fix: replace host source arg by identity, fix unused variables

- Replace host source file in args by matching against CDB file entry instead
  of removing last positional arg. Fixes "clang++ -c main.cpp -o main.o" case
  where the old logic would strip -o's argument and leave main.cpp in argv.
- Remove unused main_uri bindings in 3 tests (Ruff RUF059)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 16bit-ykiko

src/server/master_server.cpp

@@ -756,20 +756,17 @@ bool MasterServer::fill_compile_args(llvm::StringRef path,
     directory = host_ctx.directory.str();
     arguments.clear();
 
-    // Copy host arguments, replacing the source file path (last non-flag arg)
-    // with the header file path, so the compiler processes the header in context.
-    auto num_args = host_ctx.arguments.size();
-    std::size_t copy_count = num_args;
-    if(copy_count > 0) {
-        llvm::StringRef last(host_ctx.arguments[copy_count - 1]);
-        if(!last.starts_with("-"))
-            copy_count -= 1;
-    }
-    for(std::size_t i = 0; i < copy_count; ++i) {
-        arguments.emplace_back(host_ctx.arguments[i]);
-    }
-    // Append the header file path as the source file.
-    arguments.emplace_back(path);
+    // Copy host arguments, replacing the host source file path with the header
+    // file path.  We identify the host source by matching against the CDB file
+    // entry rather than guessing based on positional order, so that entries like
+    // "clang++ -c main.cpp -o main.o" are handled correctly.
+    for(auto& arg: host_ctx.arguments) {
+        if(llvm::StringRef(arg) == host_path) {
+            arguments.emplace_back(path);
+        } else {
+            arguments.emplace_back(arg);
+        }
+    }
 
     // Inject the preamble so the compiler sees all context code that normally
     // precedes this header in the host translation unit.

tests/integration/test_header_context.py

@@ -32,7 +32,7 @@ def _get(obj, key, default=None):
 @pytest.mark.workspace("header_context")
 async def test_query_context_returns_host_sources(client, workspace):
     """clice/queryContext on a header should return source files that include it."""
-    main_uri, _ = await client.open_and_wait(workspace / "main.cpp")
+    await client.open_and_wait(workspace / "main.cpp")
 
     utils_h = workspace / "utils.h"
     utils_uri, _ = client.open(utils_h)
@@ -71,7 +71,7 @@ async def test_query_context_source_file_returns_cdb_entries(client, workspace):
 @pytest.mark.workspace("header_context")
 async def test_current_context_default_null(client, workspace):
     """clice/currentContext should return null context by default."""
-    main_uri, _ = await client.open_and_wait(workspace / "main.cpp")
+    await client.open_and_wait(workspace / "main.cpp")
 
     utils_h = workspace / "utils.h"
     utils_uri, _ = client.open(utils_h)
@@ -190,7 +190,7 @@ async def test_full_context_flow(client, workspace):
 async def test_deep_nested_header_context(client, workspace):
     """queryContext on a deeply nested header (main.cpp -> utils.h -> inner.h)
     should still find main.cpp as the host source."""
-    main_uri, _ = await client.open_and_wait(workspace / "main.cpp")
+    await client.open_and_wait(workspace / "main.cpp")
 
     inner_h = workspace / "inner.h"
     inner_uri, _ = client.open(inner_h)