refactor(http): route every reject-before-read through one arming helper

Replaces the inline `handler.close_connection = True` at each reject-before-read
site with api.helpers.arm_connection_close(), the shared mechanism the review
asked for. Behaviour is unchanged at every real handler; the helper adds the
same stub tolerance the read side just got, so a handler that refuses the
attribute can never turn a 4xx into a 500.

Sites: _check_csrf (origin + token), the sidecar provenance 403 (body-reading
calls only), the rate-limited CSP report, /api/health/restart, the deprecated
process-complete-ack 410, and all four upload handlers' pre-read
length/boundary rejections.

api/routes.py

@@ -2974,6 +2974,7 @@ from api.helpers import (
     require,
     bad,
     safe_resolve,
+    arm_connection_close,
     j,
     t,
     read_body,
@@ -5873,7 +5874,7 @@ def _check_csrf(handler) -> bool:
     if not _check_same_origin_browser_request(handler):
         # CSRF checks run before read_body().  Close rather than reusing an
         # HTTP/1.1 connection whose unread body would corrupt the next request.
-        handler.close_connection = True
+        arm_connection_close(handler)
         return False
     if not _is_browser_unsafe_request(handler):
         return True  # non-browser clients (curl, MCP, agent) have no Origin/Referer
@@ -5886,7 +5887,7 @@ def _check_csrf(handler) -> bool:
     submitted = handler.headers.get(CSRF_HEADER_NAME) or handler.headers.get("X-CSRF-Token")
     if verify_csrf_token(cookie_val or "", submitted or ""):
         return True
-    handler.close_connection = True
+    arm_connection_close(handler)
     return _set_csrf_failure_reason(handler, "token_mismatch")
 
 
@@ -6071,7 +6072,7 @@ def _handle_extension_sidecar_proxy(
         # unread body would corrupt the next request (same class as _check_csrf).
         # GET (read_request_body=False) has nothing unread — keep-alive survives.
         if read_request_body:
-            handler.close_connection = True
+            arm_connection_close(handler)
         return j(handler, {"error": _csrf_rejection_error(handler)}, status=403)
     try:
         request_body = _read_body_bytes(handler) if read_request_body else None
@@ -6516,7 +6517,7 @@ def _handle_csp_report(handler) -> bool:
         )
         # Rate-limit rejection runs before the body is read; close-and-advertise
         # so the unread report can't corrupt the next pooled request.
-        handler.close_connection = True
+        arm_connection_close(handler)
         return _send_no_content(handler)
 
     payload = _read_csp_report_payload(handler)
@@ -12910,7 +12911,7 @@ def _handle_health_restart(handler) -> bool:
     """Restart the Hermes messaging gateway service."""
     # This endpoint never consumes its request body on any outcome; close so a
     # supplied body can't corrupt the next pooled request.
-    handler.close_connection = True
+    arm_connection_close(handler)
     outcome = restart_active_profile_gateway()
 
     if outcome.get("status") == "completed":
@@ -15236,7 +15237,7 @@ def handle_post(handler, parsed) -> bool:
             # The 410 runs before the stale tab's JSON body is read;
             # close-and-advertise so those unread bytes can't corrupt the next
             # pooled request.
-            handler.close_connection = True
+            arm_connection_close(handler)
             j(
                 handler,
                 {

api/upload.py

@@ -8,7 +8,7 @@ import tempfile
 from pathlib import Path
 
 from api.config import MAX_UPLOAD_BYTES, STATE_DIR
-from api.helpers import j
+from api.helpers import arm_connection_close, j
 from api.models import get_session
 from api.profiles import _profiles_match, get_active_profile_name as _get_active_profile_name
 from api.workspace import (
@@ -47,7 +47,7 @@ _MAX_EXTRACTED_BYTES = 10 * MAX_UPLOAD_BYTES
 
 def _reject_before_read(handler, message, status):
     """Reject without reading the body; close so unread bytes can't poison HTTP/1.1 reuse."""
-    handler.close_connection = True
+    arm_connection_close(handler)
     return j(handler, {'error': message}, status=status)
 
 
@@ -217,7 +217,7 @@ def handle_upload(handler):
             content_length = int(handler.headers.get('Content-Length', 0) or 0)
         except (TypeError, ValueError):
             # A non-numeric Content-Length is rejected before the body is read.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise ValueError('Invalid Content-Length') from None
         if content_length > MAX_UPLOAD_BYTES:
             return _reject_before_read(handler, f'File too large (max {MAX_UPLOAD_BYTES//1024//1024}MB)', 413)
@@ -226,7 +226,7 @@ def handle_upload(handler):
         except ValueError:
             # parse_multipart validates Content-Length/boundary before reading;
             # a ValueError here means the body was never consumed.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise
         session_id = fields.get('session_id', '')
         if 'file' not in files:
@@ -418,7 +418,7 @@ def handle_upload_extract(handler):
             content_length = int(handler.headers.get('Content-Length', 0) or 0)
         except (TypeError, ValueError):
             # A non-numeric Content-Length is rejected before the body is read.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise ValueError('Invalid Content-Length') from None
         if content_length > MAX_UPLOAD_BYTES:
             return _reject_before_read(handler, f'File too large (max {MAX_UPLOAD_BYTES//1024//1024}MB)', 413)
@@ -427,7 +427,7 @@ def handle_upload_extract(handler):
         except ValueError:
             # parse_multipart validates Content-Length/boundary before reading;
             # a ValueError here means the body was never consumed.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise
         session_id = fields.get('session_id', '')
         if 'file' not in files:
@@ -461,7 +461,7 @@ def handle_transcribe(handler):
             content_length = int(handler.headers.get('Content-Length', 0) or 0)
         except (TypeError, ValueError):
             # A non-numeric Content-Length is rejected before the body is read.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise ValueError('Invalid Content-Length') from None
         if content_length > MAX_UPLOAD_BYTES:
             return _reject_before_read(handler, f'File too large (max {MAX_UPLOAD_BYTES//1024//1024}MB)', 413)
@@ -470,7 +470,7 @@ def handle_transcribe(handler):
         except ValueError:
             # parse_multipart validates Content-Length/boundary before reading;
             # a ValueError here means the body was never consumed.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise
         if 'file' not in files:
             return j(handler, {'error': 'No file field in request'}, status=400)
@@ -656,7 +656,7 @@ def handle_workspace_upload(handler):
             content_length = int(handler.headers.get('Content-Length', 0) or 0)
         except (TypeError, ValueError):
             # A non-numeric Content-Length is rejected before the body is read.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise ValueError('Invalid Content-Length') from None
         if content_length > MAX_UPLOAD_BYTES:
             return _reject_before_read(handler, f'File too large (max {MAX_UPLOAD_BYTES//1024//1024}MB)', 413)
@@ -666,7 +666,7 @@ def handle_workspace_upload(handler):
         except ValueError:
             # parse_multipart validates Content-Length/boundary before reading;
             # a ValueError here means the body was never consumed.
-            handler.close_connection = True
+            arm_connection_close(handler)
             raise
         session_id = fields.get('session_id', '')
         subpath = fields.get('path', '')