fix: prevent panics in robot-mode JSON output and arithmetic paths

Peer code review found multiple panic-reachable paths:

1. serde_json::to_string().unwrap() in 4 robot-mode output functions
   (who.rs, main.rs x3). If serialization ever failed (e.g., NaN from
   edge-case division), the CLI would panic with an unhelpful stack trace.
   Replaced with unwrap_or_else that emits a structured JSON error fallback.

2. encode_rowid() in chunk_ids.rs used unchecked multiplication
   (document_id * 1000). On extreme document IDs this could silently wrap
   in release mode, causing embedding rowid collisions. Now uses
   checked_mul + checked_add with a diagnostic panic message.

3. HTTP response body truncation at byte index 500 in client.rs could
   split a multi-byte UTF-8 character, causing a panic. Now uses
   floor_char_boundary(500) for safe truncation.

4. who.rs reviews mode: SQL used `m.author_username != ?1` which silently
   dropped MRs with NULL author_username (SQL NULL != anything = NULL).
   Changed to `(m.author_username IS NULL OR m.author_username != ?1)`
   to match the pattern already used in expert mode.

5. handle_auth_test hardcoded exit code 5 for all errors regardless of
   type. Config not found (20), token not set (4), and network errors (8)
   all incorrectly returned 5. Now uses e.exit_code() from the actual
   LoreError, with proper suggestion hints in human mode.

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

src/cli/commands/who.rs

@@ -851,7 +851,7 @@ fn query_reviews(
          WHERE n.author_username = ?1
            AND n.note_type = 'DiffNote'
            AND n.is_system = 0
-           AND m.author_username != ?1
+           AND (m.author_username IS NULL OR m.author_username != ?1)
            AND n.created_at >= ?2
            AND (?3 IS NULL OR n.project_id = ?3)";
 
@@ -868,7 +868,7 @@ fn query_reviews(
          WHERE n.author_username = ?1
            AND n.note_type = 'DiffNote'
            AND n.is_system = 0
-           AND m.author_username != ?1
+           AND (m.author_username IS NULL OR m.author_username != ?1)
            AND n.created_at >= ?2
            AND (?3 IS NULL OR n.project_id = ?3)";
 
@@ -888,7 +888,7 @@ fn query_reviews(
          WHERE n.author_username = ?1
            AND n.note_type = 'DiffNote'
            AND n.is_system = 0
-           AND m.author_username != ?1
+           AND (m.author_username IS NULL OR m.author_username != ?1)
            AND ltrim(n.body) LIKE '**%**%'
            AND n.created_at >= ?2
            AND (?3 IS NULL OR n.project_id = ?3)
@@ -1798,7 +1798,12 @@ pub fn print_who_json(run: &WhoRun, args: &WhoArgs, elapsed_ms: u64) {
         meta: RobotMeta { elapsed_ms },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    println!(
+        "{}",
+        serde_json::to_string(&output).unwrap_or_else(|e| {
+            format!(r#"{{"ok":false,"error":{{"code":"INTERNAL_ERROR","message":"JSON serialization failed: {e}"}}}}"#)
+        })
+    );
 }
 
 #[derive(Serialize)]

src/embedding/chunk_ids.rs

@@ -1,7 +1,12 @@
 pub const CHUNK_ROWID_MULTIPLIER: i64 = 1000;
 
 pub fn encode_rowid(document_id: i64, chunk_index: i64) -> i64 {
-    document_id * CHUNK_ROWID_MULTIPLIER + chunk_index
+    document_id
+        .checked_mul(CHUNK_ROWID_MULTIPLIER)
+        .and_then(|v| v.checked_add(chunk_index))
+        .unwrap_or_else(|| {
+            panic!("encode_rowid overflow: document_id={document_id}, chunk_index={chunk_index}")
+        })
 }
 
 pub fn decode_rowid(rowid: i64) -> (i64, i64) {

src/gitlab/client.rs

@@ -70,15 +70,19 @@ impl GitLabClient {
         headers.insert(ACCEPT, HeaderValue::from_static("application/json"));
 
         let client = Client::builder()
-            .default_headers(headers)
+            .default_headers(headers.clone())
             .timeout(Duration::from_secs(30))
             .build()
             .unwrap_or_else(|e| {
                 warn!(
                     error = %e,
-                    "Failed to build configured HTTP client; falling back to default client"
+                    "Failed to build configured HTTP client; falling back to default client with timeout"
                 );
-                Client::new()
+                Client::builder()
+                    .default_headers(headers)
+                    .timeout(Duration::from_secs(30))
+                    .build()
+                    .unwrap_or_else(|_| Client::new())
             });
 
         Self {
@@ -180,7 +184,7 @@ impl GitLabClient {
                 let text = response.text().await?;
                 serde_json::from_str(&text).map_err(|e| {
                     let preview = if text.len() > 500 {
-                        &text[..500]
+                        &text[..text.floor_char_boundary(500)]
                     } else {
                         &text
                     };

src/main.rs

@@ -845,7 +845,12 @@ fn print_combined_ingest_json(
         meta: RobotMeta { elapsed_ms },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    println!(
+        "{}",
+        serde_json::to_string(&output).unwrap_or_else(|e| {
+            format!(r#"{{"ok":false,"error":{{"code":"INTERNAL_ERROR","message":"JSON serialization failed: {e}"}}}}"#)
+        })
+    );
 }
 
 #[derive(Serialize)]
@@ -874,7 +879,12 @@ fn print_combined_dry_run_json(
         },
     };
 
-    println!("{}", serde_json::to_string(&output).unwrap());
+    println!(
+        "{}",
+        serde_json::to_string(&output).unwrap_or_else(|e| {
+            format!(r#"{{"ok":false,"error":{{"code":"INTERNAL_ERROR","message":"JSON serialization failed: {e}"}}}}"#)
+        })
+    );
 }
 
 async fn handle_count(
@@ -966,7 +976,12 @@ fn print_init_json(result: &InitResult) {
                 .collect(),
         },
     };
-    println!("{}", serde_json::to_string(&output).unwrap());
+    println!(
+        "{}",
+        serde_json::to_string(&output).unwrap_or_else(|e| {
+            format!(r#"{{"ok":false,"error":{{"code":"INTERNAL_ERROR","message":"JSON serialization failed: {e}"}}}}"#)
+        })
+    );
 }
 
 async fn handle_init(
@@ -1198,17 +1213,20 @@ async fn handle_auth_test(
         }
         Err(e) => {
             if robot_mode {
-                let output = FallbackErrorOutput {
+                let output = RobotErrorOutput::from(&e);
-                    error: FallbackError {
+                eprintln!(
-                        code: "AUTH_FAILED".to_string(),
+                    "{}",
-                        message: e.to_string(),
+                    serde_json::to_string(&output).unwrap_or_else(|_| {
-                    },
+                        format!(r#"{{"error":{{"code":"{}","message":"{}"}}}}"#, e.code(), e)
-                };
+                    })
-                eprintln!("{}", serde_json::to_string(&output)?);
+                );
             } else {
-                eprintln!("{}", style(format!("Error: {e}")).red());
+                eprintln!("{} {}", style("Error:").red(), e);
+                if let Some(suggestion) = e.suggestion() {
+                    eprintln!("{} {}", style("Hint:").yellow(), suggestion);
+                }
             }
-            std::process::exit(5);
+            std::process::exit(e.exit_code());
         }
     }
 }