Prevent Julia LS setup from clobbering Serena's stdio MCP pipe (#1580)

* Prevent Julia LS probe from clobbering Serena's stdio MCP pipe

When Serena runs over the stdio MCP transport, stdin/stdout *are* the JSON-RPC channel.
The Julia language-server setup spawns probe/install subprocesses with `capture_output=True`,
which redirects the child's stdout/stderr but not its stdin, so the Julia child inherits
Serena's stdin (the MCP pipe) and clobbers it. The stdio server then exits within
milliseconds of `initialize`, and the client reports "tools fetch failed".

- Pass `stdin=subprocess.DEVNULL` to both `subprocess.run` calls in `julia_server.py`
  (`_setup_runtime_dependency` probe and `_install_language_server` install).
- Add a comment explaining the stdio-transport hazard.

Fixes #1577

* Add changelog entry for the Julia stdio MCP fix

Document the fix under the Unreleased "Language Servers" section.

CHANGELOG.md

@@ -32,6 +32,10 @@ Status of the `main` branch. Changes prior to the next official version change w
     results in svelte-only mode (`languages: [svelte]`). They are now routed to the companion TS server,
     so symbols defined in plain `.ts`/`.js` files are again discoverable via `find_symbol`/
     `get_symbols_overview`, and `find_referencing_symbols` no longer fails to locate `.ts`/`.js` symbols. #1552
+  - `JuliaLanguageServer`: Fix the stdio MCP server exiting right after `initialize` ("tools fetch failed")
+    when `julia` is enabled. The runtime probe/install subprocesses now run with `stdin=subprocess.DEVNULL`,
+    so they can no longer inherit and clobber Serena's stdin, which is the JSON-RPC pipe under the stdio
+    transport. #1577
   - Improve quoting of arguments in shell executions
 
 * JetBrains:

src/solidlsp/language_servers/julia_server.py

@@ -78,10 +78,14 @@ class JuliaLanguageServer(SolidLanguageServer):
                 f"Checked locations: {common_locations}"
             )
 
-        # Check if LanguageServer.jl is installed
+        # Check if LanguageServer.jl is installed.
+        # stdin=DEVNULL: when Serena runs over the stdio MCP transport, the JSON-RPC
+        # channel *is* the process stdin/stdout. Without this, the Julia child inherits
+        # Serena's stdin (the MCP pipe) and clobbers it, killing the server right after
+        # initialize ("tools fetch failed"). See https://github.com/oraios/serena/issues/1577
         check_cmd = [julia_path, "-e", "using LanguageServer"]
         try:
-            result = subprocess.run(check_cmd, check=False, capture_output=True, text=True, timeout=10)
+            result = subprocess.run(check_cmd, check=False, capture_output=True, text=True, timeout=10, stdin=subprocess.DEVNULL)
             if result.returncode != 0:
                 # LanguageServer.jl not found, install it
                 JuliaLanguageServer._install_language_server(julia_path)
@@ -99,7 +103,9 @@ class JuliaLanguageServer(SolidLanguageServer):
         install_cmd = [julia_path, "-e", 'using Pkg; Pkg.add("LanguageServer")']
 
         try:
-            result = subprocess.run(install_cmd, check=False, capture_output=True, text=True, timeout=300)  # 5 minutes for installation
+            result = subprocess.run(
+                install_cmd, check=False, capture_output=True, text=True, timeout=300, stdin=subprocess.DEVNULL
+            )  # 5 minutes for installation
 
             if result.returncode == 0:
                 log.info("LanguageServer.jl installed successfully!")