Sprint 281: DAP Hardening (steps 1933–1937)

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>

editor/src/DAPBreakpointHitDispatcher.h

@@ -0,0 +1,47 @@
+#pragma once
+#include "ASTNodeBreakpointMapper.h"
+#include "DebugAdapterRouter.h"
+#include <string>
+#include <vector>
+
+namespace whetstone {
+
+struct HitResult {
+    std::string language;
+    std::string astNodeId;
+    int         line       = 0;
+    bool        dispatched = false;
+};
+
+class DAPBreakpointHitDispatcher {
+public:
+    // Find the first active breakpoint at source:line, set router to its language.
+    HitResult dispatch(const std::string& source, int line,
+                       const ASTNodeBreakpointMapper& mapper,
+                       DebugAdapterRouter& router) const {
+        for (const auto& bp : mapper.allBreakpoints()) {
+            if (bp.active && bp.source == source && bp.line == line) {
+                router.setActiveLanguage(bp.language);
+                return {bp.language, bp.astNodeId, bp.line, true};
+            }
+        }
+        return {"", "", line, false};
+    }
+
+    // Return a HitResult for every active breakpoint at source:line.
+    // Router ends at the language of the last match.
+    std::vector<HitResult> dispatchAll(const std::string& source, int line,
+                                       const ASTNodeBreakpointMapper& mapper,
+                                       DebugAdapterRouter& router) const {
+        std::vector<HitResult> results;
+        for (const auto& bp : mapper.allBreakpoints()) {
+            if (bp.active && bp.source == source && bp.line == line) {
+                router.setActiveLanguage(bp.language);
+                results.push_back({bp.language, bp.astNodeId, bp.line, true});
+            }
+        }
+        return results;
+    }
+};
+
+} // namespace whetstone