fix(chatcore): restore missing mergeResponseToolNameMap import

Genuine pre-existing bug on upstream release/v3.8.50 (verified byte-
identical to their tip, not introduced by this branch's merge): chatCore.ts
calls mergeResponseToolNameMap() but never imports it from
./chatCore/passthroughToolNames.ts, throwing a ReferenceError on every
request that reaches that line (surfaced by
agentrouter-chatcore-protocols.test.ts's 3 streaming-protocol cases).

Also renumbers this branch's own migrations from 137/138 back to a
contiguous 136/137 — the earlier 135->137 renumber (done to resolve this
branch's collision with upstream's independently-added
135_migrate_model_capability_max_token.sql) skipped 136 entirely, leaving
an unexplained sequence gap that check-migration-numbering.test.ts's real-
migrations-dir check correctly flagged.

open-sse/handlers/chatCore.ts

@@ -223,6 +223,7 @@ import { recordCost } from "@/domain/costRules";
 import { calculateCost } from "@/lib/usage/costCalculator";
 import {
   buildClaudePassthroughToolNameMap,
+  mergeResponseToolNameMap,
   normalizeOpenAIToolFinishReasons,
   restoreNonStreamingToolNames,
 } from "./chatCore/passthroughToolNames.ts";

src/lib/db/agenticConversations.ts

@@ -7,7 +7,7 @@
  *
  * `last_message_count`/`last_messages_hash` on `agentic_conversations` are
  * dead columns kept only for backward on-disk compatibility (superseded by
- * `conversation_turn_nodes`, migration 138) — never read, written as
+ * `conversation_turn_nodes`, migration 137) — never read, written as
  * placeholders.
  */
 
@@ -51,7 +51,7 @@ export function createAgenticConversation(input: {
   const id = input.id || `conv_${uuidv4()}`;
 
   // last_message_count/last_messages_hash are dead columns (superseded by
-  // conversation_turn_nodes, migration 138) — 0/'' placeholders only.
+  // conversation_turn_nodes, migration 137) — 0/'' placeholders only.
   db.prepare(
     `INSERT INTO agentic_conversations
        (id, api_key_id, fingerprint_hash, last_message_count, last_messages_hash, turn_count, first_seen_at, last_seen_at)
@@ -89,7 +89,7 @@ export function updateAgenticConversation(id: string, patch: { turnCount: number
   );
 }
 
-// ── Turn-node tree (migration 138) ───────────────────────────────────────
+// ── Turn-node tree (migration 137) ───────────────────────────────────────
 
 export interface ConversationTurnNode {
   id: string;

src/lib/db/migrations/136_agentic_conversations.sql

@@ -1,4 +1,4 @@
--- 137_agentic_conversations.sql
+-- 136_agentic_conversations.sql
 -- Stable multi-turn conversation tracking for /v1/chat/completions and
 -- /v1/responses. Clients resend the full growing message/input history on
 -- every turn; this table lets us detect "request N's history is request

src/lib/db/migrations/137_conversation_turn_nodes.sql

@@ -1,4 +1,4 @@
--- 138_conversation_turn_nodes.sql
+-- 137_conversation_turn_nodes.sql
 -- Per-turn hash-chain nodes backing a conversation's linear transcript
 -- (open-sse/services/conversationTracker.ts). Each row is one distinct
 -- turn instance, chained to its predecessor the same way a git commit
@@ -9,7 +9,7 @@
 -- duplicates a turn mid-history to keep provider-side prompt caches warm)
 -- becomes its OWN independent conversation instead (2026-08-06 — every
 -- OmniRoute conversation is a single straight line, it never forks; see
--- resolveConversationId's doc comment). See agentic_conversations (137) for
+-- resolveConversationId's doc comment). See agentic_conversations (136) for
 -- the conversation-root record; its last_message_count/last_messages_hash
 -- columns are superseded by this table and no longer written to.
 --