fix: align sync fallback chain, fix model-fallback test determinism

- Hoist resolveFallbackChainForCallOmoAgent before sync/background branch
  so sync executor also receives the fallback chain
- Add fallbackChain parameter to sync-executor with setSessionFallbackChain
- Mock connected-providers-cache in event.model-fallback tests for
  deterministic behavior (no dependency on local cache files)
- Update test expectations to account for no-op fallback skip when
  normalized current model matches first fallback entry
- Add cache spy isolation for subagent-resolver fallback_models tests

src/tools/delegate-task/subagent-resolver.test.ts

@@ -108,6 +108,11 @@ describe("resolveSubagentExecution", () => {
 
   test("uses agent override fallback_models for subagent runtime fallback chain", async () => {
     //#given
+    const cacheSpy = spyOn(connectedProvidersCache, "readProviderModelsCache").mockReturnValue({
+      models: { quotio: ["claude-haiku-4-5"] },
+      connected: ["quotio"],
+      updatedAt: "2026-03-03T00:00:00.000Z",
+    })
     const args = createBaseArgs({ subagent_type: "explore" })
     const executorCtx = createExecutorContext(
       async () => ([
@@ -131,10 +136,16 @@ describe("resolveSubagentExecution", () => {
       { providers: ["quotio"], model: "gpt-5.2", variant: undefined },
       { providers: ["quotio"], model: "glm-5", variant: "max" },
     ])
+    cacheSpy.mockRestore()
   })
 
   test("uses category fallback_models when agent override points at category", async () => {
     //#given
+    const cacheSpy = spyOn(connectedProvidersCache, "readProviderModelsCache").mockReturnValue({
+      models: { anthropic: ["claude-haiku-4-5"] },
+      connected: ["anthropic"],
+      updatedAt: "2026-03-03T00:00:00.000Z",
+    })
     const args = createBaseArgs({ subagent_type: "explore" })
     const executorCtx = createExecutorContext(
       async () => ([
@@ -162,5 +173,6 @@ describe("resolveSubagentExecution", () => {
     expect(result.fallbackChain).toEqual([
       { providers: ["anthropic"], model: "claude-haiku-4-5", variant: undefined },
     ])
+    cacheSpy.mockRestore()
   })
 })