fix(robot): replace JSON serialization unwrap with graceful error handling

Replace serde_json::to_string(&output).unwrap() with match-based error
handling across all robot-mode JSON printers. On serialization failure,
the error is now written to stderr instead of panicking. This hardens
the CLI against unexpected Serialize failures in production.

Affected commands: count (2), embed, generate-docs, ingest (2), search,
stats, sync (2), sync-status, timeline.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/commands/count.rs

@@ -257,7 +257,10 @@ pub fn print_event_count_json(counts: &EventCounts, elapsed_ms: u64) {
         meta: RobotMeta { elapsed_ms },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 pub fn print_event_count(counts: &EventCounts) {
@@ -325,7 +328,10 @@ pub fn print_count_json(result: &CountResult, elapsed_ms: u64) {
         meta: RobotMeta { elapsed_ms },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 pub fn print_count(result: &CountResult) {

src/cli/commands/embed.rs

@@ -137,5 +137,8 @@ pub fn print_embed_json(result: &EmbedCommandResult, elapsed_ms: u64) {
         data: result,
         meta: RobotMeta { elapsed_ms },
     };
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }

src/cli/commands/generate_docs.rs

@@ -259,7 +259,10 @@ pub fn print_generate_docs_json(result: &GenerateDocsResult, elapsed_ms: u64) {
         },
         meta: RobotMeta { elapsed_ms },
     };
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 #[cfg(test)]

src/cli/commands/ingest.rs

@@ -982,7 +982,10 @@ pub fn print_ingest_summary_json(result: &IngestResult, elapsed_ms: u64) {
         meta: RobotMeta { elapsed_ms },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 pub fn print_ingest_summary(result: &IngestResult) {
@@ -1109,5 +1112,8 @@ pub fn print_dry_run_preview_json(preview: &DryRunPreview) {
         data: preview.clone(),
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }

src/cli/commands/search.rs

@@ -439,5 +439,8 @@ pub fn print_search_results_json(
         let expanded = crate::cli::robot::expand_fields_preset(f, "search");
         crate::cli::robot::filter_fields(&mut value, "results", &expanded);
     }
-    println!("{}", serde_json::to_string(&value).unwrap());
+    match serde_json::to_string(&value) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }

src/cli/commands/stats.rs

@@ -585,5 +585,8 @@ pub fn print_stats_json(result: &StatsResult, elapsed_ms: u64) {
         },
         meta: RobotMeta { elapsed_ms },
     };
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }

src/cli/commands/sync.rs

@@ -746,7 +746,10 @@ pub fn print_sync_json(result: &SyncResult, elapsed_ms: u64, metrics: Option<&Me
             stages,
         },
     };
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 #[derive(Debug, Default, Serialize)]
@@ -880,7 +883,10 @@ pub fn print_sync_dry_run_json(result: &SyncDryRunResult) {
         },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 #[cfg(test)]

src/cli/commands/sync_status.rs

@@ -268,7 +268,10 @@ pub fn print_sync_status_json(result: &SyncStatusResult, elapsed_ms: u64) {
         meta: RobotMeta { elapsed_ms },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    match serde_json::to_string(&output) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 pub fn print_sync_status(result: &SyncStatusResult) {

src/cli/commands/timeline.rs

@@ -374,7 +374,10 @@ pub fn print_timeline_json_with_meta(
         let expanded = crate::cli::robot::expand_fields_preset(f, "timeline");
         crate::cli::robot::filter_fields(&mut value, "events", &expanded);
     }
-    println!("{}", serde_json::to_string(&value).unwrap());
+    match serde_json::to_string(&value) {
+        Ok(json) => println!("{json}"),
+        Err(e) => eprintln!("Error serializing to JSON: {e}"),
+    }
 }
 
 #[derive(Serialize)]