fix: resolve all 301 error handling anti-patterns across codebase

Systematic cleanup of every error handling anti-pattern detected by the
automated scanner. 289 issues fixed via code changes, 12 approved with
specific technical justifications.

Changes across 90 files:
- GENERIC_CATCH (141): Added instanceof Error type discrimination
- LARGE_TRY_BLOCK (82): Extracted helper methods to narrow try scope to ≤10 lines
- NO_LOGGING_IN_CATCH (65): Added logger/console calls for error visibility
- CATCH_AND_CONTINUE_CRITICAL_PATH (10): Added throw/return or approved overrides
- ERROR_STRING_MATCHING (2): Approved with rationale (no typed error classes)
- ERROR_MESSAGE_GUESSING (1): Replaced chained .includes() with documented pattern array
- PROMISE_CATCH_NO_LOGGING (1): Added logging to .catch() handler

Also fixes a detector bug where nested try/catch inside a catch block
corrupted brace-depth tracking, causing false positives.

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

src/supervisor/shutdown.ts

@@ -35,11 +35,19 @@ export async function runShutdownCascade(options: ShutdownCascadeOptions): Promi
 
     try {
       await signalProcess(record.pid, 'SIGTERM');
-    } catch (error) {
-      logger.debug('SYSTEM', 'Failed to send SIGTERM to child process', {
-        pid: record.pid,
-        type: record.type
-      }, error as Error);
+    } catch (error: unknown) {
+      if (error instanceof Error) {
+        logger.debug('SYSTEM', 'Failed to send SIGTERM to child process', {
+          pid: record.pid,
+          type: record.type
+        }, error);
+      } else {
+        logger.warn('SYSTEM', 'Failed to send SIGTERM to child process (non-Error)', {
+          pid: record.pid,
+          type: record.type,
+          error: String(error)
+        });
+      }
     }
   }
 
@@ -49,11 +57,19 @@ export async function runShutdownCascade(options: ShutdownCascadeOptions): Promi
   for (const record of survivors) {
     try {
       await signalProcess(record.pid, 'SIGKILL');
-    } catch (error) {
-      logger.debug('SYSTEM', 'Failed to force kill child process', {
-        pid: record.pid,
-        type: record.type
-      }, error as Error);
+    } catch (error: unknown) {
+      if (error instanceof Error) {
+        logger.debug('SYSTEM', 'Failed to force kill child process', {
+          pid: record.pid,
+          type: record.type
+        }, error);
+      } else {
+        logger.warn('SYSTEM', 'Failed to force kill child process (non-Error)', {
+          pid: record.pid,
+          type: record.type,
+          error: String(error)
+        });
+      }
     }
   }
 
@@ -68,8 +84,15 @@ export async function runShutdownCascade(options: ShutdownCascadeOptions): Promi
 
   try {
     rmSync(pidFilePath, { force: true });
-  } catch (error) {
-    logger.debug('SYSTEM', 'Failed to remove PID file during shutdown', { pidFilePath }, error as Error);
+  } catch (error: unknown) {
+    if (error instanceof Error) {
+      logger.debug('SYSTEM', 'Failed to remove PID file during shutdown', { pidFilePath }, error);
+    } else {
+      logger.warn('SYSTEM', 'Failed to remove PID file during shutdown (non-Error)', {
+        pidFilePath,
+        error: String(error)
+      });
+    }
   }
 
   options.registry.pruneDeadEntries();
@@ -91,10 +114,12 @@ async function signalProcess(pid: number, signal: 'SIGTERM' | 'SIGKILL'): Promis
   if (signal === 'SIGTERM') {
     try {
       process.kill(pid, signal);
-    } catch (error) {
-      const errno = (error as NodeJS.ErrnoException).code;
-      if (errno === 'ESRCH') {
-        return;
+    } catch (error: unknown) {
+      if (error instanceof Error) {
+        const errno = (error as NodeJS.ErrnoException).code;
+        if (errno === 'ESRCH') {
+          return;
+        }
       }
       throw error;
     }
@@ -136,10 +161,12 @@ async function signalProcess(pid: number, signal: 'SIGTERM' | 'SIGKILL'): Promis
 
   try {
     process.kill(pid, signal);
-  } catch (error) {
-    const errno = (error as NodeJS.ErrnoException).code;
-    if (errno === 'ESRCH') {
-      return;
+  } catch (error: unknown) {
+    if (error instanceof Error) {
+      const errno = (error as NodeJS.ErrnoException).code;
+      if (errno === 'ESRCH') {
+        return;
+      }
     }
     throw error;
   }
@@ -151,7 +178,8 @@ async function loadTreeKill(): Promise<TreeKillFn | null> {
   try {
     const treeKillModule = await import(moduleName);
     return (treeKillModule.default ?? treeKillModule) as TreeKillFn;
-  } catch {
+  } catch (error: unknown) {
+    logger.debug('SYSTEM', 'tree-kill module not available, using fallback', {}, error instanceof Error ? error : undefined);
     return null;
   }
 }