[AI] fix(model): /model <default> writes override when session runs non-default model

xydt-tanshanshan · xydt-tanshanshan · commit 422ff8d7d0c7 · 2026-06-24T17:52:50.000+08:00
Strip isDefault from model selections before applying overrides in the directive-handling paths. When a user explicitly switches to the configured default model via /model, the selection must write an override so the session actually transitions — clearing overrides left the session pinned to the stale runtime model. Related to #96269
diff --git a/src/auto-reply/reply/directive-handling.impl.ts b/src/auto-reply/reply/directive-handling.impl.ts
@@ -455,9 +455,15 @@ export async function handleDirectiveOnly(
       }
     }
     if (modelSelection) {
+      // Strip isDefault so user-requested model switches always write an
+      // explicit override.  When the selected model happens to match the
+      // configured default, retaining isDefault would clear overrides and
+      // leave the session pinned to its current (possibly different)
+      // runtime model (#96269).
+      const { isDefault: _, ...selection } = modelSelection;
       const applied = applyModelOverrideToSessionEntry({
         entry: sessionEntry,
-        selection: modelSelection,
+        selection,
         profileOverride,
         markLiveSwitchPending: true,
       });
diff --git a/src/auto-reply/reply/directive-handling.persist.ts b/src/auto-reply/reply/directive-handling.persist.ts
@@ -267,9 +267,12 @@ export async function persistInlineDirectives(params: {
         provider,
       });
       if (modelResolution.modelSelection) {
+        // Strip isDefault — user-requested model switches always write an
+        // explicit override (#96269).
+        const { isDefault: _, ...selection } = modelResolution.modelSelection;
         const appliedModelOverride = applyModelOverrideToSessionEntry({
           entry: sessionEntry,
-          selection: modelResolution.modelSelection,
+          selection,
           profileOverride: modelResolution.profileOverride,
           markLiveSwitchPending: params.markLiveSwitchPending,
         });
diff --git a/src/sessions/model-overrides.test.ts b/src/sessions/model-overrides.test.ts
@@ -180,6 +180,38 @@ describe("applyModelOverrideToSessionEntry", () => {
     expect((entry.updatedAt ?? 0) > before).toBe(true);
   });
 
+  it("writes default model override when selected without isDefault flag (#96269)", () => {
+    // Regression test for #96269: when a user explicitly selects the
+    // configured default model via /model, the selection must be treated
+    // as an explicit switch (no isDefault flag).  The old behaviour
+    // passed isDefault=true, which cleared overrides and left the
+    // session pinned to the stale runtime model.
+    const before = Date.now() - 5_000;
+    const entry: SessionEntry = {
+      sessionId: "sess-model-cmd-default",
+      updatedAt: before,
+      providerOverride: "tencent-token-plan",
+      modelOverride: "glm-5.1",
+      contextTokens: 128_000,
+    };
+
+    const result = applyModelOverrideToSessionEntry({
+      entry,
+      selection: {
+        provider: "minimax",
+        model: "MiniMax-M3",
+        // No isDefault — mimics directive-handling.impl.ts stripping it
+      },
+    });
+
+    expect(result.updated).toBe(true);
+    // Must write the override so the session actually switches.
+    expect(entry.providerOverride).toBe("minimax");
+    expect(entry.modelOverride).toBe("MiniMax-M3");
+    expect(entry.modelOverrideSource).toBe("user");
+    expect((entry.updatedAt ?? 0) > before).toBe(true);
+  });
+
   it("marks non-default overrides with the provided source", () => {
     const entry: SessionEntry = {
       sessionId: "sess-5a",
