fix: avoid Git context overflow in V2 session diffs

lua/opencode/protocols/v2/operations.lua

@@ -367,6 +367,9 @@ end
 ---@return Promise<OpencodeV2FileDiff[]>
 function M.diff_session(connection, session_id, from, to, reverse_path_map)
   return json_request(connection, 'V2 diff_session', 'GET', '/api/session/' .. session_id .. '/diff', {
+    -- The server's INT_MAX default can overflow Git's hunk merging. Keep effectively
+    -- full-file context below INT_MAX / 2 so side-by-side reconstruction stays valid.
+    context = 1000000000,
     from = from,
     to = to,
   }):and_then(function(value)

tests/unit/protocol_v2_operations_spec.lua

@@ -212,11 +212,23 @@ describe('V2 protocol operations', function()
       end)
       :wait()
     assert.equals('/api/session/ses_123/diff', request.path)
-    assert.equals('from=msg_one&to=msg_two', request.query)
+    assert.equals('context=1000000000&from=msg_one&to=msg_two', request.query)
     assert.equals('/host/file.lua', files[1].file)
     assert.equals('@@ -1 +1 @@\n-old\n+new', files[1].patch)
   end)
 
+  it('requests bounded full-file context even without explicit turn boundaries', function()
+    local request
+    transport.request = function(_, value)
+      request = value
+      return Promise.new():resolve({ status = 200, body = '{"data":[]}' })
+    end
+    assert.same({}, operations.diff_session(ready_connection(), 'ses_123'):wait())
+    assert.equals('GET', request.method)
+    assert.equals('/api/session/ses_123/diff', request.path)
+    assert.equals('context=1000000000', request.query)
+  end)
+
   it('uses direct, location/data, and page response contracts from the V2 fixtures', function()
     local bodies = {
       ['/api/location'] = fixture('location.json'),