fix(hermes): disable ACP session/resume by default

Hermes ACP _restore fails for custom providers — resolve_runtime_provider
throws and base_url/api_mode are lost, causing resume to silently create a
new session with no history. Prompt then returns empty text or refusal.

Disable resume by default. Set UWF_HERMES_RESUME=1 to opt back in.

Includes investigation notes in docs/investigations/.

Refs #418

docs/investigations/issue-418-acp-resume.md

@@ -0,0 +1,73 @@
+# Issue #418: ACP session/resume 返回空文本
+
+## 调研日期: 2026-05-23
+
+## 根因
+
+`session/resume` 在 restore 路径下 `_make_agent()` 失败，异常被静默吞掉。
+
+### 完整调用链
+
+```
+resume_session(sid)
+  → update_cwd(sid)
+    → get_session(sid) → _restore(sid)
+      → _make_agent()
+        → resolve_runtime_provider("custom") 失败（line 548-561）
+        → AIAgent() 抛出 "No LLM provider configured"（line 564）
+      → except Exception 静默吞掉（line 482-484）→ return None
+    → return None
+  → state is None → fallback: create_session()（新 sid，无历史）
+```
+
+### 关键代码位置（acp_adapter/session.py）
+
+- `_restore()` line 426-498: 从 DB 恢复 session，但 except 太宽泛
+- `_make_agent()` line 520-568: provider 解析在 restore 路径下不完整
+- Line 548-561: `resolve_runtime_provider("custom")` 失败后，`base_url` 虽然从 DB 取到了但没传给 AIAgent
+
+### 实测行为
+
+1. Phase 1: `session/new` + `prompt` → 正常，有 `agent_message_chunk`
+2. Phase 2: `session/resume` + `prompt`
+   - resume 返回成功，但 `available_commands_update` 里 sessionId 是新的（create_session fallback）
+   - 用原始 sid 发 prompt → `stopReason: "refusal"`（session 不在内存中）
+   - 用新 sid 发 prompt → 能跑但无历史（agent 回答"不知道 secret code"）
+
+### 验证脚本
+
+```python
+# 直接调用 _restore 验证
+cd ~/.hermes/hermes-agent
+python3 -c "
+import sys; sys.path.insert(0, '.')
+from acp_adapter.session import SessionManager
+sm = SessionManager()
+result = sm._restore('SESSION_ID_HERE')
+print(result)  # None — _make_agent 抛异常被吞掉
+"
+```
+
+### 两个 bug
+
+1. **`_make_agent` provider fallback 不完整**: restore 时 DB 里有 `base_url` 和 `api_mode`，但 `resolve_runtime_provider` 失败后这些值没被正确传递给 AIAgent
+2. **`_restore` 的 except 太宽泛**: 静默吞掉所有异常，连 warning 都只在 debug 级别，导致 resume 失败完全无感知
+
+### Hermes 版本
+
+- v0.10.0 (2026.4.16) — 初始测试
+- v0.14.0 (2026.5.16) — 更新后重新测试，bug 仍在
+- 代码路径: ~/.hermes/hermes-agent/acp_adapter/session.py
+
+### v0.14.0 测试结果 (2026-05-23)
+
+- `_restore` 仍因 `custom` provider 解析失败返回 None
+- 日志更清晰了：`WARNING: Failed to recreate agent for ACP session ...`
+- resume fallback 创建新 session（新 sid），但 agent 居然能回答之前的问题（可能通过 memory/session search）
+- 核心问题不变：sessionId 变了，client 用旧 sid 发 prompt → refusal
+
+### 上游 Issue
+
+- https://github.com/NousResearch/hermes-agent/issues/13489 — 已评论根因分析
+- https://github.com/NousResearch/hermes-agent/issues/8083 — resume 静默创建新 session
+- https://github.com/NousResearch/hermes-agent/issues/18452 — _make_agent fallback 不完整

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

@@ -49,8 +49,18 @@ async function writeCache(cache: HermesSessionCache): Promise<void> {
 }
 
 export function isResumeDisabled(): boolean {
-  const flag = process.env.UWF_NO_RESUME;
+  // Hermes ACP session/resume is broken: _restore fails for custom providers
-  return flag !== undefined && flag !== "";
+  // because resolve_runtime_provider("custom") throws and base_url/api_mode
+  // are lost in the fallback path.  Resume silently creates a new session
+  // (different sessionId, no history), causing empty-text responses.
+  // See: https://github.com/NousResearch/hermes-agent/issues/13489
+  // Disable by default until upstream fixes the bug.  Set UWF_HERMES_RESUME=1
+  // to opt back in.
+  const enableFlag = process.env.UWF_HERMES_RESUME;
+  if (enableFlag === "1" || enableFlag === "true") {
+    return false;
+  }
+  return true;
 }
 
 export async function getCachedSessionId(threadId: ThreadId, role: string): Promise<string | null> {