docs(metrics): Clarify batch size rationale with topFilesLength context

Explain that metrics may process only a small number of top files
(topFilesLength * 10 = 50 by default) when tokenCountTree is disabled,
which is why a smaller batch size of 10 is needed. Update security
check comment to match.

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

Author: yamadashy

src/core/metrics/calculateSelectiveFileMetrics.ts

@@ -9,10 +9,11 @@ import type { FileMetrics } from './workers/types.js';
 // Batch size for grouping files into worker tasks to reduce IPC overhead.
 // Each batch is sent as a single message to a worker thread, avoiding
 // per-file round-trip costs (~0.5ms each) that dominate when processing many files.
-// A size of 10 keeps individual worker tasks small so that workers become
-// available sooner, enabling overlap between file metrics and output token
-// counting. While smaller batches increase total IPC overhead, the cost is
-// distributed across available workers and offset by improved utilization.
+// A size of 10 keeps individual worker tasks small so that workers become available sooner,
+// enabling overlap between file metrics and output token counting.
+// When tokenCountTree is disabled, metrics only processes a small number of top files
+// (e.g., topFilesLength * 10 = 50 by default), so a smaller batch size avoids
+// a single batch monopolizing one worker.
 const METRICS_BATCH_SIZE = 10;
 
 export const calculateSelectiveFileMetrics = async (

src/core/security/securityCheck.ts

@@ -23,8 +23,8 @@ export interface SuspiciousFileResult {
 // per-file round-trip costs that dominate when processing many files.
 // Security check always processes all files (~1000 in a typical repo), so a batch size of 50
 // already produces ~20 batches — enough to distribute well across available CPU cores.
-// (Unlike metrics, which may process only top N files and needs a smaller batch size of 10
-// to avoid a single batch monopolizing one worker.)
+// (Unlike metrics, which may process only a small number of top files when tokenCountTree
+// is disabled, and needs a smaller batch size to avoid one batch monopolizing a worker.)
 const BATCH_SIZE = 50;
 
 export const runSecurityCheck = async (