Remove the legacy --single-process mode

coderai now always boots as the front proxy + supervised engine subprocess(es);
the one-process "UI/API and model work in the same process" mode is gone. This
unblocks removing the engine's now-dead UI/stats/data handlers (the engine only
ever runs as --engine-only behind the front).

Removed: the --single-process CLI flag (cli.py), config.server.single_process
(config.py + save), the proc-title branch and the run-mode branch (main.py), and
the arg from the engine spawn filter (engine_supervisor.py). Existing config.json
files with a stale single_process key are tolerated (_dc ignores unknown keys).

Verified: argparse rejects --single-process; --engine-only still parses.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011DDv7BchtZQWsnPG6Jm49m

codai/cli.py

@@ -303,13 +303,6 @@ configuration directory (--config DIR, default: OS-specific CoderAI directory).
              "run (use after changing a model's quantization/precision config).",
     )
     # ─── Frontend/engine split ───────────────────────────────────────────────
-    parser.add_argument(
-        "--single-process",
-        action="store_true",
-        help="Run the legacy single-process server (UI/API and all model work in "
-             "one process). Default boots a front proxy + supervised engine "
-             "subprocess(es) so the web UI stays responsive during model work.",
-    )
     parser.add_argument(
         "--engine-only",
         action="store_true",

codai/config.py

@@ -41,12 +41,10 @@ class ServerConfig:
     # use the default above.
     max_parallel_requests_overrides: dict = field(default_factory=dict)
     # ─── Frontend/engine split ───────────────────────────────────────────────
-    # By default coderai boots a thin, always-responsive *front* reverse proxy on
-    # the public host/port and supervises one or more *engine* subprocesses (which
-    # do all GPU/model work) on internal localhost ports. This keeps the web UI
-    # responsive while a model loads or generates. Set single_process=True (or pass
-    # --single-process) to keep the legacy one-process behavior.
-    single_process: bool = False
+    # coderai boots a thin, always-responsive *front* reverse proxy on the public
+    # host/port and supervises one or more *engine* subprocesses (which do all
+    # GPU/model work) on internal localhost ports. This keeps the web UI responsive
+    # while a model loads or generates.
     internal_port_base: int = 8780      # first engine binds here; +1 per extra engine
     engines: int = 0                    # 0 = auto (one per detected GPU, min 1)
     engine_gpus: Optional[list] = None  # explicit GPU indices, e.g. [0, 1]; None = auto
@@ -595,7 +593,6 @@ class ConfigManager:
                 "queue_max_size": self.config.server.queue_max_size,
                 "max_parallel_requests": self.config.server.max_parallel_requests,
                 "max_parallel_requests_overrides": self.config.server.max_parallel_requests_overrides,
-                "single_process": self.config.server.single_process,
                 "internal_port_base": self.config.server.internal_port_base,
                 "engines": self.config.server.engines,
                 "engine_gpus": self.config.server.engine_gpus,

codai/frontproxy/engine_supervisor.py

@@ -283,7 +283,7 @@ class EngineSupervisor:
             if skip_next:
                 skip_next = False
                 continue
-            if a in ("--single-process", "--engine-only"):
+            if a == "--engine-only":
                 continue
             if a == "--internal-port":
                 skip_next = True

codai/main.py

@@ -345,8 +345,6 @@ def _set_proc_title():
         _ename = (os.environ.get("CODERAI_ENGINE_NAME")
                   or os.environ.get("CODERAI_ENGINE_BACKEND") or "engine")
         name = f"coderai-{_ename}"
-    elif "--single-process" in _argv:
-        name = "coderai"
     else:
         name = "coderai-front"
     try:
@@ -604,10 +602,8 @@ def main():
     # below runs in it (so its event loop is never blocked by model work).
     #   --engine-only     → this process IS an engine: bind an internal localhost
     #                       port and run the full app below (the front spawns these).
-    #   --single-process  → legacy: one process, full app on the public port.
     _engine_only = getattr(args, "engine_only", False)
-    _single_process = getattr(args, "single_process", False) or config.server.single_process
-    if not _engine_only and not _single_process:
+    if not _engine_only:
         from codai.frontproxy import run_front
         run_front(config, args)
         return
@@ -1342,9 +1338,8 @@ def main():
     # Start the server
     import uvicorn
     # The bind target: an engine binds 127.0.0.1:<internal-port> with plain HTTP
-    # (the front owns the public host + TLS); single-process uses the configured
-    # public host/port/https. config.server keeps the CONFIGURED values either way
-    # so the settings API reports them correctly.
+    # (the front owns the public host + TLS). config.server keeps the CONFIGURED
+    # values so the settings API reports them correctly.
     if getattr(args, 'engine_only', False):
         bind_host = "127.0.0.1"
         bind_port = int(getattr(args, "internal_port", None)