diff --git a/extensions/active-memory/index.test.ts b/extensions/active-memory/index.test.ts
index 7354f7db3f5..8dd18a641c1 100644
--- a/extensions/active-memory/index.test.ts
+++ b/extensions/active-memory/index.test.ts
@@ -1384,6 +1384,22 @@ describe("active-memory plugin", () => {
     expect(api.logger.warn).toHaveBeenCalledWith(
       expect.stringContaining("config.modelFallbackPolicy is deprecated"),
     );
+    // #74587: deprecation warning must spell out the chain-resolution
+    // semantics so operators don't read it as a promise of runtime failover.
+    // The previous wording ("set config.modelFallback if you want a fallback
+    // model") cost real users hours of debug time before they hit the source
+    // and saw `getModelRef` only walks candidates once.
+    const warnCalls = (api.logger.warn as ReturnType<typeof vi.fn>).mock.calls;
+    const deprecationMessage = warnCalls
+      .map(([first]) => (typeof first === "string" ? first : ""))
+      .find((message) => message.includes("config.modelFallbackPolicy is deprecated"));
+    expect(deprecationMessage).toBeDefined();
+    // Positive: the warning describes chain-resolution last-resort behavior.
+    expect(deprecationMessage).toContain("chain-resolution");
+    expect(deprecationMessage).toContain("last-resort");
+    // Negative: the warning explicitly disclaims runtime failover, since
+    // that's the wrong mental model the previous wording invited.
+    expect(deprecationMessage).toMatch(/NOT a runtime failover/i);
   });
 
   it("does not use a built-in fallback model even when default-remote is configured", async () => {
diff --git a/extensions/active-memory/index.ts b/extensions/active-memory/index.ts
index ee89f59cc48..d8b0194fdfa 100644
--- a/extensions/active-memory/index.ts
+++ b/extensions/active-memory/index.ts
@@ -2431,8 +2431,19 @@ export default definePluginEntry({
     let config = normalizePluginConfig(api.pluginConfig);
     const warnDeprecatedModelFallbackPolicy = (pluginConfig: unknown) => {
       if (hasDeprecatedModelFallbackPolicy(pluginConfig)) {
+        // Wording matters here: the previous text ("set config.modelFallback
+        // explicitly if you want a fallback model") read naturally as runtime
+        // failover (model A errors → switch to model B), but `getModelRef`
+        // only consults `modelFallback` as the *last candidate* in the
+        // resolution chain after `config.model`, the current run's model,
+        // and the agent's configured default have all resolved to nothing.
+        // Surface the chain-resolution semantics directly so operators
+        // don't waste debug cycles assuming runtime failover (#74587).
         api.logger.warn?.(
-          "active-memory: config.modelFallbackPolicy is deprecated and no longer changes runtime behavior; set config.modelFallback explicitly if you want a fallback model",
+          "active-memory: config.modelFallbackPolicy is deprecated and no longer changes runtime behavior. " +
+            "config.modelFallback is a chain-resolution last-resort (consulted only when config.model, " +
+            "the current run's model, and the agent's configured default all resolve to nothing) — " +
+            "it is NOT a runtime failover that substitutes a different model when the resolved model errors out.",
         );
       }
     };