Sprint 278: LSP Proxy Hardening (steps 1918-1922)

- LSPMessageValidator: JSON-RPC 2.0 shape validation (method, id type, params type)
- LSPCapabilityNegotiator: per-source capability tracking; shouldRoute gates on declared caps
- LSPRequestThrottler: per-URI/method debounce; blocks rapid didChange floods
- LSPErrorRecovery: per-source health tracking; stale-cache fallback when crashed
- Sprint278IntegrationSummary: poly-parse (C++ + Haskell) end-to-end integration

26/26 tests passing (5+5+5+5+6). All new headers well under 600 lines.
LoRA recorded: sprint278-2026-03-01 (9 calls, 6437 tokens).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

editor/tests/step1920_test.cpp

@@ -0,0 +1,80 @@
+// Step 1920: LSPRequestThrottler
+// Debounces per-URI requests to prevent flooding language servers.
+//
+//  t1: no prior record → shouldAllow true
+//  t2: within debounce window → shouldAllow false
+//  t3: after debounce window expires → shouldAllow true
+//  t4: reset clears uri; resetAll clears everything
+//  t5: lastTimestamp returns -1 for missing, correct value after record
+
+#include "LSPRequestThrottler.h"
+#include <iostream>
+
+namespace ws = whetstone;
+
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+void t1(){
+    T(no_prior_record_allows);
+    ws::LSPRequestThrottler t;
+    C(t.shouldAllow("file:///a.go","textDocument/didChange",1000,500), "no record allows");
+    P();
+}
+
+void t2(){
+    T(within_debounce_window_blocks);
+    ws::LSPRequestThrottler t;
+    t.record("file:///a.go","textDocument/didChange",1000);
+    // 200ms later, 500ms debounce → block
+    C(!t.shouldAllow("file:///a.go","textDocument/didChange",1200,500), "within window blocked");
+    // different method: not throttled
+    C( t.shouldAllow("file:///a.go","textDocument/hover",1200,500), "different method allowed");
+    // different uri: not throttled
+    C( t.shouldAllow("file:///b.go","textDocument/didChange",1200,500), "different uri allowed");
+    P();
+}
+
+void t3(){
+    T(after_debounce_window_allows);
+    ws::LSPRequestThrottler t;
+    t.record("file:///a.go","textDocument/didChange",1000);
+    // exactly at boundary: 1000+500=1500 → allow (>=)
+    C( t.shouldAllow("file:///a.go","textDocument/didChange",1500,500), "at boundary allowed");
+    // past boundary
+    C( t.shouldAllow("file:///a.go","textDocument/didChange",1600,500), "past boundary allowed");
+    P();
+}
+
+void t4(){
+    T(reset_and_resetAll);
+    ws::LSPRequestThrottler t;
+    t.record("file:///a.go","textDocument/didChange",1000);
+    t.record("file:///b.go","textDocument/didChange",1000);
+    t.reset("file:///a.go");
+    C( t.shouldAllow("file:///a.go","textDocument/didChange",1100,500), "a.go reset → allowed");
+    C(!t.shouldAllow("file:///b.go","textDocument/didChange",1100,500), "b.go still throttled");
+    t.resetAll();
+    C( t.shouldAllow("file:///b.go","textDocument/didChange",1100,500), "b.go allowed after resetAll");
+    P();
+}
+
+void t5(){
+    T(lastTimestamp);
+    ws::LSPRequestThrottler t;
+    C(t.lastTimestamp("file:///a.go","textDocument/didChange") == -1, "no record returns -1");
+    t.record("file:///a.go","textDocument/didChange",9999);
+    C(t.lastTimestamp("file:///a.go","textDocument/didChange") == 9999, "correct timestamp");
+    C(t.lastTimestamp("file:///a.go","textDocument/hover") == -1, "different method -1");
+    P();
+}
+
+int main(){
+    std::cout << "Step 1920: LSPRequestThrottler\n";
+    t1(); t2(); t3(); t4(); t5();
+    std::cout << "\n" << p << "/" << (p+f) << " passed\n";
+    return f > 0 ? 1 : 0;
+}