diff --git a/src/shared/ripgrep-cli.test.ts b/src/shared/ripgrep-cli.test.ts
new file mode 100644
index 000000000..d6fae4b7c
--- /dev/null
+++ b/src/shared/ripgrep-cli.test.ts
@@ -0,0 +1,56 @@
+import { afterEach, beforeEach, describe, expect, it } from "bun:test"
+import { mkdirSync, rmSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { tmpdir } from "node:os"
+
+describe("resolveGrepCli OpenCode cache fallback (#3805)", () => {
+  let tempCache: string
+  let tempData: string
+  let originalCache: string | undefined
+  let originalData: string | undefined
+
+  beforeEach(() => {
+    const stamp = `omo-ripgrep-cli-${process.pid}-${Date.now()}`
+    tempCache = join(tmpdir(), `${stamp}-cache`)
+    tempData = join(tmpdir(), `${stamp}-data`)
+    mkdirSync(tempCache, { recursive: true })
+    mkdirSync(tempData, { recursive: true })
+    originalCache = process.env.XDG_CACHE_HOME
+    originalData = process.env.XDG_DATA_HOME
+    process.env.XDG_CACHE_HOME = tempCache
+    process.env.XDG_DATA_HOME = tempData
+  })
+
+  afterEach(() => {
+    if (originalCache === undefined) delete process.env.XDG_CACHE_HOME
+    else process.env.XDG_CACHE_HOME = originalCache
+    if (originalData === undefined) delete process.env.XDG_DATA_HOME
+    else process.env.XDG_DATA_HOME = originalData
+    try {
+      rmSync(tempCache, { recursive: true, force: true })
+      rmSync(tempData, { recursive: true, force: true })
+    } catch {
+      // best-effort cleanup
+    }
+  })
+
+  it("prefers ~/.cache/opencode/bin/rg over ~/.local/share/opencode/bin/rg", async () => {
+    const rgName = process.platform === "win32" ? "rg.exe" : "rg"
+    const cacheBinDir = join(tempCache, "opencode", "bin")
+    const dataBinDir = join(tempData, "opencode", "bin")
+    mkdirSync(cacheBinDir, { recursive: true })
+    mkdirSync(dataBinDir, { recursive: true })
+    const cacheRg = join(cacheBinDir, rgName)
+    const dataRg = join(dataBinDir, rgName)
+    writeFileSync(cacheRg, "")
+    writeFileSync(dataRg, "")
+
+    // Reset the module cache so the singleton cachedCli is fresh.
+    delete require.cache[require.resolve("./ripgrep-cli")]
+    const { resolveGrepCli } = await import("./ripgrep-cli")
+
+    const resolved = resolveGrepCli()
+    expect(resolved.backend).toBe("rg")
+    expect(resolved.path).toBe(cacheRg)
+  })
+})
diff --git a/src/shared/ripgrep-cli.ts b/src/shared/ripgrep-cli.ts
index 3ee9b8a22..5a21c7dab 100644
--- a/src/shared/ripgrep-cli.ts
+++ b/src/shared/ripgrep-cli.ts
@@ -2,7 +2,7 @@ import { spawnSync } from "node:child_process"
 import { existsSync } from "node:fs"
 import { dirname, join } from "node:path"
 import { downloadAndInstallRipgrep, getInstalledRipgrepPath } from "../tools/grep/downloader"
-import { getDataDir } from "./data-path"
+import { getDataDir, getOpenCodeCacheDir } from "./data-path"
 import { log } from "./logger"
 import { PUBLISHED_PACKAGE_NAME } from "./plugin-identity"
 
@@ -48,6 +48,10 @@ function getOpenCodeBundledRg(): string | null {
   const rgName = isWindows ? "rg.exe" : "rg"
 
   const candidates = [
+    // #3805: Upstream OpenCode's Global.Path.bin is cache-backed (~/.cache/opencode/bin),
+    // and its auto-downloaded ripgrep + LSP binaries live there. Probe it first so OMO
+    // reuses tools OpenCode already installed instead of triggering a duplicate download.
+    join(getOpenCodeCacheDir(), "bin", rgName),
     join(getDataDir(), "opencode", "bin", rgName),
     join(execDir, rgName),
     join(execDir, "bin", rgName),