Fix EvidenceSynthesizer callback signature mismatch

The EvidenceSynthesizer expects callback(message, current, total) with 3 args
but the agent callback is callback(event, data) with 2 args. This caused:
"takes 3 positional arguments but 4 were given"

Fix:
- Add _make_synthesis_callback() wrapper method to convert between formats
- Emits "synthesis_progress" events with "X/Y | message" format
- Update all 4 locations passing progress_callback to EvidenceSynthesizer
- Add synthesis_progress to GUI progress map (87%)
- Add activity log formatting with 📝 icon

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: hherb

src/bmlibrarian/agents/systematic_review/agent.py

@@ -1295,7 +1295,7 @@ def run_review(
                     temperature=self.config.synthesis_temperature,
                     citation_min_relevance=self.config.citation_min_relevance,
                     max_citations_per_paper=self.config.max_citations_per_paper,
-                    progress_callback=self.callback,
+                    progress_callback=self._make_synthesis_callback(),
                 )
 
                 with self.documenter.log_step_with_timer(

src/bmlibrarian/agents/systematic_review/resume_mixin.py

@@ -97,6 +97,25 @@ class CheckpointResumeMixin:
         - get_below_threshold_papers(): Get below threshold papers
     """
 
+    def _make_synthesis_callback(self) -> Optional[Callable[[str, int, int], None]]:
+        """
+        Create a callback wrapper for EvidenceSynthesizer.
+
+        The synthesizer expects callback(message, current, total) but the agent
+        callback is callback(event, data). This wrapper converts between the two.
+
+        Returns:
+            Wrapped callback or None if no callback is set.
+        """
+        if not self.callback:
+            return None
+
+        def synthesis_callback(message: str, current: int, total: int) -> None:
+            # Convert to agent callback format: (event, data)
+            self.callback("synthesis_progress", f"{current}/{total} | {message}")
+
+        return synthesis_callback
+
     def run_review_from_checkpoint(
         self,
         checkpoint_path: str,
@@ -821,7 +840,7 @@ def _continue_from_quality_assessment(
                 temperature=self.config.synthesis_temperature,
                 citation_min_relevance=self.config.citation_min_relevance,
                 max_citations_per_paper=self.config.max_citations_per_paper,
-                progress_callback=self.callback,
+                progress_callback=self._make_synthesis_callback(),
             )
 
             with self.documenter.log_step_with_timer(
@@ -1016,7 +1035,7 @@ def _continue_from_composite_scoring(
                 temperature=self.config.synthesis_temperature,
                 citation_min_relevance=self.config.citation_min_relevance,
                 max_citations_per_paper=self.config.max_citations_per_paper,
-                progress_callback=self.callback,
+                progress_callback=self._make_synthesis_callback(),
             )
 
             with self.documenter.log_step_with_timer(
@@ -1360,7 +1379,7 @@ def _continue_from_scoring_phase(
                 temperature=self.config.synthesis_temperature,
                 citation_min_relevance=self.config.citation_min_relevance,
                 max_citations_per_paper=self.config.max_citations_per_paper,
-                progress_callback=self.callback,
+                progress_callback=self._make_synthesis_callback(),
             )
 
             with self.documenter.log_step_with_timer(

src/bmlibrarian/gui/qt/plugins/systematic_review/systematic_review_tab.py

@@ -252,6 +252,7 @@ def _progress_callback(self, event: str, data: str) -> None:
             "quality_progress": 80,
             "quality_complete": 85,
             "quality_assessment_completed": 85,
+            "synthesis_progress": 87,
             "reporting_started": 90,
             "reporting_complete": 95,
         }
@@ -327,6 +328,12 @@ def _format_activity_entry(self, event: str, data: str) -> Optional[str]:
             return f"**[{timestamp}]** {data}\n"
         elif event == "quality_complete" or event == "quality_assessment_completed":
             return f"**[{timestamp}]** ✓ Quality assessment complete: {data}\n\n---\n"
+        elif event == "synthesis_progress":
+            # Format: "X/Y | message" - extract the meaningful part
+            if " | " in data:
+                _, info = data.split(" | ", 1)
+                return f"**[{timestamp}]** 📝 {info}\n"
+            return f"**[{timestamp}]** 📝 {data}\n"
         elif event == "reporting_started":
             return f"**[{timestamp}]** Generating report...\n"
         elif event == "reporting_complete":