diff --git a/docs/IOS_COMPANION_PLAN.md b/docs/IOS_COMPANION_PLAN.md
index a375f67..916eb7b 100644
--- a/docs/IOS_COMPANION_PLAN.md
+++ b/docs/IOS_COMPANION_PLAN.md
@@ -197,6 +197,11 @@ lisa agents pty codex "跑测试"      # codex 同理；--port N 指定非默认
   resume 一个**还活着**的会话会损坏 transcript，端点直接 **409**。`detectClaudeBinary()` 还优先用 app 内置的 claude（版本对得上 transcript）。
 - **入口**：①GUI roster 对 `resumable` 会话给"接管"按钮（#111）；②**终端** `lisa agents pty --resume <session-id>`（本次接通，复用 §4.1 attach 客户端；命中 409 会提示"先关掉它"）；③岛仍保留手动"复制 `claude --resume`"。
 - 覆盖：**用户已起、现已空闲**的 claude 会话："我之前那个会话，手机上让它接着干。"
+- **codex 对等？已查、暂不做（诚实记账，2026-06-19）**：codex CLI **支持续写**（`codex resume <id>`，会话存 `$CODEX_HOME/sessions/YYYY/MM/DD/rollout-*.jsonl`），
+  但 resume-adopt 的 **liveness 守卫对 codex 不成立**——codex **不写 pid 锁**（claude 有 `~/.claude/sessions/<pid>.json`），
+  只能从 rollout 文件 mtime 猜"最近"而非"空闲"，无法防"续写一个还活着的会话 → 双写损坏 transcript"；且 rollout 文件名→resume-id 映射未经证实，本机也无 codex 可验。
+  故 LISA **显式拒绝** codex resume：`PtyAgent.start` 抛错、`POST /api/agents/pty/start` 对非 claude 的 `resumeSessionId` 返回 **400**（旧行为是悄悄起个新会话——已修为诚实拒绝）。
+  codex 的**接管即启**（§4.1，新起）不受影响。解锁条件：codex 给出可靠的 liveness 信号 + 确认 id 映射。详见 [PTY_AGENTS.md](./PTY_AGENTS.md)。
 
 ### 4.3 为什么 tmux / peer 协议不是这里的答案（诚实记账）
 
@@ -211,6 +216,7 @@ lisa agents pty codex "跑测试"      # codex 同理；--port N 指定非默认
 |---|---|---|
 | 我想**新起**一个 claude/codex，且手机可控 | §4.1 接管即启（`lisa agents pty`） | ✅ 已建 |
 | 我**之前起过、现在空闲**的 claude 会话，想接着指挥 | §4.2 resume-adopt（`claude --resume` + liveness 守卫） | ✅ 已落地（#111 后端/GUI + `lisa agents pty --resume`） |
+| 我**之前起过、现在空闲**的 **codex** 会话，想接着指挥 | 暂不支持——codex 无 liveness 信号，无法防双写损坏（§4.2） | ⛔ 已查/显式拒绝（400） |
 | 一个**正在跑**的桌面 app / IDE 会话 | **不可控**，只能观察；等它空闲再 §4.2 | —— |
 
 **iOS 侧零特判**：两条可行路都产出 `controllable:"pty"` + 现成 `/api/agents/pty/*`。app 控制 UI 仍只 key off `controllable`，
diff --git a/docs/PTY_AGENTS.md b/docs/PTY_AGENTS.md
index 3602cd5..89ff01e 100644
--- a/docs/PTY_AGENTS.md
+++ b/docs/PTY_AGENTS.md
@@ -41,6 +41,40 @@ owns its stdin/stdout), but every session has a stable `sessionId`, and
 - Binary: LISA resumes with `LISA_PTY_CLAUDE_CMD` → the newest app-bundled
   `claude` (version-matched to your sessions) → PATH `claude`.
 
+## Why codex resume-adopt isn't supported (yet)
+
+Resume-adopt is **claude-only by design** — not an oversight. The codex CLI *does*
+support continuation (`codex resume <session-id> [prompt]`; sessions live at
+`$CODEX_HOME/sessions/YYYY/MM/DD/rollout-*.jsonl`), so in principle LISA could spawn
+`codex resume <id>` under a PTY the same way it spawns `claude --resume <id>`. The
+blocker is **safety, not capability**:
+
+- **No liveness signal.** The adopt guard refuses resuming a session that's still
+  *live* — two writers to one JSONL transcript interleave and corrupt it. For claude
+  we read `~/.claude/sessions/<pid>.json` and `kill -0` the owning pid
+  (`liveClaudeSessionIds()`): an authoritative "is it running right now?" check. Codex
+  leaves **no equivalent** — its rollout carries no pid/lock, and the observer can
+  only infer "recent" from file mtime, which is *not* "idle". An mtime heuristic
+  would let a paused-but-live session look adoptable and then get corrupted —
+  precisely what the guard must prevent.
+- **Unverified id mapping.** Our observer derives a codex `sessionId` from the rollout
+  filename (`rollout-<id>.jsonl` → `<id>`); whether that's the exact token
+  `codex resume <id>` wants is unconfirmed, and codex isn't installed here to check.
+- **Can't be exercised here.** node-pty won't spawn under Node 26 (see the local-dev
+  caveat), so a speculative implementation couldn't be verified end-to-end anyway.
+
+Rather than ship a guessed, unguarded path on a transcript-**corruption** surface,
+LISA refuses codex resume explicitly: `PtyAgent.start` throws, and
+`POST /api/agents/pty/start` returns **400** when `resumeSessionId` is set for a
+non-claude agent. (It previously dropped the id silently and started a *fresh*
+session — honest-by-refusal beats silently-wrong.) codex **adopt-at-launch**
+(`lisa agents pty codex "<task>"`, a brand-new session) is unaffected and works.
+
+**What would unblock it:** a reliable codex liveness check — codex writing a pid/lock
+we can `kill -0`, or an `is-live` signal it exposes — plus a confirmed
+rollout→resume-id mapping. Then the guard generalizes and the PTY arg-builder simply
+adds the `codex resume <id>` form.
+
 ## Enabling it
 
 1. Install the optional native dep (it has zero JS deps; if your machine can't
@@ -112,7 +146,7 @@ a full arrow-key TUI. Raw attach is future work.
 | Method + path | Body | Effect |
 | --- | --- | --- |
 | `POST /api/agents/pty/start` | `{ agent, task, cwd? }` | spawn a fresh PTY agent (503 if flag off) |
-| `POST /api/agents/pty/start` | `{ agent:"claude", resumeSessionId, cwd? }` | **adopt** an idle session (409 if it's live) |
+| `POST /api/agents/pty/start` | `{ agent:"claude", resumeSessionId, cwd? }` | **adopt** an idle session (claude-only: **400** for other agents; **409** if it's live) |
 | `POST /api/agents/pty/<id>/send` | `{ text }` | type a line into the CLI |
 | `POST /api/agents/pty/<id>/cancel` | — | kill the CLI |
 | `GET /api/agents/pty/<id>/output` | — | ANSI-stripped terminal tail (one-shot) |
diff --git a/src/agents/pty.test.ts b/src/agents/pty.test.ts
index 0000372..617713e 100644
--- a/src/agents/pty.test.ts
+++ b/src/agents/pty.test.ts
@@ -37,8 +37,10 @@ function fakePty() {
   };
   let spawnFile = "";
   let spawnArgs: string[] = [];
+  let spawnCount = 0;
   const module: PtyModuleLike = {
     spawn: (file, args) => {
+      spawnCount++;
       spawnFile = file;
       spawnArgs = args;
       return proc;
@@ -51,6 +53,9 @@ function fakePty() {
     emitExit: (code: number) => exitCb?.({ exitCode: code }),
     isKilled: () => killed,
     getSpawn: () => ({ file: spawnFile, args: spawnArgs }),
+    get spawnCount() {
+      return spawnCount;
+    },
   };
 }
 
@@ -173,12 +178,18 @@ test("resumeSessionId adopts an existing session via `--resume <id>`", async ()
   });
 });
 
-test("resume is claude-only (codex ignores resumeSessionId)", async () => {
+test("resume-adopt is claude-only — codex resume is refused, not silently downgraded", async () => {
   await withFlag(async () => {
     const f = fakePty();
     const reg = new PtyRegistry();
-    await reg.start({ agent: "codex", task: "", cwd: "/tmp/p", resumeSessionId: "abc-123", cli: "codex", ptyModule: f.module });
-    assert.equal(f.getSpawn().args.includes("--resume"), false);
+    // Codex has no liveness signal, so adopting one can't be guarded against
+    // transcript corruption. Refusing (vs. silently starting a fresh session)
+    // keeps the API honest. See docs/PTY_AGENTS.md.
+    await assert.rejects(
+      () => reg.start({ agent: "codex", task: "", cwd: "/tmp/p", resumeSessionId: "abc-123", cli: "codex", ptyModule: f.module }),
+      /only supported for claude/i,
+    );
+    assert.equal(f.spawnCount, 0); // never spawned anything
   });
 });
 
diff --git a/src/agents/pty.ts b/src/agents/pty.ts
index 77c3d7e..eef10de 100644
--- a/src/agents/pty.ts
+++ b/src/agents/pty.ts
@@ -241,9 +241,22 @@ export class PtyAgent {
       throw new Error("node-pty is not installed — run `npm i node-pty` to enable PTY agents");
     }
     const kind = normalizeAgentKind(opts.agent);
+    // Resume-adopt is claude-only. The codex CLI *does* support `codex resume
+    // <id>`, but LISA can't adopt it SAFELY: unlike claude (which writes
+    // ~/.claude/sessions/<pid>.json), codex leaves no liveness signal, so we
+    // can't tell whether a rollout is idle vs. open right now — and resuming a
+    // live session double-writes its transcript and corrupts it. Refuse rather
+    // than silently dropping the id and spawning a fresh session. See
+    // docs/PTY_AGENTS.md ("Why codex resume-adopt isn't supported (yet)").
+    if (opts.resumeSessionId && kind !== "claude-code") {
+      throw new Error(
+        `resume-adopt is only supported for claude sessions (got "${opts.agent}") — ` +
+          "codex has no liveness signal to guard against transcript corruption",
+      );
+    }
     const cli = opts.cli ?? (kind === "claude-code" ? detectClaudeBinary() : resolveCli(opts.agent));
-    // Adopt an existing session by id (claude only): `claude --resume <id>`.
-    const resumeArgs = opts.resumeSessionId && kind === "claude-code" ? ["--resume", opts.resumeSessionId] : [];
+    // Adopt an existing session by id: `claude --resume <id>` (claude-only, guarded above).
+    const resumeArgs = opts.resumeSessionId ? ["--resume", opts.resumeSessionId] : [];
     const args = [...resumeArgs, ...(opts.args ?? [])];
     const now = opts.now ?? Date.now;
     const proc = pty.spawn(cli, args, {
diff --git a/src/web/server.ts b/src/web/server.ts
index 5a32a67..0a85f1b 100644
--- a/src/web/server.ts
+++ b/src/web/server.ts
@@ -37,7 +37,7 @@ import { polishDictation, type DictationProvider } from "../voice/dictation.js";
 import { listGrants, grant, revoke, revokeAll, isGranted, SENSE_SIGNALS, SIGNAL_DESCRIPTIONS } from "../consent/store.js";
 import { signalAgentTool } from "../tools/signal_agent.js";
 import { managedRegistry } from "../agents/managed.js";
-import { ptyRegistry, ptyEnabled } from "../agents/pty.js";
+import { ptyRegistry, ptyEnabled, normalizeAgentKind } from "../agents/pty.js";
 import { liveClaudeSessionIds } from "../integrations/claude-code/liveness.js";
 import { listRecentDispatches, isAlive, toDispatchView, readDispatchOutput } from "../integrations/dispatch-ledger.js";
 import { loadControlPolicy, saveControlPolicy, type ControlPolicy } from "../control/policy.js";
@@ -1043,6 +1043,14 @@ export async function startWebServer(opts: WebServerOptions): Promise<http.Serve
       // Adopting an external session is the highest-risk control action — gate it
       // behind remoteAdoptExternal; starting a fresh agent is ordinary control.
       if (denyRemote(resumeSessionId ? "adoptExternal" : "control")) return;
+      // Resume-adopt is claude-only (docs/PTY_AGENTS.md). Codex has no liveness
+      // signal, so we can't guard against resuming a *live* rollout and corrupting
+      // it — refuse with a clear 400 rather than silently spawning a fresh session.
+      if (resumeSessionId && normalizeAgentKind(agent) !== "claude-code") {
+        res.writeHead(400, { "content-type": "text/plain" });
+        res.end(`resume-adopt is only supported for claude sessions (got "${agent}"); start a fresh agent instead`);
+        return;
+      }
       // Adopting an existing session needs no task (it continues the convo); a
       // fresh agent does. Guard: never resume a session that's currently live.
       if (!resumeSessionId && (typeof payload.task !== "string" || !payload.task.trim())) {