fix(email): support legacy AI gateway models

backend/tests/emailEntitySuggestions.test.ts

@@ -2,8 +2,10 @@ import assert from "node:assert/strict"
 import test from "node:test"
 import {
     buildSuggestionMail,
+    buildEntitySuggestionRequest,
     dismissEntitySuggestion,
     selectCandidates,
+    shouldRetryWithLegacyAiModel,
     validateSuggestions,
     type EntityCandidate,
 } from "../src/modules/email/email.entity-suggestions"
@@ -69,3 +71,22 @@ test("dismisses only the selected entity suggestion", () => {
     )
     assert.deepEqual(dismissEntitySuggestion(null, "customers", 1), [])
 })
+
+test("uses Luna by default and omits reasoning effort for the legacy fallback", () => {
+    const request = buildEntitySuggestionRequest(buildSuggestionMail({ subject: "Test" }), [customer])
+    assert.equal(request.model, "gpt-5.6-luna")
+    assert.equal(request.reasoning_effort, "none")
+
+    const fallback = buildEntitySuggestionRequest(buildSuggestionMail({ subject: "Test" }), [customer], "gpt-4o-mini")
+    assert.equal(fallback.model, "gpt-4o-mini")
+    assert.equal("reasoning_effort" in fallback, false)
+})
+
+test("retries model compatibility errors without retrying auth, rate-limit, or configuration errors", () => {
+    for (const status of [400, 404, 422, 500, 502]) {
+        assert.equal(shouldRetryWithLegacyAiModel({ status }), true)
+    }
+    for (const status of [401, 403, 429, 503]) {
+        assert.equal(shouldRetryWithLegacyAiModel({ status }), false)
+    }
+})