docs: extend the instance-isolation rule to tmux socket resolution

The data-dir half was already spelled out; the socket half only lived in
a function docstring, and the TUI is the first code that shells out to
`tmux -L` from a process that is not the server.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CLAUDE.md

@@ -132,7 +132,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 - **Zod `.optional()` rejects `null`** — accepts `undefined` only. When the frontend builds a request body with `JSON.stringify`, an explicit `null` field is preserved on the wire and fails validation with `INVALID_INPUT`. Convert `null` → `undefined` before stringifying (e.g. `field: value ?? undefined`), or declare the schema `.nullish()`. This has caused real shipped bugs twice
 - **`xterm-zerolag-input` is single-source** — BOTH echo addons live ONLY in `packages/xterm-zerolag-input/src/`, bundled into TWO **gitignored** vendor files: `vendor/xterm-zerolag-input.js` (buffer overlay, entry `zerolag-input-addon.ts`) and `vendor/xterm-predictive-echo.js` (codex write-through, entry `predictive-echo-addon.ts`) — dev by `scripts/postinstall.js`, prod by `scripts/build.mjs`. `app.js`/terminal-ui.js only **consume** them via `new LocalEchoOverlay(terminal)` / `new PredictiveEchoOverlay(terminal)`; there is no inline copy. So: change the package source, then rerun the bundle step (`npm install` for dev, `npm run build` for prod). **Never hand-edit `app.js` for overlay behavior, and never commit the gitignored vendor bundles.** Always test on mobile after touching it. → [architecture-invariants#xterm-zerolag-input-is-single-source](docs/architecture-invariants.md#xterm-zerolag-input-is-single-source), `docs/local-echo-overlay-plan.md`
 - **Default bind is loopback-only; non-loopback without a password starts but warns** — the server defaults to `--host 127.0.0.1`. Binding non-loopback (`--host`/`-H`/`CODEMAN_HOST`) without `CODEMAN_PASSWORD` starts anyway but prints a loud warning; `--allow-unauthenticated-network` / `CODEMAN_ALLOW_UNAUTHENTICATED_NETWORK=1` acknowledges it. ⚠️ The production systemd unit passes no `--host`, so prod binds **localhost only**: reach it via `tailscale serve`/tunnel to `127.0.0.1`. A loopback bind is reachable through a same-host tunnel but NOT by a browser hitting the box's LAN IP. `install.sh` is separate and prompts for the binding (defaulting to LAN + a password), and preserves the existing binding on re-runs. → [architecture-invariants#default-bind-and-the-non-loopback-warning-path](docs/architecture-invariants.md#default-bind-and-the-non-loopback-warning-path), `docs/security-architecture.md`
-- **Instance isolation / multi-instance attach danger** — the data dir (`~/.codeman`) and tmux socket (`tmux -L codeman`) are PROCESS-WIDE and shared by every Codeman on the machine, derived from `CODEMAN_INSTANCE` via `src/config/instance.ts`. ⚠️ A 2nd instance on the SAME socket **discovers and attaches PTYs to the first instance's live sessions**, resizing and mutating them. `$HOME` isolation is NOT enough because tmux is system-global. To run two instances, give each a distinct `CODEMAN_INSTANCE` (scopes dir + socket together), or set `CODEMAN_TMUX_SOCKET` + `CODEMAN_DATA_DIR` individually; `scripts/run-beta.sh` does this for a beta alongside prod. **Any new `~/.codeman/...` path MUST go through `dataPath()`**, never `join(homedir(), '.codeman', …)`. → [architecture-invariants#instance-isolation-and-the-multi-instance-attach-danger](docs/architecture-invariants.md#instance-isolation-and-the-multi-instance-attach-danger)
+- **Instance isolation / multi-instance attach danger** — the data dir (`~/.codeman`) and tmux socket (`tmux -L codeman`) are PROCESS-WIDE and shared by every Codeman on the machine, derived from `CODEMAN_INSTANCE` via `src/config/instance.ts`. ⚠️ A 2nd instance on the SAME socket **discovers and attaches PTYs to the first instance's live sessions**, resizing and mutating them. `$HOME` isolation is NOT enough because tmux is system-global. To run two instances, give each a distinct `CODEMAN_INSTANCE` (scopes dir + socket together), or set `CODEMAN_TMUX_SOCKET` + `CODEMAN_DATA_DIR` individually; `scripts/run-beta.sh` does this for a beta alongside prod. **Any new `~/.codeman/...` path MUST go through `dataPath()`**, never `join(homedir(), '.codeman', …)`, and **any new `tmux -L` caller through `resolveTmuxSocketName()`** (both in `config/instance.ts`): the TUI shells out to tmux from a second process, and a hardcoded `codeman` there would point a beta instance at prod's panes. → [architecture-invariants#instance-isolation-and-the-multi-instance-attach-danger](docs/architecture-invariants.md#instance-isolation-and-the-multi-instance-attach-danger)
 - **node-pty's macOS `spawn-helper` ships without `+x`** (issues #6, #204): `node-pty@1.1.0` publishes `prebuilds/darwin-<arch>/spawn-helper` as mode 0644, and macOS launches every PTY through it, so a stock macOS install fails every session start with `Error: posix_spawnp failed.` **Linux can never reproduce it**: `spawn-helper` is an `OS=="mac"` gyp target and node-pty ships no Linux prebuild, so node-gyp always emits an executable helper there. ⚠️ Look in **`prebuilds/<platform>-<arch>/`**, not just `build/Release/`, which does not exist on macOS. Repair is a chmod, never a mandatory rebuild (that would require Xcode CLI tools and deletes `prebuilds/` before compiling): `npm run fix:node-pty` chmods every helper then proves it by really opening a PTY. `spawnPtyWithHelperRepair()` (`utils/node-pty-repair.ts`) wraps every `pty.spawn()` in `session.ts` and self-heals a broken install on the first failure. → [architecture-invariants#node-ptys-macos-spawn-helper-must-be-executable](docs/architecture-invariants.md#node-ptys-macos-spawn-helper-must-be-executable)
 - **Headless screenshots: `deviceScaleFactor` MUST be 1, and write unique filenames** — under DSF=2 xterm's WebGL renderer draws glyphs at ~2× nominal size while still *reporting* nominal cell dims, so only the pixels reveal it and only the terminal font looks wrong. And overwriting a fixed output path leaves OS image viewers showing the old render, which reads as "the fix didn't work"; `scripts/capture-real-overview.mjs` mints a timestamped filename per run. Seed the per-device `localStorage` keys (`codeman:skin`, `codeman-font-size`, `codeman-app-settings`) so the capture matches a real device. → [architecture-invariants#headless-screenshot-capture](docs/architecture-invariants.md#headless-screenshot-capture)