Fix ArithmeticError in ServeShapePlug when parse_body halts before telemetry span

.changeset/fix-telemetry-arithmetic-error.md

@@ -0,0 +1,5 @@
+---
+"@core/sync-service": patch
+---
+
+Fixed ArithmeticError in `ServeShapePlug.end_telemetry_span/2` when `parse_body` halts before the telemetry span is started. Moved `parse_body` plug after `start_telemetry_span` in the pipeline.

.github/workflows/claude-code-review.yml

@@ -114,4 +114,5 @@ jobs:
 
             Start by reading `.claude/commands/pr-review.md`, then follow its phases to conduct the review.
 
+          allowed_bots: 'claude[bot]'
           claude_args: '--allowedTools "Bash(gh issue view:*),Bash(gh search:*),Bash(gh issue list:*),Bash(gh pr comment:*),Bash(gh pr diff:*),Bash(gh pr view:*),Bash(gh pr list:*),Bash(gh api:*),Bash(cat:*),Read,Glob,Grep"'

packages/sync-service/lib/electric/plug/serve_shape_plug.ex

@@ -12,12 +12,12 @@ defmodule Electric.Plug.ServeShapePlug do
 
   require Logger
 
+  plug :put_resp_content_type, "application/json"
   plug :fetch_query_params
-  plug :parse_body
 
   # start_telemetry_span needs to always be the first plug after fetching query params.
   plug :start_telemetry_span
-  plug :put_resp_content_type, "application/json"
+  plug :parse_body
 
   plug :validate_request
   # Admission control is applied here, but note:

packages/sync-service/test/electric/plug/serve_shape_plug_test.exs

@@ -1028,6 +1028,66 @@ defmodule Electric.Plug.ServeShapePlugTest do
     end
   end
 
+  describe "parse_body error handling" do
+    setup :with_lsn_tracker
+
+    setup ctx do
+      {:via, _, {registry_name, registry_key}} =
+        Electric.Shapes.Supervisor.name(ctx.stack_id)
+
+      {:ok, _} = Registry.register(registry_name, registry_key, nil)
+      set_status_to_active(ctx)
+
+      patch_storage(for_shape: fn @test_shape_handle, _opts -> @test_opts end)
+
+      :ok
+    end
+
+    test "returns 400 for invalid JSON body without crashing", ctx do
+      conn =
+        Plug.Test.conn(:post, "/?offset=-1", "not valid json")
+        |> put_req_header("content-type", "application/json")
+        |> call_serve_shape_plug(ctx)
+
+      assert conn.status == 400
+      assert %{"error" => "Invalid JSON in request body"} = Jason.decode!(conn.resp_body)
+    end
+
+    test "returns 400 for non-object JSON body without crashing", ctx do
+      conn =
+        Plug.Test.conn(:post, "/?offset=-1", Jason.encode!(["an", "array"]))
+        |> put_req_header("content-type", "application/json")
+        |> call_serve_shape_plug(ctx)
+
+      assert conn.status == 400
+      assert %{"error" => "Request body must be a JSON object"} = Jason.decode!(conn.resp_body)
+    end
+
+    test "returns 413 for oversized body without crashing", ctx do
+      Repatch.patch(Plug.Conn, :read_body, fn conn, _opts -> {:more, "partial", conn} end)
+
+      conn =
+        Plug.Test.conn(:post, "/?offset=-1", "body")
+        |> put_req_header("content-type", "application/json")
+        |> call_serve_shape_plug(ctx)
+
+      assert conn.status == 413
+      assert %{"error" => "Request body too large"} = Jason.decode!(conn.resp_body)
+    end
+
+    test "returns 400 for body read failure without crashing", ctx do
+      Repatch.patch(Plug.Conn, :read_body, fn _conn, _opts -> {:error, :timeout} end)
+
+      conn =
+        Plug.Test.conn(:post, "/?offset=-1", "body")
+        |> put_req_header("content-type", "application/json")
+        |> call_serve_shape_plug(ctx)
+
+      assert conn.status == 400
+      assert %{"error" => "Failed to read request body"} = Jason.decode!(conn.resp_body)
+    end
+  end
+
   describe "stack not ready" do
     test "returns 503", ctx do
       conn =