[WSLC] Generate session names when containerId is omitted

docs/backends/wslc/wsl-container-getting-started.md

@@ -352,6 +352,15 @@ WSLC-specific settings go under `wslc` in the JSON config:
 | `imageTarPath` | string | — | Path to a local tar file to import as the image |
 | `portMappings` | array | `[]` | Host→container TCP forwards; each entry takes `windowsPort` and `containerPort` |
 
+### `containerId` names the WSL session
+
+A create-and-run request names its WSL session after the top-level
+`containerId`. The field is optional: omit it and the run gets a generated
+name of the form `mxc-wslc-<uuid>`, fresh on every run.
+
+Supply your own only when you need a name you can recognise — two runs sharing
+one `containerId` are not isolated from each other by the id alone.
+
 ### Port mappings
 
 ```json

docs/schema.md

@@ -181,7 +181,8 @@ that can be executed independently.
 ```json
 {
     "version": "1.0.0",                    // Exact schema version. Minimum supported: "0.9.0-alpha"; current stable: "1.0.0".
-    "containerId": "my-container",         // Externally assigned container ID
+    "containerId": "my-container",         // Optional externally assigned container ID.
+                                           //  Omit it to use backend-defined internal naming.
     "containment": "processcontainer",     // Backend (see table below)
 
     "lifecycle": {

src/mxc-sdk/src/backends/wslc/common/wsl_container_runner.rs

@@ -492,6 +492,21 @@ fn reject_unsupported_lifecycle(request: &ExecutionRequest) -> Result<(), Script
     Ok(())
 }
 
+const GENERATED_SESSION_NAME_PREFIX: &str = "mxc-wslc-";
+
+/// Name the WSLc session a run gets, minting one when `containerId` is absent:
+/// WSLc refuses an empty name with `WSLC_E_INVALID_SESSION_NAME` (0x80040608).
+fn resolve_session_name(container_id: &str) -> String {
+    if container_id.is_empty() {
+        format!(
+            "{GENERATED_SESSION_NAME_PREFIX}{}",
+            uuid::Uuid::new_v4().simple()
+        )
+    } else {
+        container_id.to_string()
+    }
+}
+
 impl WSLContainerRunner {
     /// Configure session settings and create the session.
     /// Returns the session guard (RAII).
@@ -506,7 +521,8 @@ impl WSLContainerRunner {
         request: &ExecutionRequest,
         logger: &mut Logger,
     ) -> Result<WslcSessionGuard, ScriptResponse> {
-        let session_name: Vec<u16> = to_wide(&request.container_id);
+        let session_name_str = resolve_session_name(&request.container_id);
+        let session_name: Vec<u16> = to_wide(&session_name_str);
         let storage_path_str = self.config.storage_path.clone().unwrap_or_else(|| {
             std::env::temp_dir()
                 .join("mxc-wslc-sessions")
@@ -574,7 +590,7 @@ impl WSLContainerRunner {
             let msg = err_msg.to_string_lossy();
             return Err(sdk_error("WslcCreateSession failed", hr, &msg));
         }
-        let _ = writeln!(logger, "[WSLC] Session created");
+        let _ = writeln!(logger, "[WSLC] Session created: {session_name_str}");
 
         Ok(WslcSessionGuard::from_raw(
             session,
@@ -2270,4 +2286,29 @@ mod tests {
 
         assert!(message.contains("ensure WSL2 and the WSLC SDK are installed"));
     }
+
+    #[test]
+    fn session_name_is_the_container_id_when_the_request_names_one() {
+        assert_eq!(resolve_session_name("pitest"), "pitest");
+        assert_eq!(resolve_session_name("wslc-hello-world"), "wslc-hello-world");
+    }
+
+    #[test]
+    fn absent_container_id_mints_a_session_name() {
+        let name = resolve_session_name("");
+
+        assert!(
+            name.starts_with(GENERATED_SESSION_NAME_PREFIX),
+            "expected a minted name, got: {name}"
+        );
+        assert!(
+            name.len() > GENERATED_SESSION_NAME_PREFIX.len(),
+            "an empty name is what WSLc refuses with WSLC_E_INVALID_SESSION_NAME, got: {name}"
+        );
+    }
+
+    #[test]
+    fn minted_session_names_do_not_repeat() {
+        assert_ne!(resolve_session_name(""), resolve_session_name(""));
+    }
 }

src/tools/wxc/src/main.rs

@@ -283,7 +283,7 @@ fn log_request(request: &ExecutionRequest, logger: &mut Logger) {
         logger,
         "Container name: {}",
         if request.container_id.is_empty() {
-            "CLI"
+            "(assigned by the backend)"
         } else {
             &request.container_id
         }

tests/configs/wslc_no_container_id.json

@@ -0,0 +1,14 @@
+{
+  "$schema": "../../schemas/stable/mxc-config.schema.1.0.0.json",
+  "version": "1.0.0",
+  "containment": "wslc",
+  "process": {
+    "commandLine": "sh -c 'echo NO_CONTAINER_ID_OK'"
+  },
+  "network": {
+    "egress": { "default": "deny" }
+  },
+  "wslc": {
+    "image": "alpine:latest"
+  }
+}

tests/scripts/run_wslc_all_tests.ps1

@@ -248,6 +248,11 @@ $null = $results.Add((Run-WslcTest "wslc_exit_code.json" -ExpectedExit 42 -Outpu
 $null = $results.Add((Run-WslcTest "wslc_stderr.json" -OutputContains "stdout message"))
 $null = $results.Add((Run-WslcTest "wslc_large_output.json"))
 
+# `containerId` is optional, and WSLc refuses the empty session name that an
+# omitted one used to produce (WSLC_E_INVALID_SESSION_NAME, 0x80040608). Every
+# other config here sets the field, so this is the only guard on that path.
+$null = $results.Add((Run-WslcTest "wslc_no_container_id.json" -OutputContains "NO_CONTAINER_ID_OK"))
+
 Write-Host "`n--- Environment Tests ---" -ForegroundColor Cyan
 # PYTHON_VERSION is baked into the image by ENV. Unlike PATH and TERM, no shell
 # fabricates it when it starts without one, so its absence is real evidence that