perf(cli): parallelize detect script for faster first-turn

libs/cli/deepagents_cli/local_context.py

@@ -53,7 +53,8 @@ def execute(self, command: str) -> ExecuteResponse: ...
 # with `command -v` before use.
 #
 # The script is built from section functions so each piece can be tested
-# independently.
+# independently. Independent sections run as parallel background subshells;
+# see build_detect_script() for the orchestration logic.
 # ---------------------------------------------------------------------------
 
 
@@ -278,7 +279,7 @@ def _section_makefile() -> str:
     """First 20 lines of Makefile (falls back to git root in monorepos).
 
     Returns:
-        Bash snippet (requires `ROOT` from `_section_project`).
+        Bash snippet (requires `ROOT` from `_section_project` and `CWD` from header).
     """
     return r"""# --- Makefile ---
 MK=""
@@ -300,21 +301,41 @@ def _section_makefile() -> str:
 def build_detect_script() -> str:
     """Concatenate all section functions into the full detection script.
 
+    Independent sections run as parallel background jobs writing to temp
+    files, then results are concatenated in the original display order.
+    The header (CWD / IN_GIT) and project section (sets ROOT) run first
+    because later sections depend on their variables.
+
     Returns:
         Complete bash heredoc ready for `backend.execute()`.
     """
-    sections = [
-        _section_header(),
-        _section_project(),
-        _section_package_managers(),
-        _section_runtimes(),
-        _section_git(),
-        _section_test_command(),
-        _section_files(),
-        _section_tree(),
-        _section_makefile(),
+    # Header + project run synchronously (set CWD, IN_GIT, ROOT for others)
+    serial_prefix = f"{_section_header()}\n{_section_project()}"
+
+    # These sections are independent — run them in parallel.
+    # Subshells inherit parent variables (IN_GIT, ROOT, CWD) via fork.
+    # Individual exit codes are not tracked because sections legitimately
+    # exit non-zero when they have nothing to report (e.g. no runtimes).
+    parallel_sections = [
+        ("02_pkgmgr", _section_package_managers()),
+        ("03_runtimes", _section_runtimes()),
+        ("04_git", _section_git()),
+        ("05_testcmd", _section_test_command()),
+        ("06_files", _section_files()),
+        ("07_tree", _section_tree()),
+        ("08_makefile", _section_makefile()),
     ]
-    body = "\n".join(sections)
+
+    # Build parallel wrapper: each section runs in a subshell writing to a
+    # temp file. Stderr is captured per-section to prevent noise leakage.
+    parallel_setup = "_DCT=$(mktemp -d) || exit 1\ntrap 'rm -rf \"$_DCT\"' EXIT"
+    parallel_block = "\n".join(
+        f'(\n{body}\n) > "$_DCT/{name}" 2>"$_DCT/{name}.err" &'
+        for name, body in parallel_sections
+    )
+    cat_line = "cat " + " ".join(f'"$_DCT/{name}"' for name, _ in parallel_sections)
+
+    body = f"{serial_prefix}\n{parallel_setup}\n{parallel_block}\nwait\n{cat_line}"
     return f"bash <<'__DETECT_CONTEXT_EOF__'\n{body}\n__DETECT_CONTEXT_EOF__\n"