fix(agent-kit): separate session cache per agent

Each agent now maintains its own session cache file instead of sharing
a single agent-sessions.json. This prevents session ID conflicts when
multiple agents operate on the same thread+role pair.

Changes:
- getCachePath() now takes agentName parameter
- getCachedSessionId/setCachedSessionId require agentName as first param
- Cache files named <agent>-sessions.json (e.g., hermes-sessions.json)
- Agent wrappers inject their agent name into cache calls
- Add comprehensive tests for session cache isolation
- Handle malformed JSON gracefully (treat as empty cache)

Fixes #461

packages/workflow-agent-kit/__tests__/session-cache.test.ts

@@ -0,0 +1,247 @@
+import { mkdir, readdir, readFile, rm, stat, writeFile } from "node:fs/promises";
+import { dirname, join } from "node:path";
+import type { ThreadId } from "@uncaged/workflow-protocol";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+
+import { getCachedSessionId, getCachePath, setCachedSessionId } from "../src/session-cache.js";
+import { resolveStorageRoot } from "../src/storage.js";
+
+describe("session-cache", () => {
+  let originalStorageRoot: string;
+  let testStorageRoot: string;
+
+  beforeEach(async () => {
+    // Create a temporary test storage root
+    originalStorageRoot = resolveStorageRoot();
+    testStorageRoot = join(originalStorageRoot, "test-cache", `test-${Date.now()}`);
+    await mkdir(testStorageRoot, { recursive: true });
+
+    // Override the storage root for testing
+    process.env.WORKFLOW_STORAGE_ROOT = testStorageRoot;
+  });
+
+  afterEach(async () => {
+    // Clean up test storage root
+    await rm(testStorageRoot, { recursive: true, force: true });
+    delete process.env.WORKFLOW_STORAGE_ROOT;
+  });
+
+  describe("getCachePath", () => {
+    test("returns agent-specific file path", () => {
+      const path = getCachePath("claude-code");
+      expect(path).toMatch(/\/cache\/claude-code-sessions\.json$/);
+    });
+
+    test("returns different paths for different agents", () => {
+      const pathClaudeCode = getCachePath("claude-code");
+      const pathHermes = getCachePath("hermes");
+
+      expect(pathClaudeCode).not.toBe(pathHermes);
+      expect(pathClaudeCode).toMatch(/claude-code-sessions\.json$/);
+      expect(pathHermes).toMatch(/hermes-sessions\.json$/);
+    });
+
+    test("handles agent names with special characters", () => {
+      const path1 = getCachePath("my-agent");
+      const path2 = getCachePath("my_agent");
+
+      expect(path1).toMatch(/my-agent-sessions\.json$/);
+      expect(path2).toMatch(/my_agent-sessions\.json$/);
+    });
+  });
+
+  describe("session isolation", () => {
+    const threadId = "01234567890123456789012345" as ThreadId;
+    const role = "developer";
+
+    test("sessions are isolated per agent", async () => {
+      // Cache different session IDs for each agent
+      await setCachedSessionId("claude-code", threadId, role, "session-cc-001");
+      await setCachedSessionId("hermes", threadId, role, "session-hermes-001");
+
+      // Each agent should retrieve its own session ID
+      const sessionCC = await getCachedSessionId("claude-code", threadId, role);
+      const sessionHermes = await getCachedSessionId("hermes", threadId, role);
+
+      expect(sessionCC).toBe("session-cc-001");
+      expect(sessionHermes).toBe("session-hermes-001");
+    });
+
+    test("updating one agent's cache does not affect another", async () => {
+      // Set initial sessions for both agents
+      await setCachedSessionId("claude-code", threadId, role, "session-cc-001");
+      await setCachedSessionId("hermes", threadId, role, "session-hermes-001");
+
+      // Update claude-code's session
+      await setCachedSessionId("claude-code", threadId, role, "session-cc-002");
+
+      // Hermes's session should remain unchanged
+      const sessionHermes = await getCachedSessionId("hermes", threadId, role);
+      expect(sessionHermes).toBe("session-hermes-001");
+
+      // Claude-code should have the new session
+      const sessionCC = await getCachedSessionId("claude-code", threadId, role);
+      expect(sessionCC).toBe("session-cc-002");
+    });
+
+    test("missing session returns null for specific agent", async () => {
+      const session = await getCachedSessionId("claude-code", threadId, role);
+      expect(session).toBeNull();
+    });
+
+    test("empty session ID is treated as missing", async () => {
+      await setCachedSessionId("claude-code", threadId, role, "");
+
+      const session = await getCachedSessionId("claude-code", threadId, role);
+      expect(session).toBeNull();
+    });
+  });
+
+  describe("file system operations", () => {
+    const threadId = "01234567890123456789012345" as ThreadId;
+    const role = "developer";
+
+    test("cache directory is created if missing", async () => {
+      const cachePath = getCachePath("claude-code");
+      const cacheDir = dirname(cachePath);
+
+      // Ensure cache dir doesn't exist
+      await rm(cacheDir, { recursive: true, force: true });
+
+      // Write a session
+      await setCachedSessionId("claude-code", threadId, role, "session-001");
+
+      // Cache directory should be created
+      const stats = await stat(cacheDir);
+      expect(stats.isDirectory()).toBe(true);
+    });
+
+    test("multiple agents create separate cache files", async () => {
+      // Cache sessions for multiple agents
+      await setCachedSessionId("claude-code", threadId, role, "session-cc-001");
+      await setCachedSessionId("hermes", threadId, role, "session-hermes-001");
+
+      // Separate cache files should exist
+      const pathCC = getCachePath("claude-code");
+      const pathHermes = getCachePath("hermes");
+
+      const contentCC = JSON.parse(await readFile(pathCC, "utf8")) as Record<string, string>;
+      const contentHermes = JSON.parse(await readFile(pathHermes, "utf8")) as Record<
+        string,
+        string
+      >;
+
+      expect(contentCC).toHaveProperty(`${threadId}:${role}`, "session-cc-001");
+      expect(contentHermes).toHaveProperty(`${threadId}:${role}`, "session-hermes-001");
+    });
+
+    test("atomic writes prevent partial reads", async () => {
+      // Write a session
+      await setCachedSessionId("claude-code", threadId, role, "session-001");
+
+      // The final file should exist (no .tmp files left behind)
+      const cachePath = getCachePath("claude-code");
+      const dir = dirname(cachePath);
+      const files = await readdir(dir);
+
+      expect(files).toContain("claude-code-sessions.json");
+      expect(files.every((f) => !f.endsWith(".tmp"))).toBe(true);
+    });
+  });
+
+  describe("legacy migration", () => {
+    const threadId = "01234567890123456789012345" as ThreadId;
+    const role = "developer";
+
+    test("old agent-sessions.json is ignored", async () => {
+      // Create old agent-sessions.json file
+      const oldCachePath = join(resolveStorageRoot(), "cache", "agent-sessions.json");
+      await mkdir(dirname(oldCachePath), { recursive: true });
+      await writeFile(
+        oldCachePath,
+        JSON.stringify({
+          "01234567890123456789012345:developer": "old-session-001",
+        }),
+        "utf8",
+      );
+
+      // Query with the new per-agent cache
+      const session = await getCachedSessionId("claude-code", threadId, role);
+
+      // Should return null (old cache is ignored)
+      expect(session).toBeNull();
+    });
+
+    test("new per-agent cache takes precedence", async () => {
+      // Create both old and new cache files
+      const oldPath = join(resolveStorageRoot(), "cache", "agent-sessions.json");
+      await mkdir(dirname(oldPath), { recursive: true });
+      await writeFile(
+        oldPath,
+        JSON.stringify({
+          [`${threadId}:${role}`]: "old-session",
+        }),
+        "utf8",
+      );
+
+      await setCachedSessionId("claude-code", threadId, role, "new-session");
+
+      // The new per-agent cache value should be returned
+      const session = await getCachedSessionId("claude-code", threadId, role);
+      expect(session).toBe("new-session");
+    });
+  });
+
+  describe("error handling", () => {
+    const threadId = "01234567890123456789012345" as ThreadId;
+    const role = "developer";
+
+    test("invalid JSON in cache file returns empty cache", async () => {
+      // Create a corrupted cache file
+      const cachePath = getCachePath("claude-code");
+      await mkdir(dirname(cachePath), { recursive: true });
+      await writeFile(cachePath, "{ invalid json }", "utf8");
+
+      // Should return null (treating corrupted cache as empty)
+      const session = await getCachedSessionId("claude-code", threadId, role);
+      expect(session).toBeNull();
+    });
+
+    test("non-object JSON in cache file returns empty cache", async () => {
+      // Create a cache file with non-object JSON
+      const cachePath = getCachePath("claude-code");
+      await mkdir(dirname(cachePath), { recursive: true });
+      await writeFile(cachePath, JSON.stringify(["not", "an", "object"]), "utf8");
+
+      // Should return null
+      const session = await getCachedSessionId("claude-code", threadId, role);
+      expect(session).toBeNull();
+    });
+
+    test("cache entries with non-string values are ignored", async () => {
+      // Create a cache file with mixed types
+      const cachePath = getCachePath("claude-code");
+      const cacheData = {
+        "thread1:role1": "valid-session",
+        "thread2:role2": 12345, // number
+        "thread3:role3": null, // null
+        "thread4:role4": "", // empty string
+      };
+      await mkdir(dirname(cachePath), { recursive: true });
+      await writeFile(cachePath, JSON.stringify(cacheData), "utf8");
+
+      // Valid string entries should be returned
+      const session1 = await getCachedSessionId("claude-code", "thread1" as ThreadId, "role1");
+      expect(session1).toBe("valid-session");
+
+      // Invalid entries should return null
+      const session2 = await getCachedSessionId("claude-code", "thread2" as ThreadId, "role2");
+      const session3 = await getCachedSessionId("claude-code", "thread3" as ThreadId, "role3");
+      const session4 = await getCachedSessionId("claude-code", "thread4" as ThreadId, "role4");
+
+      expect(session2).toBeNull();
+      expect(session3).toBeNull();
+      expect(session4).toBeNull(); // empty string is treated as missing
+    });
+  });
+});

packages/workflow-agent-kit/src/index.ts

@@ -12,7 +12,7 @@ export {
 export type { FrontmatterFastPathResult } from "./frontmatter.js";
 export { tryFrontmatterFastPath } from "./frontmatter.js";
 export { createAgent } from "./run.js";
-export { getCachedSessionId, setCachedSessionId } from "./session-cache.js";
+export { getCachedSessionId, getCachePath, setCachedSessionId } from "./session-cache.js";
 export { getConfigPath, getEnvPath, loadWorkflowConfig, resolveStorageRoot } from "./storage.js";
 export type {
   AgentContext,

packages/workflow-agent-kit/src/session-cache.ts

@@ -8,8 +8,8 @@ import { resolveStorageRoot } from "./storage.js";
 
 type SessionCache = Record<string, string>;
 
-function getCachePath(): string {
-  return join(resolveStorageRoot(), "cache", "agent-sessions.json");
+export function getCachePath(agentName: string): string {
+  return join(resolveStorageRoot(), "cache", `${agentName}-sessions.json`);
 }
 
 function cacheKey(threadId: ThreadId, role: string): string {
@@ -20,8 +20,8 @@ function isRecord(value: unknown): value is Record<string, unknown> {
   return typeof value === "object" && value !== null && !Array.isArray(value);
 }
 
-async function readCache(): Promise<SessionCache> {
-  const path = getCachePath();
+async function readCache(agentName: string): Promise<SessionCache> {
+  const path = getCachePath(agentName);
   try {
     const text = await readFile(path, "utf8");
     const raw = JSON.parse(text) as unknown;
@@ -40,36 +40,45 @@ async function readCache(): Promise<SessionCache> {
     if (err.code === "ENOENT") {
       return {};
     }
+    // Treat JSON parse errors as empty cache
+    if (err.name === "SyntaxError") {
+      return {};
+    }
     throw e;
   }
 }
 
-async function writeCache(cache: SessionCache): Promise<void> {
-  const path = getCachePath();
+async function writeCache(agentName: string, cache: SessionCache): Promise<void> {
+  const path = getCachePath(agentName);
   const dir = dirname(path);
   await mkdir(dir, { recursive: true });
   // Atomic write: write to temp file then rename to avoid partial reads on concurrent access.
   // NOTE: Current workflow execution is serial (execFileSync), so true concurrency doesn't occur.
   // This is a safety net for future parallel execution.
-  const tmpPath = join(dir, `.agent-sessions.${randomBytes(4).toString("hex")}.tmp`);
+  const tmpPath = join(dir, `.${agentName}-sessions.${randomBytes(4).toString("hex")}.tmp`);
   await writeFile(tmpPath, `${JSON.stringify(cache, null, 2)}\n`, "utf8");
   await rename(tmpPath, path);
 }
 
 /** Read the cached session ID for a thread+role pair. */
-export async function getCachedSessionId(threadId: ThreadId, role: string): Promise<string | null> {
-  const cache = await readCache();
+export async function getCachedSessionId(
+  agentName: string,
+  threadId: ThreadId,
+  role: string,
+): Promise<string | null> {
+  const cache = await readCache(agentName);
   const sessionId = cache[cacheKey(threadId, role)];
   return sessionId ?? null;
 }
 
 /** Write the session ID for a thread+role pair into the cache. */
 export async function setCachedSessionId(
+  agentName: string,
   threadId: ThreadId,
   role: string,
   sessionId: string,
 ): Promise<void> {
-  const cache = await readCache();
+  const cache = await readCache(agentName);
   cache[cacheKey(threadId, role)] = sessionId;
-  await writeCache(cache);
+  await writeCache(agentName, cache);
 }