chore(core) Update shell instructions (#6679)

## Summary
Consolidates `shell` and `shell_command` tool instructions.
## Testing 
- [x] Updated tests, tested locally

codex-rs/core/src/tools/spec.rs

@@ -294,9 +294,26 @@ fn create_shell_tool() -> ToolSpec {
         },
     );
 
+    let description  = if cfg!(windows) {
+        r#"Runs a Powershell command (Windows) and returns its output. Arguments to `shell` will be passed to CreateProcessW(). Most commands should be prefixed with ["powershell.exe", "-Command"].
+        
+Examples of valid command strings:
+
+- ls -a (show hidden): ["powershell.exe", "-Command", "Get-ChildItem -Force"]
+- recursive find by name: ["powershell.exe", "-Command", "Get-ChildItem -Recurse -Filter *.py"]
+- recursive grep: ["powershell.exe", "-Command", "Get-ChildItem -Path C:\\myrepo -Recurse | Select-String -Pattern 'TODO' -CaseSensitive"]
+- ps aux | grep python: ["powershell.exe", "-Command", "Get-Process | Where-Object { $_.ProcessName -like '*python*' }"]
+- setting an env var: ["powershell.exe", "-Command", "$env:FOO='bar'; echo $env:FOO"]
+- running an inline Python script: ["powershell.exe", "-Command", "@'\\nprint('Hello, world!')\\n'@ | python -"]"#
+    } else {
+        r#"Runs a shell command and returns its output.
+- The arguments to `shell` will be passed to execvp(). Most terminal commands should be prefixed with ["bash", "-lc"].
+- Always set the `workdir` param when using the shell function. Do not use `cd` unless absolutely necessary."#
+    }.to_string();
+
     ToolSpec::Function(ResponsesApiTool {
         name: "shell".to_string(),
-        description: "Runs a shell command and returns its output.".to_string(),
+        description,
         strict: false,
         parameters: JsonSchema::Object {
             properties,
@@ -341,9 +358,25 @@ fn create_shell_command_tool() -> ToolSpec {
         },
     );
 
+    let description = if cfg!(windows) {
+        r#"Runs a Powershell command (Windows) and returns its output.
+        
+Examples of valid command strings:
+
+- ls -a (show hidden): "Get-ChildItem -Force"
+- recursive find by name: "Get-ChildItem -Recurse -Filter *.py"
+- recursive grep: "Get-ChildItem -Path C:\\myrepo -Recurse | Select-String -Pattern 'TODO' -CaseSensitive"
+- ps aux | grep python: "Get-Process | Where-Object { $_.ProcessName -like '*python*' }"
+- setting an env var: "$env:FOO='bar'; echo $env:FOO"
+- running an inline Python script: "@'\\nprint('Hello, world!')\\n'@ | python -"#
+    } else {
+        r#"Runs a shell command and returns its output.
+- Always set the `workdir` param when using the shell_command function. Do not use `cd` unless absolutely necessary."#
+    }.to_string();
+
     ToolSpec::Function(ResponsesApiTool {
         name: "shell_command".to_string(),
-        description: "Runs a shell command string and returns its output.".to_string(),
+        description,
         strict: false,
         parameters: JsonSchema::Object {
             properties,
@@ -1873,8 +1906,23 @@ mod tests {
         };
         assert_eq!(name, "shell");
 
-        let expected = "Runs a shell command and returns its output.";
-        assert_eq!(description, expected);
+        let expected = if cfg!(windows) {
+            r#"Runs a Powershell command (Windows) and returns its output. Arguments to `shell` will be passed to CreateProcessW(). Most commands should be prefixed with ["powershell.exe", "-Command"].
+        
+Examples of valid command strings:
+
+- ls -a (show hidden): ["powershell.exe", "-Command", "Get-ChildItem -Force"]
+- recursive find by name: ["powershell.exe", "-Command", "Get-ChildItem -Recurse -Filter *.py"]
+- recursive grep: ["powershell.exe", "-Command", "Get-ChildItem -Path C:\\myrepo -Recurse | Select-String -Pattern 'TODO' -CaseSensitive"]
+- ps aux | grep python: ["powershell.exe", "-Command", "Get-Process | Where-Object { $_.ProcessName -like '*python*' }"]
+- setting an env var: ["powershell.exe", "-Command", "$env:FOO='bar'; echo $env:FOO"]
+- running an inline Python script: ["powershell.exe", "-Command", "@'\\nprint('Hello, world!')\\n'@ | python -"]"#
+        } else {
+            r#"Runs a shell command and returns its output.
+- The arguments to `shell` will be passed to execvp(). Most terminal commands should be prefixed with ["bash", "-lc"].
+- Always set the `workdir` param when using the shell function. Do not use `cd` unless absolutely necessary."#
+        }.to_string();
+        assert_eq!(description, &expected);
     }
 
     #[test]
@@ -1888,8 +1936,22 @@ mod tests {
         };
         assert_eq!(name, "shell_command");
 
-        let expected = "Runs a shell command string and returns its output.";
-        assert_eq!(description, expected);
+        let expected = if cfg!(windows) {
+            r#"Runs a Powershell command (Windows) and returns its output.
+        
+Examples of valid command strings:
+
+- ls -a (show hidden): "Get-ChildItem -Force"
+- recursive find by name: "Get-ChildItem -Recurse -Filter *.py"
+- recursive grep: "Get-ChildItem -Path C:\\myrepo -Recurse | Select-String -Pattern 'TODO' -CaseSensitive"
+- ps aux | grep python: "Get-Process | Where-Object { $_.ProcessName -like '*python*' }"
+- setting an env var: "$env:FOO='bar'; echo $env:FOO"
+- running an inline Python script: "@'\\nprint('Hello, world!')\\n'@ | python -"#.to_string()
+        } else {
+            r#"Runs a shell command and returns its output.
+- Always set the `workdir` param when using the shell_command function. Do not use `cd` unless absolutely necessary."#.to_string()
+        };
+        assert_eq!(description, &expected);
     }
 
     #[test]