diff --git a/packages/compass-agent/src/cli.test.ts b/packages/compass-agent/src/cli.test.ts
index 1f3aaf54..98a6bd9c 100644
--- a/packages/compass-agent/src/cli.test.ts
+++ b/packages/compass-agent/src/cli.test.ts
@@ -37,6 +37,7 @@ import {
 	AGENT_SOCKET_PATH,
 	authSeedPath,
 	createSeedApiKeyResolver,
+	deriveLitellmMcpUrl,
 	envFilePath,
 	type MainDeps,
 	main,
@@ -181,6 +182,56 @@ describe("resolveRole", () => {
 	});
 });
 
+// The LiteLLM MCP URL is DERIVED from LITELLM_BASE_URL (RIG-2674), matching the
+// wave's SOPS loader (secrets-env.nix): strip a trailing slash, strip a trailing
+// /v1, append /mcp/. The trailing slash is load-bearing (LiteLLM 307-redirects
+// /mcp and MCP clients don't re-POST across the redirect).
+describe("deriveLitellmMcpUrl", () => {
+	test("derives /mcp/ from a /v1 base URL", () => {
+		expect(
+			deriveLitellmMcpUrl({ LITELLM_BASE_URL: "https://llm.example/v1" }),
+		).toBe("https://llm.example/mcp/");
+	});
+
+	test("strips a trailing slash before stripping /v1", () => {
+		// Non-vacuity: without the trailing-slash strip the /v1$ match misses and
+		// the result would be `…/v1//mcp/` — a broken double path.
+		expect(
+			deriveLitellmMcpUrl({ LITELLM_BASE_URL: "https://llm.example/v1/" }),
+		).toBe("https://llm.example/mcp/");
+	});
+
+	test("appends /mcp/ to a base with no /v1 suffix", () => {
+		expect(
+			deriveLitellmMcpUrl({ LITELLM_BASE_URL: "https://llm.example" }),
+		).toBe("https://llm.example/mcp/");
+	});
+
+	test("keeps the load-bearing trailing slash", () => {
+		// The whole point of the derivation: /mcp (no slash) 307-redirects and the
+		// MCP client drops the POST body. The result MUST end in a slash.
+		const url = deriveLitellmMcpUrl({
+			LITELLM_BASE_URL: "https://llm.example/v1",
+		});
+		expect(url?.endsWith("/mcp/")).toBe(true);
+	});
+
+	test("returns undefined when LITELLM_BASE_URL is unset (no gateway configured)", () => {
+		expect(deriveLitellmMcpUrl({})).toBeUndefined();
+	});
+
+	test("treats an empty or whitespace-only base as unset", () => {
+		expect(deriveLitellmMcpUrl({ LITELLM_BASE_URL: "" })).toBeUndefined();
+		expect(deriveLitellmMcpUrl({ LITELLM_BASE_URL: "   " })).toBeUndefined();
+	});
+
+	test("trims surrounding whitespace so a padded base still derives", () => {
+		expect(
+			deriveLitellmMcpUrl({ LITELLM_BASE_URL: "  https://llm.example/v1  " }),
+		).toBe("https://llm.example/mcp/");
+	});
+});
+
 // The seed path is the frozen T5 placement: a 0600 `$HOME/.compass/auth-seed.json`
 // written by the Runner's materializer.
 describe("authSeedPath", () => {
@@ -1379,6 +1430,8 @@ describe("main sources $HOME/.compass/env into process.env", () => {
 		"COMPASS_MODEL",
 		"OTEL_EXPORTER_OTLP_ENDPOINT",
 		"COMPASS_FUTURE_VAR",
+		"LITELLM_BASE_URL",
+		"LITELLM_MCP_URL",
 	] as const;
 	let savedEnv: Record<string, string | undefined> = {};
 	beforeEach(() => {
@@ -1461,6 +1514,76 @@ describe("main sources $HOME/.compass/env into process.env", () => {
 		);
 		expect(process.env.COMPASS_FUTURE_VAR).toBeUndefined();
 	});
+
+	test("derives LITELLM_MCP_URL from a delivered LITELLM_BASE_URL (RIG-2674)", async () => {
+		const home = process.env.HOME as string;
+		// The keyring delivers only the base URL (+ API key). Without the derive,
+		// LITELLM_MCP_URL stays unset and the fleet mcp.json's ${LITELLM_MCP_URL}
+		// expands empty → the LiteLLM MCP server can't connect. Non-vacuity: with
+		// the derive removed this assertion reds (undefined, not the /mcp/ URL).
+		delete process.env.LITELLM_MCP_URL;
+		writeEnvFile(home, "LITELLM_BASE_URL=https://llm.example/v1\n");
+		await main(
+			{ HOME: home },
+			deps(
+				fakeSession(),
+				fakeCarrier(emptyLog(), { control: emptyControlStream }),
+			),
+		);
+		expect(process.env.LITELLM_MCP_URL as string | undefined).toBe(
+			"https://llm.example/mcp/",
+		);
+	});
+
+	test("LITELLM_MCP_URL is derived BEFORE the MCP manager connects (the load-bearing ordering)", async () => {
+		// The whole point of the fix is that the MCP connector — which reads
+		// ${LITELLM_MCP_URL} from process.env — sees the derived value. Asserting
+		// it only after main() resolves would pass even if a future refactor moved
+		// the derive AFTER the connect. Capture process.env AT the connect instant
+		// via the connectMcp seam (main calls it unconditionally, cli.ts:729, after
+		// loadMountedConfig and before session construction). Non-vacuity: move the
+		// derive block below the connect and this reds (undefined at capture) while
+		// the post-resolve assertion above would still pass.
+		const home = process.env.HOME as string;
+		delete process.env.LITELLM_MCP_URL;
+		writeEnvFile(home, "LITELLM_BASE_URL=https://llm.example/v1\n");
+		let atConnect: string | undefined = "UNSET-SENTINEL";
+		await main(
+			{ HOME: home },
+			{
+				...deps(
+					fakeSession(),
+					fakeCarrier(emptyLog(), { control: emptyControlStream }),
+				),
+				connectMcp: (_cwd, _mcp) => {
+					atConnect = process.env.LITELLM_MCP_URL;
+					return Promise.resolve({
+						tools: [] as never,
+						disconnect: () => Promise.resolve(),
+					});
+				},
+			},
+		);
+		expect(atConnect).toBe("https://llm.example/mcp/");
+	});
+
+	test("an explicitly-delivered LITELLM_MCP_URL wins over the derivation", async () => {
+		const home = process.env.HOME as string;
+		// If a deployer ever delivers the MCP URL directly (env file), the derive
+		// must not clobber it — same file-defines-it posture as the merge loop.
+		writeEnvFile(
+			home,
+			"LITELLM_BASE_URL=https://llm.example/v1\nLITELLM_MCP_URL=https://override.example/mcp/\n",
+		);
+		await main(
+			{ HOME: home },
+			deps(
+				fakeSession(),
+				fakeCarrier(emptyLog(), { control: emptyControlStream }),
+			),
+		);
+		expect(process.env.LITELLM_MCP_URL).toBe("https://override.example/mcp/");
+	});
 });
 
 // A Control stream that closes cleanly with no ops — the shortest complete run.
diff --git a/packages/compass-agent/src/cli.ts b/packages/compass-agent/src/cli.ts
index 08e5a237..e3c3a2f4 100644
--- a/packages/compass-agent/src/cli.ts
+++ b/packages/compass-agent/src/cli.ts
@@ -180,6 +180,33 @@ export function resolveRole(
 	return raw ? raw : undefined;
 }
 
+/**
+ * The LiteLLM MCP endpoint, DERIVED from the delivered `LITELLM_BASE_URL`
+ * (mirroring the wave's SOPS loader `secrets-env.nix`). Compass's keyring
+ * delivers `LITELLM_BASE_URL` + `LITELLM_API_KEY` but NOT the MCP URL — it is a
+ * derived var, not a stored secret — so the fleet `mcp.json`'s
+ * `${LITELLM_MCP_URL}` would otherwise expand empty and the LiteLLM MCP server
+ * would fail to connect. Deriving (rather than seeding a second secret) keeps a
+ * single source of truth and no base/MCP drift.
+ *
+ * The rule matches the loader byte-for-byte: strip one trailing `/`, strip a
+ * trailing `/v1`, append `/mcp/`. The trailing slash is LOAD-BEARING — LiteLLM
+ * 307-redirects `/mcp` and MCP clients do not re-POST across the redirect
+ * (`secrets-env.nix:27-29`). So `https://host/v1` → `https://host/mcp/`.
+ *
+ * Unset (or blank) base is a legitimate configuration: no LiteLLM gateway is
+ * configured, so nothing to derive — returns undefined and `main` leaves
+ * `LITELLM_MCP_URL` untouched. Same unset/trim semantics as `resolveModelSelector`.
+ */
+export function deriveLitellmMcpUrl(
+	env: Record<string, string | undefined>,
+): string | undefined {
+	const raw = env.LITELLM_BASE_URL?.trim();
+	if (!raw) return undefined;
+	const base = raw.replace(/\/$/, "").replace(/\/v1$/, "");
+	return `${base}/mcp/`;
+}
+
 /** One provider's credential in the seed file. Mirrors the SDK's `ApiKeyCredential`. */
 interface SeedEntry {
 	readonly type?: string;
@@ -522,6 +549,18 @@ export async function main(
 		process.env[key] = value;
 	}
 
+	// Derive LITELLM_MCP_URL from the just-sourced LITELLM_BASE_URL (RIG-2674):
+	// Compass's keyring delivers the base URL + API key but not the derived MCP
+	// URL, so the fleet mcp.json's `${LITELLM_MCP_URL}` would expand empty and the
+	// LiteLLM MCP server would fail to connect. Derive it here — after the env
+	// merge, before the MCP connect below — reading from process.env (where the
+	// merge landed the base). An explicitly-delivered LITELLM_MCP_URL wins (same
+	// file-defines-it posture as the merge); we only fill the gap.
+	if (!process.env.LITELLM_MCP_URL) {
+		const mcpUrl = deriveLitellmMcpUrl(process.env);
+		if (mcpUrl) process.env.LITELLM_MCP_URL = mcpUrl;
+	}
+
 	// The identity overlay; undefined when unset or whitespace-only. What omits
 	// the overlay in that case is the `persona ?` spread guard below (an absent
 	// `systemPrompt` key), not any `||`/`??` subtlety — `resolvePersona` has