fix: default logging to stdout with configurable target

docs/cli.mdx

@@ -24,12 +24,13 @@ sandbox-agent server [OPTIONS]
 | `-A, --cors-allow-header <HEADER>` | all | CORS allowed header (repeatable) |
 | `-C, --cors-allow-credentials` | - | Enable CORS credentials |
 | `--no-telemetry` | - | Disable anonymous telemetry |
+| `--log-to-file` | - | Redirect server logs to a daily log file |
 
 ```bash
 sandbox-agent server --token "$TOKEN" --port 3000
 ```
 
-Server logs are redirected to a daily log file under the sandbox-agent data directory (for example, `~/.local/share/sandbox-agent/logs`). Override with `SANDBOX_AGENT_LOG_DIR`, or set `SANDBOX_AGENT_LOG_STDOUT=1` to keep logs on stdout/stderr.
+Server logs print to stdout/stderr by default. Use `--log-to-file` or `SANDBOX_AGENT_LOG_TO_FILE=1` to redirect logs to a daily log file under the sandbox-agent data directory (for example, `~/.local/share/sandbox-agent/logs`). Override the directory with `SANDBOX_AGENT_LOG_DIR`, or set `SANDBOX_AGENT_LOG_STDOUT=1` to force stdout/stderr.
 
 HTTP request logging is enabled by default. Control it with:
 - `SANDBOX_AGENT_LOG_HTTP=0` to disable request logs

research/opencode-tmux-test.md

@@ -9,7 +9,8 @@ This plan captures OpenCode TUI output and sends input via tmux so we can valida
 
 ## Environment
 - `SANDBOX_AGENT_LOG_DIR=/path` to set server log dir
-- `SANDBOX_AGENT_LOG_STDOUT=1` to keep logs on stdout/stderr
+- `SANDBOX_AGENT_LOG_TO_FILE=1` to redirect logs to files
+- `SANDBOX_AGENT_LOG_STDOUT=1` to force logs on stdout/stderr
 - `SANDBOX_AGENT_LOG_HTTP=0` to disable request logs
 - `SANDBOX_AGENT_LOG_HTTP_HEADERS=1` to include request headers (Authorization redacted)
 - `RUST_LOG=...` for trace filtering
@@ -42,7 +43,7 @@ This plan captures OpenCode TUI output and sends input via tmux so we can valida
    ```bash
    tmux capture-pane -pt opencode:0.0 -S -200 > /tmp/opencode-screen.txt
    ```
-6. Inspect server logs for requests:
+6. Inspect server logs for requests (when log-to-file is enabled):
    ```bash
    tail -n 200 ~/.local/share/sandbox-agent/logs/log-$(date +%m-%d-%y)
    ```

server/packages/sandbox-agent/src/main.rs

@@ -92,6 +92,9 @@ struct ServerArgs {
 
     #[arg(long = "no-telemetry")]
     no_telemetry: bool,
+
+    #[arg(long = "log-to-file")]
+    log_to_file: bool,
 }
 
 #[derive(Args, Debug)]
@@ -388,8 +391,8 @@ fn main() {
 }
 
 fn init_logging(cli: &Cli) -> Result<(), CliError> {
-    if matches!(cli.command, Command::Server(_)) {
-        maybe_redirect_server_logs();
+    if let Command::Server(server) = &cli.command {
+        maybe_redirect_server_logs(server);
     }
 
     let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info"));
@@ -472,8 +475,20 @@ fn default_server_log_dir() -> PathBuf {
         .unwrap_or_else(|| PathBuf::from(".").join(".sandbox-agent").join("logs"))
 }
 
-fn maybe_redirect_server_logs() {
-    if std::env::var("SANDBOX_AGENT_LOG_STDOUT").is_ok() {
+fn maybe_redirect_server_logs(server: &ServerArgs) {
+    let force_stdout = match std::env::var("SANDBOX_AGENT_LOG_STDOUT") {
+        Ok(value) if value == "0" || value.eq_ignore_ascii_case("false") => false,
+        Ok(_) => true,
+        Err(_) => false,
+    };
+    let log_to_file_env = match std::env::var("SANDBOX_AGENT_LOG_TO_FILE") {
+        Ok(value) if value == "0" || value.eq_ignore_ascii_case("false") => false,
+        Ok(_) => true,
+        Err(_) => false,
+    };
+    let log_to_file = server.log_to_file || log_to_file_env;
+
+    if force_stdout || !log_to_file {
         return;
     }