,
+        ) as exc:
+            raw_path = write_raw_response(
+                output_path,
+                raw_text,
+            )
+
             raise ValueError(
-                f"Model output could not be validated. "
-                f"Raw output saved to: {raw_path}. "
+                "Model output could not be "
+                "validated. "
+                f"Raw output saved to: "
+                f"{raw_path}. "
                 f"Reason: {exc}"
             ) from exc
 
         result = build_output(
             source_name=args.input_file.name,
             blocks=blocks,
-            topics=topics,
+            topic_changes=topic_changes,
+            segments=segments,
             metadata=metadata,
+            target_block_chars=(
+                args.target_block_chars
+            ),
         )
 
         output_path.write_text(
@@ -504,40 +670,54 @@ def main() -> int:
             encoding="utf-8",
         )
 
-        segment_count = sum(
-            len(topic["segments"]) for topic in topics
+        print(
+            f"Done in "
+            f"{metadata['elapsed_seconds']:.1f} "
+            "seconds."
         )
-        resumed_topic_count = sum(
-            1 for topic in topics if len(topic["segments"]) > 1
+        print(
+            f"Topic changes:  "
+            f"{len(topic_changes)}"
+        )
+        print(
+            f"Segments:       "
+            f"{len(segments)}"
         )
-
-        print(f"Done in {metadata['elapsed_seconds']:.1f} seconds.")
-        print(f"Topics:          {len(topics)}")
-        print(f"Segments:        {segment_count}")
-        print(f"Resumed topics:  {resumed_topic_count}")
 
         return 0
 
     except requests.ConnectionError:
         print(
-            "Error: Ollama is not reachable. Is `ollama serve` running?",
+            "Error: Ollama is not reachable. "
+            "Is `ollama serve` running?",
             file=sys.stderr,
         )
         return 1
+
     except requests.Timeout:
         print(
             "Error: The Ollama request timed out.",
             file=sys.stderr,
         )
         return 1
+
     except requests.HTTPError as exc:
         print(
-            f"Error: Ollama returned an HTTP error: {exc}",
+            "Error: Ollama returned an HTTP "
+            f"error: {exc}",
             file=sys.stderr,
         )
         return 1
-    except (OSError, UnicodeError, ValueError) as exc:
-        print(f"Error: {exc}", file=sys.stderr)
+
+    except (
+        OSError,
+        UnicodeError,
+        ValueError,
+    ) as exc:
+        print(
+            f"Error: {exc}",
+            file=sys.stderr,
+        )
         return 1