fix(grep): enable ripgrep auto-download when not found in PATH

The auto-download mechanism for ripgrep existed but was never called.
When 'rg' wasn't in PATH, the grep tool silently fell back to GNU grep,
which wastes ~10% token budget due to noisy results.

Changes:
1. Wired up resolveGrepCliWithAutoInstall() in the CLI resolution path
2. When 'rg' is not found in PATH, auto-downloads ripgrep v14.1.1
3. Caches the downloaded binary in OpenCode data directory
4. Falls back to GNU grep only if auto-download fails (with warning)

Fixes #3003

src/tools/grep/tools.ts

@@ -2,6 +2,7 @@ import { resolve } from "node:path"
 import type { PluginInput } from "@opencode-ai/plugin"
 import { tool, type ToolDefinition } from "@opencode-ai/plugin/tool"
 import { runRg, runRgCount } from "./cli"
+import { resolveGrepCliWithAutoInstall } from "./constants"
 import { formatGrepResult, formatCountResult } from "./result-formatter"
 
 export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition> {
@@ -42,13 +43,14 @@ export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition
         const paths = [searchPath]
         const outputMode = args.output_mode ?? "files_with_matches"
         const headLimit = args.head_limit ?? 0
+        const cli = await resolveGrepCliWithAutoInstall()
 
         if (outputMode === "count") {
           const results = await runRgCount({
             pattern: args.pattern,
             paths,
             globs,
-          })
+          }, cli)
           const limited = headLimit > 0 ? results.slice(0, headLimit) : results
           return formatCountResult(limited)
         }
@@ -60,7 +62,7 @@ export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition
           context: 0,
           outputMode,
           headLimit,
-        })
+        }, cli)
 
         return formatGrepResult(result)
       } catch (e) {