fix: Inflate LLM token estimates and forward max_tokens on retry

Stage 4 classification was truncating (finish=length) because the 0.15x
output ratio underestimated token needs. Inflated all stage ratios,
bumped the buffer from 20% to 50%, raised the floor from 2048 to 4096,
and fixed _safe_parse_llm_response to forward max_tokens on retry
instead of falling back to the 65k default.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/pipeline/llm_client.py

@@ -59,14 +59,14 @@ def strip_think_tags(text: str) -> str:
 # Stage-specific output multipliers: estimated output tokens as a ratio of input tokens.
 # These are empirically tuned based on observed pipeline behavior.
 _STAGE_OUTPUT_RATIOS: dict[str, float] = {
-    "stage2_segmentation": 0.3,    # Compact topic groups — much smaller than input
+    "stage2_segmentation": 0.6,    # Compact topic groups — smaller than input
-    "stage3_extraction": 1.2,      # Detailed moments with summaries — can exceed input
+    "stage3_extraction": 2.0,      # Detailed moments with summaries — can well exceed input
-    "stage4_classification": 0.15,  # Index + category + tags per moment — very compact
+    "stage4_classification": 0.5,  # Index + category + tags per moment — small but varies
-    "stage5_synthesis": 1.5,       # Full prose technique pages — heaviest output
+    "stage5_synthesis": 2.5,       # Full prose technique pages — heaviest output
 }
 
 # Minimum floor so we never send a trivially small max_tokens
-_MIN_MAX_TOKENS = 2048
+_MIN_MAX_TOKENS = 4096
 
 
 def estimate_tokens(text: str) -> int:
@@ -111,8 +111,8 @@ def estimate_max_tokens(
     ratio = _STAGE_OUTPUT_RATIOS.get(stage or "", 1.0)
     estimated_output = int(input_tokens * ratio)
 
-    # Add a 20% buffer for JSON overhead and variability
+    # Add a 50% buffer for JSON overhead and variability
-    estimated_output = int(estimated_output * 1.2)
+    estimated_output = int(estimated_output * 1.5)
 
     # Clamp to [_MIN_MAX_TOKENS, hard_limit]
     result = max(_MIN_MAX_TOKENS, min(estimated_output, hard_limit))

backend/pipeline/stages.py

@@ -263,6 +263,7 @@ def _safe_parse_llm_response(
     user_prompt: str,
     modality: str = "chat",
     model_override: str | None = None,
+    max_tokens: int | None = None,
 ):
     """Parse LLM response with one retry on failure.
 
@@ -284,6 +285,7 @@ def _safe_parse_llm_response(
         retry_raw = llm.complete(
             system_prompt, nudge_prompt, response_model=model_cls,
             modality=modality, model_override=model_override,
+            max_tokens=max_tokens,
         )
         return llm.parse_response(retry_raw, model_cls)
 
@@ -340,7 +342,7 @@ def stage2_segmentation(self, video_id: str, run_id: str | None = None) -> str:
         raw = llm.complete(system_prompt, user_prompt, response_model=SegmentationResult, on_complete=_make_llm_callback(video_id, "stage2_segmentation", system_prompt=system_prompt, user_prompt=user_prompt, run_id=run_id),
                            modality=modality, model_override=model_override, max_tokens=max_tokens)
         result = _safe_parse_llm_response(raw, SegmentationResult, llm, system_prompt, user_prompt,
-                                          modality=modality, model_override=model_override)
+                                          modality=modality, model_override=model_override, max_tokens=max_tokens)
 
         # Update topic_label on each segment row
         seg_by_index = {s.segment_index: s for s in segments}
@@ -432,7 +434,7 @@ def stage3_extraction(self, video_id: str, run_id: str | None = None) -> str:
             raw = llm.complete(system_prompt, user_prompt, response_model=ExtractionResult, on_complete=_make_llm_callback(video_id, "stage3_extraction", system_prompt=system_prompt, user_prompt=user_prompt, run_id=run_id, context_label=topic_label),
                                modality=modality, model_override=model_override, max_tokens=max_tokens)
             result = _safe_parse_llm_response(raw, ExtractionResult, llm, system_prompt, user_prompt,
-                                              modality=modality, model_override=model_override)
+                                              modality=modality, model_override=model_override, max_tokens=max_tokens)
 
             # Create KeyMoment rows
             for moment in result.moments:
@@ -541,7 +543,7 @@ def stage4_classification(self, video_id: str, run_id: str | None = None) -> str
         raw = llm.complete(system_prompt, user_prompt, response_model=ClassificationResult, on_complete=_make_llm_callback(video_id, "stage4_classification", system_prompt=system_prompt, user_prompt=user_prompt, run_id=run_id),
                            modality=modality, model_override=model_override, max_tokens=max_tokens)
         result = _safe_parse_llm_response(raw, ClassificationResult, llm, system_prompt, user_prompt,
-                                          modality=modality, model_override=model_override)
+                                          modality=modality, model_override=model_override, max_tokens=max_tokens)
 
         # Apply content_type overrides and prepare classification data for stage 5
         classification_data = []
@@ -786,7 +788,7 @@ def stage5_synthesis(self, video_id: str, run_id: str | None = None) -> str:
             raw = llm.complete(system_prompt, user_prompt, response_model=SynthesisResult, on_complete=_make_llm_callback(video_id, "stage5_synthesis", system_prompt=system_prompt, user_prompt=user_prompt, run_id=run_id, context_label=category),
                                modality=modality, model_override=model_override, max_tokens=max_tokens)
             result = _safe_parse_llm_response(raw, SynthesisResult, llm, system_prompt, user_prompt,
-                                              modality=modality, model_override=model_override)
+                                              modality=modality, model_override=model_override, max_tokens=max_tokens)
 
             # Load prior pages from this video (snapshot taken before pipeline reset)
             prior_page_ids = _load_prior_pages(video_id)