Strip nil from or-expression fallbacks in conditional branch values

[apiology]

At strong level, a method whose declared @return is ::Boolean is flagged Declared return type ::Boolean does not match inferred type ::Boolean, nil when an or-expression with a nullable left operand is the value of a conditional branch ��� even though nil can't escape the ||:

class Container
  # @param m [Module, nil]
  # @param expected [Module]
  # @return [Boolean]
  def check(m, expected)
    if m.nil?
      fallback
    else
      m <= expected || fallback  # Module#<= returns bool?
    end
  end

  # @return [Boolean]
  def fallback
    true
  end
end

shape	inferred
m <= expected || fallback as method tail	::Boolean ���
same, after return fallback if m.nil? guard	::Boolean ���
same, as the else-branch value of if/else	::Boolean, nil ���

Root cause: DeepInference.reduce_to_value_nodes flattens an :or node into both operand nodes, typing each independently and unioning ��� bypassing Chain::Or#resolve, which strips nil from the union unless every operand is nullable. Method-tail or-expressions go through NodeChainer ��� Chain::Or and get that treatment; conditional branch values go through reduce_to_value_nodes and don't.

The fix drops the :or special case so the node stays whole and routes through Chain::Or like any other or-expression. Two existing node-level specs pinned the flattening as a contract (return 1 || "2" ��� two literal nodes); updated to expect the intact :or node ��� the operand union is preserved by Chain::Or.

Test plan:

• New failing-first specs: node_methods_spec (or-node stays whole) and strong_spec (no false positive on the repro shape)
• Full suite: 1,626 examples, 0 failures, 60 pending

���� This PR was written by Claude (Anthropic's AI assistant) on behalf of @apiology.

���� Generated with Claude Code

https://claude.ai/code/session_01H1FEjW6nMpZrWPmeWX9miT