fix(claude): drop orphan tool_result after fixToolAdjacency strip (discussion #2410)

Discussion #2410 reports Claude returning 400 for sequences like:
  assistant: tool_use(id=X)
  user: <plain text>           ← breaks adjacency
  user: tool_result(id=X)

The previous round added `fixToolAdjacency` (commit 44d9abac9) which
correctly strips the orphan tool_use from the assistant message. But
that left the now-unmatched tool_result intact, so the upstream
rejected the request with:

  messages.N.content.M: unexpected `tool_use_id` found in `tool_result`
  blocks: X. Each tool_result block must have a corresponding tool_use
  block in the previous message.

Fix: after running `fixToolAdjacency`, re-run `fixToolPairs` to drop
the orphaned tool_result blocks. All three call sites updated:
  - contextManager.purifyHistory (both inside the binary-search loop
    and the final pass)
  - BaseExecutor message-prep (Claude path)
  - claudeCodeCompatible request signer

Also tightens an unrelated dynamic-key access in
readNestedString (claudeCodeCompatible) to satisfy the prototype-
pollution scanner triggered by the post-tool semgrep hook.

open-sse/executors/base.ts

@@ -894,7 +894,10 @@ export class BaseExecutor {
             // Only apply for Claude/Claude-compatible — OpenAI allows results
             // spread across multiple subsequent messages.
             const isClaude = this.provider === "claude" || isClaudeCodeCompatible(this.provider);
-            const adjacent = isClaude ? fixToolAdjacency(fixed) : fixed;
+            // For Claude, fixToolAdjacency may strip tool_use blocks whose
+            // tool_result isn't in the next message; re-run fixToolPairs to
+            // drop any tool_result orphaned by that strip (discussion #2410).
+            const adjacent = isClaude ? fixToolPairs(fixToolAdjacency(fixed)) : fixed;
             tb.messages = stripTrailingAssistantOrphanToolUse(adjacent);
           }
         }

open-sse/services/claudeCodeCompatible.ts

@@ -378,7 +378,11 @@ export async function buildAndSignClaudeCodeRequest(
     if (Array.isArray(b.messages)) {
       const fixed = fixToolPairs(b.messages as Record<string, unknown>[]);
       const adjacent = fixToolAdjacency(fixed);
-      b.messages = stripTrailingAssistantOrphanToolUse(adjacent);
+      // fixToolAdjacency can leave orphan tool_result blocks behind when it
+      // strips a tool_use whose tool_result wasn't in the next message.
+      // Re-pair to drop those orphans (discussion #2410).
+      const cleaned = fixToolPairs(adjacent);
+      b.messages = stripTrailingAssistantOrphanToolUse(cleaned);
     }
   }
 
@@ -1158,7 +1162,9 @@ function readNestedString(
     if (!current || typeof current !== "object" || Array.isArray(current)) {
       return null;
     }
-    current = (current as Record<string, unknown>)[key];
+    if (key === "__proto__" || key === "constructor" || key === "prototype") return null;
+    if (!Object.prototype.hasOwnProperty.call(current, key)) return null;
+    current = Reflect.get(current as object, key);
   }
   return toNonEmptyString(current);
 }

open-sse/services/contextManager.ts

@@ -267,6 +267,9 @@ function purifyHistory(messages: Record<string, unknown>[], targetTokens: number
     let candidate = [...system, ...nonSystem.slice(-keep)];
     candidate = fixToolPairs(candidate);
     candidate = fixToolAdjacency(candidate);
+    // Re-run pair fix: fixToolAdjacency may have stripped tool_use blocks, leaving
+    // orphan tool_results that Claude rejects ("tool_result without preceding tool_use").
+    candidate = fixToolPairs(candidate);
     candidate = stripTrailingAssistantOrphanToolUse(candidate);
     const tokens = estimateTokens(JSON.stringify(candidate));
     if (tokens <= targetTokens) break;
@@ -276,6 +279,9 @@ function purifyHistory(messages: Record<string, unknown>[], targetTokens: number
   let result = [...system, ...nonSystem.slice(-keep)];
   result = fixToolPairs(result);
   result = fixToolAdjacency(result);
+  // Re-run pair fix to drop any tool_result whose matching tool_use was removed by
+  // fixToolAdjacency (discussion #2410 — orphan tool_result -> upstream 400).
+  result = fixToolPairs(result);
   result = stripTrailingAssistantOrphanToolUse(result);
 
   // Add summary of dropped messages