test(ai-usage): close branch-coverage gaps in the embeddings/buildAiUsage patch

adapters.ts's new embedding-error handler never exercised its non-Error-thrown
branch, and buildAiUsage's model/costUsd/effort branches are structurally
unreachable through its 3 real call sites (none ever pass costUsd/effort, and
model is always defined) -- add a direct unit test via a new
__selfHostAiInternals export, matching this repo's existing internals-export
convention for testing private helpers.

Author: JSONbored

src/selfhost/ai.ts

@@ -1446,3 +1446,5 @@ export function resolveAiReviewerPlan(
 export function withAdvisoryAiEnv(env: Env, useAdvisory: boolean): Env {
   return useAdvisory && env.AI_ADVISORY ? { ...env, AI: env.AI_ADVISORY } : env;
 }
+
+export const __selfHostAiInternals = { buildAiUsage };

test/unit/review-adapters.test.ts

@@ -221,4 +221,22 @@ describe("reviewInferenceAdapter: delegates to env.AI", () => {
     }>();
     expect(row).toMatchObject({ feature: "embeddings", model: "@cf/baai/bge-m3", status: "error", detail: "embed_provider_unreachable" });
   });
+
+  it("records a failed embedding call with the literal fallback detail when the provider throws a non-Error value", async () => {
+    const ai = {
+      run: vi.fn(async () => {
+        throw "not an Error instance";
+      }),
+    };
+    const env = createTestEnv({ AI: ai as unknown as Ai });
+    const adapter = reviewInferenceAdapter(env, ai as unknown as Ai);
+    await expect(adapter.run("@cf/baai/bge-m3", { text: ["hello"] })).rejects.toBe("not an Error instance");
+    const row = await env.DB.prepare("select feature, model, status, detail from ai_usage_events order by rowid desc limit 1").first<{
+      feature: string;
+      model: string;
+      status: string;
+      detail: string | null;
+    }>();
+    expect(row).toMatchObject({ feature: "embeddings", model: "@cf/baai/bge-m3", status: "error", detail: "embedding_failed" });
+  });
 });

test/unit/selfhost-ai.test.ts

@@ -2,7 +2,7 @@ import { chmodSync, mkdirSync, mkdtempSync, readFileSync, writeFileSync } from "
 import { tmpdir } from "node:os";
 import { delimiter, join } from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
-import { assertNoLegacySharedAiEnv, buildProvider, claudeErrorStatus, codexErrorFromStdout, createAnthropicAi, createChainAi, createClaudeCodeAi, createCodexAi, createOpenAiCompatibleAi, createSelfHostAi, extractCliText, extractCliUsage, isAiProviderHealthy, markAiProviderUnhealthyAtBoot, resetAiProviderCircuitBreakerForTest, resetAiProviderHealthForTest, resolveAiReviewerPlan, resolveClaudeCliTimeoutMs, resolveClaudeFirstOutputTimeoutMs, resolveCodexAuthPath, resolveCodexCliTimeoutMs, resolveCodexEffort, resolveCodexFirstOutputTimeoutMs, resolveEffort, resolveModel, resolveProviderNames, resolveRequiredCliProviders, resolveSubscriptionCliPath, redactSecrets, routeProviders, shouldMarkAiProviderUnhealthyAtBoot, subscriptionCliEnv, withAdvisoryAiEnv } from "../../src/selfhost/ai";
+import { assertNoLegacySharedAiEnv, buildProvider, claudeErrorStatus, codexErrorFromStdout, createAnthropicAi, createChainAi, createClaudeCodeAi, createCodexAi, createOpenAiCompatibleAi, createSelfHostAi, extractCliText, extractCliUsage, isAiProviderHealthy, markAiProviderUnhealthyAtBoot, resetAiProviderCircuitBreakerForTest, resetAiProviderHealthForTest, resolveAiReviewerPlan, resolveClaudeCliTimeoutMs, resolveClaudeFirstOutputTimeoutMs, resolveCodexAuthPath, resolveCodexCliTimeoutMs, resolveCodexEffort, resolveCodexFirstOutputTimeoutMs, resolveEffort, resolveModel, resolveProviderNames, resolveRequiredCliProviders, resolveSubscriptionCliPath, redactSecrets, routeProviders, shouldMarkAiProviderUnhealthyAtBoot, subscriptionCliEnv, withAdvisoryAiEnv, __selfHostAiInternals } from "../../src/selfhost/ai";
 import { labelSelfHostReviewerModel, labelSelfHostReviewerModels } from "../../src/selfhost/ai-config";
 import { renderMetrics, resetMetrics } from "../../src/selfhost/metrics";
 
@@ -215,6 +215,14 @@ describe("createOpenAiCompatibleAi (#979)", () => {
     expect(out).toEqual({ data: [[0.1]], usage: { model: "bge-m3", inputTokens: 7, totalTokens: 7 } });
   });
 
+  it("buildAiUsage omits every undefined field and includes every defined one (direct unit test — costUsd/effort/an-undefined-model are never both exercised through the 3 real call sites)", () => {
+    const { buildAiUsage } = __selfHostAiInternals;
+    expect(buildAiUsage({})).toEqual({});
+    expect(
+      buildAiUsage({ provider: "ollama", model: "m", inputTokens: 1, outputTokens: 2, totalTokens: 3, costUsd: 0.5, effort: "medium" }),
+    ).toEqual({ provider: "ollama", model: "m", inputTokens: 1, outputTokens: 2, totalTokens: 3, costUsd: 0.5, effort: "medium" });
+  });
+
   it("throws on a non-OK embeddings response, including the response body detail (#4996: previously thrown away)", async () => {
     vi.stubGlobal("fetch", vi.fn(async () => new Response("bad request: input exceeds max length", { status: 400 })));
     await expect(createOpenAiCompatibleAi({ baseUrl: "http://x/v1" }).run("m", { text: ["a"] })).rejects.toThrow(