refactor(windows): clarify unix command usage and add tests

Clarified that built-in tools are safe to use, only discouraged in shell execution. Added unit tests for Windows guidance injection.

src/agents/system-prompt.test.ts

@@ -369,4 +369,32 @@ describe("buildAgentSystemPrompt", () => {
     expect(prompt).toContain("## Reactions");
     expect(prompt).toContain("Reactions are enabled for Telegram in MINIMAL mode.");
   });
+
+  it("includes Windows Shell Guidance when running on Windows", () => {
+    const prompt = buildAgentSystemPrompt({
+      workspaceDir: "/tmp/clawd",
+      runtimeInfo: {
+        os: "Windows_NT",
+        host: "host",
+        agentId: "agent",
+      },
+    });
+
+    expect(prompt).toContain("## Windows Shell Guidance");
+    expect(prompt).toContain("You are running on Windows (PowerShell).");
+  });
+
+  it("omits Windows Shell Guidance when running on non-Windows", () => {
+    const prompt = buildAgentSystemPrompt({
+      workspaceDir: "/tmp/clawd",
+      runtimeInfo: {
+        os: "Darwin",
+        host: "host",
+        agentId: "agent",
+      },
+    });
+
+    expect(prompt).not.toContain("## Windows Shell Guidance");
+    expect(prompt).not.toContain("You are running on Windows (PowerShell).");
+  });
 });

src/agents/system-prompt.ts

@@ -404,7 +404,7 @@ export function buildAgentSystemPrompt(params: {
         "## Windows Shell Guidance",
         "You are running on Windows (PowerShell).",
         "- Use PowerShell syntax (e.g. `$env:VAR` instead of `%VAR%` or `$VAR`).",
-        "- Do NOT use Unix commands like `grep`, `sed`, `awk`, `head`, `tail` unless you are sure they are installed.",
+        "- Do NOT use Unix commands like `grep`, `sed`, `awk`, `head`, `tail` in exec/shell (PowerShell) commands unless you are sure they are installed. Pi's built-in tools named `grep`, `find`, and `ls` are safe to use.",
         "- Use `findstr` or `Select-String` instead of `grep`.",
         "- Use `Get-ChildItem` (dir/ls) with `-Recurse` instead of `find`.",
         "",