fix(anthropic): preserve base URL path prefix for PDF document requests

src/llm/providers/anthropic.ts

@@ -184,7 +184,12 @@ export async function completeAnthropicDocument({
     throw new Error("Internal error: expected a document attachment for Anthropic.");
   }
   const baseUrl = resolveBaseUrlOverride(anthropicBaseUrlOverride) ?? "https://api.anthropic.com";
-  const url = new URL("/v1/messages", baseUrl);
+  // Join onto the base URL so a path prefix on the override survives. Using
+  // `new URL("/v1/messages", baseUrl)` would treat the absolute path as
+  // root-relative and discard any prefix (e.g. a custom Anthropic-compatible
+  // gateway exposed at `https://host/anthropic` would lose `/anthropic` and
+  // POST to `https://host/v1/messages`). Mirror completeGoogleDocument's join.
+  const url = new URL(`${baseUrl.replace(/\/$/, "")}/v1/messages`);
   const controller = new AbortController();
   const timeout = setTimeout(() => controller.abort(), timeoutMs);
   const payload = {

tests/llm.anthropic-document-url.test.ts

@@ -0,0 +1,108 @@
+import { describe, expect, it, vi } from "vitest";
+
+// completeAnthropicDocument posts a base64 PDF document block to the Anthropic
+// Messages API. The request URL must be built by JOINING `/v1/messages` onto the
+// (optionally overridden) base URL so that a path prefix on a custom
+// Anthropic-compatible gateway is preserved. Using `new URL("/v1/messages", base)`
+// treats the path as root-relative and silently drops any prefix, so a gateway at
+// `https://host/anthropic` would wrongly POST to `https://host/v1/messages` (404/400).
+
+const docInput = {
+  kind: "document" as const,
+  mediaType: "application/pdf" as const,
+  bytes: new Uint8Array([1, 2, 3]),
+  filename: "test.pdf",
+};
+
+function mockOkFetch(captured: string[]) {
+  return vi.fn(async (url: string) => {
+    captured.push(String(url));
+    return {
+      ok: true,
+      status: 200,
+      text: async () =>
+        JSON.stringify({
+          content: [{ type: "text", text: "Summary result" }],
+          usage: { input_tokens: 10, output_tokens: 5 },
+        }),
+    } as unknown as Response;
+  });
+}
+
+describe("completeAnthropicDocument request URL", () => {
+  it("preserves a path prefix on a custom gateway base URL", async () => {
+    const captured: string[] = [];
+    const { completeAnthropicDocument } = await import("../src/llm/providers/anthropic.js");
+
+    await completeAnthropicDocument({
+      modelId: "claude-opus-4-x",
+      apiKey: "test-key",
+      promptText: "Summarize this document",
+      document: docInput,
+      maxOutputTokens: 256,
+      timeoutMs: 30000,
+      fetchImpl: mockOkFetch(captured) as unknown as typeof fetch,
+      anthropicBaseUrlOverride: "https://gateway.example/anthropic",
+    });
+
+    expect(captured.length).toBe(1);
+    expect(captured[0]).toBe("https://gateway.example/anthropic/v1/messages");
+  });
+
+  it("tolerates a trailing slash on the override", async () => {
+    const captured: string[] = [];
+    const { completeAnthropicDocument } = await import("../src/llm/providers/anthropic.js");
+
+    await completeAnthropicDocument({
+      modelId: "claude-opus-4-x",
+      apiKey: "test-key",
+      promptText: "Summarize this document",
+      document: docInput,
+      timeoutMs: 30000,
+      fetchImpl: mockOkFetch(captured) as unknown as typeof fetch,
+      anthropicBaseUrlOverride: "https://gateway.example/anthropic/",
+    });
+
+    expect(captured[0]).toBe("https://gateway.example/anthropic/v1/messages");
+  });
+
+  it("matches the Anthropic SDK/text path for an already-versioned base (no special-casing)", async () => {
+    // The streaming/text path stores ANTHROPIC_BASE_URL verbatim as the model
+    // baseUrl (see resolveAnthropicModel) and lets @anthropic-ai/sdk append
+    // `/v1/messages` via string concat. For a base that already ends in `/v1`
+    // the SDK therefore produces `/v1/v1/messages`. The document path must stay
+    // byte-for-byte consistent with that path rather than inventing a
+    // document-only `/v1`-as-root heuristic (which would make PDF requests
+    // diverge from text/streaming requests for the same configured base).
+    const captured: string[] = [];
+    const { completeAnthropicDocument } = await import("../src/llm/providers/anthropic.js");
+
+    await completeAnthropicDocument({
+      modelId: "claude-opus-4-x",
+      apiKey: "test-key",
+      promptText: "Summarize this document",
+      document: docInput,
+      timeoutMs: 30000,
+      fetchImpl: mockOkFetch(captured) as unknown as typeof fetch,
+      anthropicBaseUrlOverride: "https://anthropic.example/v1",
+    });
+
+    expect(captured[0]).toBe("https://anthropic.example/v1/v1/messages");
+  });
+
+  it("defaults to api.anthropic.com when no override is given", async () => {
+    const captured: string[] = [];
+    const { completeAnthropicDocument } = await import("../src/llm/providers/anthropic.js");
+
+    await completeAnthropicDocument({
+      modelId: "claude-opus-4-x",
+      apiKey: "test-key",
+      promptText: "Summarize this document",
+      document: docInput,
+      timeoutMs: 30000,
+      fetchImpl: mockOkFetch(captured) as unknown as typeof fetch,
+    });
+
+    expect(captured[0]).toBe("https://api.anthropic.com/v1/messages");
+  });
+});