fix(tools): throttle ripgrep CPU usage with thread limits and concurrency control

- Add --threads=4 flag to all rg invocations (grep and glob)
- Add global semaphore limiting concurrent rg processes to 2
- Reduce grep timeout from 300s to 60s (matches tool description)
- Reduce max output from 10MB to 256KB (prevents excessive memory usage)
- Add output_mode parameter (content/files_with_matches/count)
- Add head_limit parameter for incremental result fetching

Closes #2008

Ref: #674, #1722

src/tools/grep/tools.ts

@@ -1,16 +1,16 @@
 import type { PluginInput } from "@opencode-ai/plugin"
 import { tool, type ToolDefinition } from "@opencode-ai/plugin/tool"
-import { runRg } from "./cli"
-import { formatGrepResult } from "./result-formatter"
+import { runRg, runRgCount } from "./cli"
+import { formatGrepResult, formatCountResult } from "./result-formatter"
 
 export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition> {
   const grep: ToolDefinition = tool({
     description:
-      "Fast content search tool with safety limits (60s timeout, 10MB output). " +
+      "Fast content search tool with safety limits (60s timeout, 256KB output). " +
       "Searches file contents using regular expressions. " +
       "Supports full regex syntax (eg. \"log.*Error\", \"function\\s+\\w+\", etc.). " +
       "Filter files by pattern with the include parameter (eg. \"*.js\", \"*.{ts,tsx}\"). " +
-      "Returns file paths with matches sorted by modification time.",
+      "Output modes: \"content\" shows matching lines, \"files_with_matches\" shows only file paths (default), \"count\" shows match counts per file.",
     args: {
       pattern: tool.schema.string().describe("The regex pattern to search for in file contents"),
       include: tool.schema
@@ -21,18 +21,42 @@ export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition
         .string()
         .optional()
         .describe("The directory to search in. Defaults to the current working directory."),
+      output_mode: tool.schema
+        .string()
+        .optional()
+        .describe(
+          "Output mode: \"content\" shows matching lines, \"files_with_matches\" shows only file paths (default), \"count\" shows match counts per file."
+        ),
+      head_limit: tool.schema
+        .number()
+        .optional()
+        .describe("Limit output to first N entries. 0 or omitted means no limit."),
     },
     execute: async (args) => {
       try {
         const globs = args.include ? [args.include] : undefined
         const searchPath = args.path ?? ctx.directory
         const paths = [searchPath]
+        const outputMode = (args.output_mode as "content" | "files_with_matches" | "count") ?? "files_with_matches"
+        const headLimit = args.head_limit ?? 0
+
+        if (outputMode === "count") {
+          const results = await runRgCount({
+            pattern: args.pattern,
+            paths,
+            globs,
+          })
+          const limited = headLimit > 0 ? results.slice(0, headLimit) : results
+          return formatCountResult(limited)
+        }
 
         const result = await runRg({
           pattern: args.pattern,
           paths,
           globs,
           context: 0,
+          outputMode,
+          headLimit,
         })
 
         return formatGrepResult(result)