diff --git a/tooling/turbo/source-cache.test.ts b/tooling/turbo/source-cache.test.ts
new file mode 100644
index 000000000..68309efe4
--- /dev/null
+++ b/tooling/turbo/source-cache.test.ts
@@ -0,0 +1,117 @@
+import { execFileSync } from "node:child_process";
+import { mkdir, mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { fileURLToPath } from "node:url";
+import { afterAll, beforeAll, expect, it } from "vitest";
+
+const root = fileURLToPath(new URL("../../", import.meta.url));
+const turbo = join(root, "node_modules", "turbo", "bin", "turbo");
+const tasks = ["build", "check", "typecheck", "test", "test:coverage", "test:ci", "test:agent"];
+type DryTask = { taskId: string; task: string; hash: string; command: string; dependencies: string[] };
+let directory: string;
+let baseline: Map<string, DryTask>;
+
+function dryRun() {
+	const output = execFileSync(process.execPath, [turbo, "run", ...tasks, "--dry=json"], {
+		cwd: directory,
+		encoding: "utf8",
+		maxBuffer: 8 * 1024 * 1024,
+		env: { ...process.env, TURBO_TELEMETRY_DISABLED: "1" },
+	});
+	const result = JSON.parse(output) as { tasks: DryTask[] };
+	return new Map(result.tasks.map((task) => [task.taskId, task]));
+}
+
+beforeAll(async () => {
+	directory = await mkdtemp(join(tmpdir(), "reactive-resume-turbo-cache-"));
+	const packageJson = JSON.parse(await readFile(join(root, "package.json"), "utf8"));
+	await writeFile(
+		join(directory, "package.json"),
+		JSON.stringify({ private: true, packageManager: packageJson.packageManager }),
+	);
+	await writeFile(join(directory, "pnpm-workspace.yaml"), 'packages: ["packages/*"]\n');
+	await writeFile(join(directory, ".gitignore"), "node_modules/\n.turbo/\n");
+	await writeFile(join(directory, "turbo.json"), await readFile(join(root, "turbo.json")));
+
+	// app -> api -> pdf mirrors a source-consumed dependency with no build script.
+	const dependencies: Record<string, string[]> = { app: ["api"], api: ["pdf"], pdf: [], unrelated: [] };
+	let lock = "lockfileVersion: '9.0'\nimporters:\n  .: {}\n";
+	for (const [name, deps] of Object.entries(dependencies)) {
+		const packageDirectory = join(directory, "packages", name);
+		await mkdir(packageDirectory, { recursive: true });
+		await writeFile(join(packageDirectory, "source.ts"), "export const value = 1;\n");
+		await writeFile(
+			join(packageDirectory, "package.json"),
+			JSON.stringify({
+				name,
+				version: "0.0.0",
+				private: true,
+				dependencies: Object.fromEntries(deps.map((dependency) => [dependency, "workspace:*"])),
+				scripts: name === "pdf" ? {} : Object.fromEntries(tasks.map((task) => [task, "node -e ''"])),
+			}),
+		);
+		lock += `  packages/${name}:`;
+		lock += deps.length
+			? `\n    dependencies:\n${deps.map((dependency) => `      ${dependency}:\n        specifier: workspace:*\n        version: link:../${dependency}\n`).join("")}`
+			: " {}\n";
+	}
+	await writeFile(join(directory, "pnpm-lock.yaml"), lock);
+	baseline = dryRun();
+});
+
+afterAll(async () => {
+	if (directory) await rm(directory, { recursive: true, force: true });
+});
+
+async function withChangedSource(name: string, check: (result: Map<string, DryTask>) => void) {
+	const path = join(directory, "packages", name, "source.ts");
+	const original = await readFile(path);
+	try {
+		await writeFile(path, "export const value = 2;\n");
+		check(dryRun());
+	} finally {
+		await writeFile(path, original);
+	}
+}
+
+it("invalidates every cached consumer task after a transitive source-only package changes", async () => {
+	await withChangedSource("pdf", (result) => {
+		for (const name of ["app", "api"]) {
+			for (const task of tasks) {
+				const id = `${name}#${task}`;
+				expect(result.get(id)?.hash, id).not.toBe(baseline.get(id)?.hash);
+			}
+		}
+	});
+});
+
+it("invalidates direct consumers while retaining unrelated package cache keys", async () => {
+	await withChangedSource("api", (result) => {
+		for (const task of tasks) {
+			expect(result.get(`app#${task}`)?.hash, task).not.toBe(baseline.get(`app#${task}`)?.hash);
+			expect(result.get(`unrelated#${task}`)?.hash, task).toBe(baseline.get(`unrelated#${task}`)?.hash);
+		}
+	});
+});
+
+it("keeps cache keys stable when sources are unchanged", () => {
+	expect(dryRun()).toEqual(baseline);
+});
+
+it("propagates dependency hashes without ordering runnable tasks between packages", () => {
+	for (const task of tasks) {
+		const app = baseline.get(`app#${task}`);
+		expect(app?.dependencies.length, task).toBeGreaterThan(0);
+		const pending = [...(app?.dependencies ?? [])];
+		const visited = new Set<string>();
+		while (pending.length > 0) {
+			const id = pending.pop();
+			if (!id || visited.has(id)) continue;
+			visited.add(id);
+			const dependency = baseline.get(id);
+			expect(dependency?.command, id).toBe("<NONEXISTENT>");
+			pending.push(...(dependency?.dependencies ?? []));
+		}
+	}
+});
diff --git a/turbo.json b/turbo.json
index cf1995e40..5483fe6d1 100644
--- a/turbo.json
+++ b/turbo.json
@@ -90,19 +90,35 @@
 		"FLAG_ALLOW_UNSAFE_AI_BASE_URL"
 	],
 	"tasks": {
+		"transit": {
+			"dependsOn": ["^transit"]
+		},
 		"build": {
 			"inputs": ["$TURBO_DEFAULT$", "$TURBO_ROOT$/.env*"],
-			"outputs": ["dist/**", ".vercel/**"]
+			"outputs": ["dist/**", ".vercel/**"],
+			"dependsOn": ["transit"]
+		},
+		"check": {
+			"dependsOn": ["transit"]
+		},
+		"typecheck": {
+			"dependsOn": ["transit"]
+		},
+		"test": {
+			"dependsOn": ["transit"]
+		},
+		"test:coverage": {
+			"dependsOn": ["transit"]
+		},
+		"test:ci": {
+			"dependsOn": ["transit"]
 		},
-		"check": {},
-		"typecheck": {},
-		"test": {},
-		"test:coverage": {},
-		"test:ci": {},
 		"test:e2e": {
 			"cache": false
 		},
-		"test:agent": {},
+		"test:agent": {
+			"dependsOn": ["transit"]
+		},
 		"dev": {
 			"cache": false,
 			"persistent": true