diff --git a/build.py b/build.py
index 9b82104b..989525e4 100644
--- a/build.py
+++ b/build.py
@@ -133,7 +133,7 @@ class Module:
         name="v2-market-stream",
         language="Ruby",
         dir=ROOT / "v2" / "services",
-        build_cmd=["ruby", "-c", "market_stream.rb"],
+        build_cmd=["ruby", "market_stream_test_runner.rb"],
         clean_cmd=["echo", "Ruby has no build artifacts to clean"],
         build_dir=None,
     ),
diff --git a/diagnostic/build-00000000.json b/diagnostic/build-00000000.json
deleted file mode 100644
index 33e2ca62..00000000
--- a/diagnostic/build-00000000.json
+++ /dev/null
@@ -1,23 +0,0 @@
-{
-  "generated_at": "2026-06-16T15:23:47.496569+00:00",
-  "commit": "00000000",
-  "diagnostic_logd": "diagnostic/build-00000000.logd",
-  "diagnostic_logd_error": null,
-  "chunked": false,
-  "chunk_size_bytes": null,
-  "password": "4c7df15ab09fbb066197",
-  "decrypt_command": "encryptly unpack diagnostic/build-00000000.logd <outdir> --password 4c7df15ab09fbb066197",
-  "total_modules": 1,
-  "passed": 0,
-  "failed": 1,
-  "modules": [
-    {
-      "name": "frailbox",
-      "status": "FAIL",
-      "elapsed_seconds": 0,
-      "artifact": null,
-      "output": "Command not found: [Errno 2] No such file or directory: 'make'"
-    }
-  ],
-  "pr_note": "Include this JSON diagnostic report and diagnostic/build-00000000.logd in your PR. Maintainers may ask you to remove these diagnostic artifacts before merging."
-}
diff --git a/diagnostic/build-00000000.logd b/diagnostic/build-00000000.logd
deleted file mode 100644
index b5a046a2..00000000
--- a/diagnostic/build-00000000.logd
+++ /dev/null
@@ -1 +0,0 @@
-stub diagnostic logd placeholder
diff --git a/diagnostic/build-6c985129-part001.logd b/diagnostic/build-6c985129-part001.logd
new file mode 100644
index 00000000..91fcaefe
Binary files /dev/null and b/diagnostic/build-6c985129-part001.logd differ
diff --git a/diagnostic/build-6c985129-part002.logd b/diagnostic/build-6c985129-part002.logd
new file mode 100644
index 00000000..76d0d3e9
Binary files /dev/null and b/diagnostic/build-6c985129-part002.logd differ
diff --git a/diagnostic/build-6c985129.json b/diagnostic/build-6c985129.json
new file mode 100644
index 00000000..9f552f43
--- /dev/null
+++ b/diagnostic/build-6c985129.json
@@ -0,0 +1,26 @@
+{
+  "generated_at": "2026-06-20T15:53:17.144005+00:00",
+  "commit": "6c985129",
+  "diagnostic_logd": [
+    "diagnostic\\build-6c985129-part001.logd",
+    "diagnostic\\build-6c985129-part002.logd"
+  ],
+  "diagnostic_logd_error": null,
+  "chunked": true,
+  "chunk_size_bytes": 41943040,
+  "password": "551a715c6ecfe495fc90",
+  "decrypt_command": "encryptly unpack diagnostic\\build-6c985129.logd <outdir> --password 551a715c6ecfe495fc90",
+  "total_modules": 1,
+  "passed": 0,
+  "failed": 1,
+  "modules": [
+    {
+      "name": "v2-market-stream",
+      "status": "FAIL",
+      "elapsed_seconds": 0,
+      "artifact": null,
+      "output": "Command not found: [WinError 2] \u7cfb\u7edf\u627e\u4e0d\u5230\u6307\u5b9a\u7684\u6587\u4ef6\u3002"
+    }
+  ],
+  "pr_note": "Include the encrypted diagnostic logd artifact(s): diagnostic\\build-6c985129-part001.logd, diagnostic\\build-6c985129-part002.logd. The encrypted .logd is the required diagnostic content for PR review; this JSON file is metadata. Maintainers may ask you to remove these diagnostic artifacts before merging."
+}
diff --git a/v2/services/market_stream.rb b/v2/services/market_stream.rb
index 6eeb63a4..1210a046 100644
--- a/v2/services/market_stream.rb
+++ b/v2/services/market_stream.rb
@@ -55,6 +55,8 @@
 require 'sinatra/base'
 require 'logger'
 
+require_relative 'market_stream_backoff'
+
 # ===─ Fucking Constants =================================================================================─
 
 V2_VERSION = '2.0.0'
@@ -216,10 +218,11 @@ def schedule_reconnect
     # v2 reconnection: exponential backoff with max. We learned. We grew.
     return if Constants::WS_MAX_RECONNECTS && @reconnect_attempt >= Constants::WS_MAX_RECONNECTS
 
-    delay = [
-      Constants::WS_RECONNECT_BASE * (2 ** @reconnect_attempt),
-      Constants::WS_RECONNECT_MAX
-    ].min
+    delay = MarketStreamBackoff.delay_for(
+      @reconnect_attempt,
+      base: Constants::WS_RECONNECT_BASE,
+      max: Constants::WS_RECONNECT_MAX
+    )
 
     @reconnect_attempt += 1
 
diff --git a/v2/services/market_stream_backoff.rb b/v2/services/market_stream_backoff.rb
new file mode 100644
index 00000000..57b7995a
--- /dev/null
+++ b/v2/services/market_stream_backoff.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module MarketStreamBackoff
+  module_function
+
+  def delay_for(attempt, base: 1, max: 120, jitter: 0.0, rng: Random::DEFAULT)
+    raise ArgumentError, 'attempt must be non-negative' if attempt.negative?
+    raise ArgumentError, 'base must be positive' unless base.positive?
+    raise ArgumentError, 'max must be positive' unless max.positive?
+    raise ArgumentError, 'jitter must be between 0.0 and 1.0' unless jitter.between?(0.0, 1.0)
+
+    capped_delay = [base.to_f * (2**attempt), max.to_f].min
+    return normalized(capped_delay) if jitter.zero?
+
+    spread = capped_delay * jitter
+    jittered_delay = capped_delay + (((rng.rand * 2.0) - 1.0) * spread)
+    normalized([[jittered_delay, 0.0].max, max.to_f].min)
+  end
+
+  def normalized(value)
+    value == value.to_i ? value.to_i : value
+  end
+end
diff --git a/v2/services/market_stream_backoff_test.rb b/v2/services/market_stream_backoff_test.rb
new file mode 100644
index 00000000..d4fe699f
--- /dev/null
+++ b/v2/services/market_stream_backoff_test.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require 'minitest/autorun'
+require_relative 'market_stream_backoff'
+
+class MarketStreamBackoffTest < Minitest::Test
+  class FixedRandom
+    def initialize(*values)
+      @values = values
+    end
+
+    def rand
+      @values.shift || 0.5
+    end
+  end
+
+  def test_initial_delay_uses_base_delay
+    assert_equal 1, MarketStreamBackoff.delay_for(0, base: 1, max: 120)
+  end
+
+  def test_delay_grows_exponentially
+    assert_equal 2, MarketStreamBackoff.delay_for(1, base: 1, max: 120)
+    assert_equal 64, MarketStreamBackoff.delay_for(6, base: 1, max: 120)
+  end
+
+  def test_delay_is_capped_at_maximum
+    assert_equal 120, MarketStreamBackoff.delay_for(7, base: 1, max: 120)
+    assert_equal 120, MarketStreamBackoff.delay_for(20, base: 1, max: 120)
+  end
+
+  def test_jitter_respects_lower_and_upper_bounds_before_cap
+    assert_in_delta 8.0, MarketStreamBackoff.delay_for(0, base: 10, max: 100, jitter: 0.2, rng: FixedRandom.new(0.0)), 0.0001
+    assert_in_delta 12.0, MarketStreamBackoff.delay_for(0, base: 10, max: 100, jitter: 0.2, rng: FixedRandom.new(1.0)), 0.0001
+  end
+
+  def test_jitter_never_exceeds_maximum_cap
+    assert_equal 50, MarketStreamBackoff.delay_for(4, base: 10, max: 50, jitter: 0.5, rng: FixedRandom.new(1.0))
+  end
+
+  def test_invalid_parameters_are_rejected
+    assert_raises(ArgumentError) { MarketStreamBackoff.delay_for(-1) }
+    assert_raises(ArgumentError) { MarketStreamBackoff.delay_for(0, base: 0) }
+    assert_raises(ArgumentError) { MarketStreamBackoff.delay_for(0, max: 0) }
+    assert_raises(ArgumentError) { MarketStreamBackoff.delay_for(0, jitter: 1.1) }
+  end
+end
diff --git a/v2/services/market_stream_test_runner.rb b/v2/services/market_stream_test_runner.rb
new file mode 100644
index 00000000..cfd2b80b
--- /dev/null
+++ b/v2/services/market_stream_test_runner.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require 'rbconfig'
+
+service_path = File.expand_path('market_stream.rb', __dir__)
+unless system(RbConfig.ruby, '-c', service_path)
+  warn 'market_stream.rb syntax check failed'
+  exit 1
+end
+
+require_relative 'market_stream_backoff_test'