DAPRequestValidator, DAPCapabilityNegotiator, DAPEventBroadcaster, DAPBreakpointHitDispatcher — 26/26 tests pass. Integration step 1937: Python+Rust DAP session round-trip verified. Also adds allBreakpoints() to ASTNodeBreakpointMapper. Metrics: 8 whetstone calls, 8853 tokens. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>