diff --git a/ARCHITECTURE.md b/ARCHITECTURE.md
index 7f903d60a..3dba8f3ba 100644
--- a/ARCHITECTURE.md
+++ b/ARCHITECTURE.md
@@ -144,6 +144,21 @@ Cookies are the most sensitive data gstack handles. The design:
 
 The browser registry (Comet, Chrome, Arc, Brave, Edge) is hardcoded. Database paths are constructed from known constants, never from user input. Keychain access uses `Bun.spawn()` with explicit argument arrays, not shell string interpolation.
 
+### Unicode sanitization at server egress (v1.38.0.0)
+
+Page content harvested by CDP can contain lone UTF-16 surrogate halves (orphaned high or low surrogates from broken JavaScript string handling on the page). When those reach `JSON.stringify`, Bun emits them as `\uD800`-style escape sequences that the downstream consumer's `JSON.parse` accepts, but the Anthropic API rejects with a 400 — turning a single weird page into a session-killing error. Defense is single-point, applied at every server egress that ships page-derived strings.
+
+| Egress path | Module | Sanitization point |
+|---|---|---|
+| `POST /command` (HTTP) | `browse/src/server.ts` | `handleCommandInternal` wrapper (sanitizes the result of `handleCommandInternalImpl`) |
+| `POST /command/batch` | `browse/src/server.ts` | Same wrapper — batch consumers inherit it |
+| `GET /activity/stream` (SSE) | `browse/src/server.ts` | `sanitizeReplacer` passed to `JSON.stringify` |
+| `GET /inspector/events` (SSE) | `browse/src/server.ts` | `sanitizeReplacer` passed to `JSON.stringify` |
+
+`sanitizeReplacer` is a `JSON.stringify` replacer function that cleans every string value during encoding. Post-stringify regex doesn't work here — `JSON.stringify` has already converted `\uD800` into the literal escape sequence `"\\ud800"` before the regex could match, so the replacer must run inside the encoding pipeline. The pure-string helper `sanitizeLoneSurrogates` is used directly for `text/plain` responses.
+
+**Architectural invariant.** Every new SSE/WebSocket writer or HTTP response that ships page-content-derived strings MUST go through one of two paths: `JSON.stringify(payload, sanitizeReplacer)` for object payloads, or `sanitizeLoneSurrogates(body)` for text bodies. New surfaces that bypass both will desync the system. Inline comments at both SSE producers in `server.ts` say so; `browse/test/server-sanitize-surrogates.test.ts` pins wiring with bug-repro + invariant tests (`handleCommandInternalImpl` rename, central sanitization line, replacer existence, SSE producers stringify with replacer).
+
 ### Prompt injection defense (sidebar agent)
 
 The Chrome sidebar agent has tools (Bash, Read, Glob, Grep, WebFetch) and reads hostile web pages, so it's the part of gstack most exposed to prompt injection. Defense is layered, not single-point.
diff --git a/CLAUDE.md b/CLAUDE.md
index 11d85dc78..6cbff85f9 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -269,6 +269,31 @@ to `~/.gstack/security/attempts.jsonl` via `tunnel-denial-log.ts`. Before editin
 the module boundary (no imports from `token-registry.ts` into `sse-session-cookie.ts`)
 is load-bearing for scope isolation.
 
+**Unicode sanitization at server egress** (v1.38.0.0+). Every server egress that
+ships page-content-derived strings MUST go through `JSON.stringify(payload,
+sanitizeReplacer)` for object payloads or `sanitizeLoneSurrogates(body)` for text
+bodies. Lone UTF-16 surrogate halves from CDP page content otherwise reach the
+Anthropic API as `\uD800`-style escapes and trigger a 400. Wired at four egress
+points today: `handleCommandInternal` (HTTP + batch via a sanitizing wrapper around
+`handleCommandInternalImpl`) and both SSE producers (`/activity/stream`,
+`/inspector/events`). Post-stringify regex is a no-op — `JSON.stringify` has
+already escaped the surrogate before regex could match, so the replacer must run
+inside the encoding pipeline. Before adding a new SSE/WebSocket writer or HTTP
+response in `server.ts`, read
+[ARCHITECTURE.md](ARCHITECTURE.md#unicode-sanitization-at-server-egress-v13800).
+`browse/test/server-sanitize-surrogates.test.ts` pins the wiring with invariant
+tests, so bypasses fail CI.
+
+**Setup symlink hardening** (v1.38.0.0+). Every link site in `setup` MUST route
+through the `_link_or_copy SRC DST` helper near the `IS_WINDOWS` detection. On
+Windows without Developer Mode, plain `ln -snf` produces frozen file copies that
+don't refresh on `git pull` — silent staleness across every host adapter. The
+helper preserves `ln -snf` on Unix and switches to `cp -R` / `cp -f` on Windows.
+`test/setup-windows-fallback.test.ts` enforces a static invariant: a single raw
+`ln` call outside the helper body fails CI. Windows users get a one-line note
+from `_print_windows_copy_note_once` reminding them to re-run `./setup` after
+every `git pull`.
+
 **Sidebar security stack** (layered defense against prompt injection):
 
 | Layer | Module | Lives in |
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 523887510..7f40fa4d8 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -342,6 +342,7 @@ When Conductor creates a new workspace, `bin/dev-setup` runs automatically. It d
 - **Conductor workspaces are independent.** Each workspace is its own git worktree. `bin/dev-setup` runs automatically via `conductor.json`.
 - **`.env` propagates across worktrees.** Set it once in the main repo, all Conductor workspaces get it.
 - **`.claude/skills/` is gitignored.** The symlinks never get committed.
+- **Never write raw `ln -snf` in `setup`.** Every link site in `setup` MUST route through the `_link_or_copy SRC DST` helper near the `IS_WINDOWS` detection. The helper preserves `ln -snf` on Unix and switches to `cp -R` / `cp -f` on Windows without Developer Mode, where plain `ln -snf` produces frozen file copies that don't refresh on `git pull`. `test/setup-windows-fallback.test.ts` enforces this with a static invariant — a single raw `ln` call outside the helper body fails CI.
 
 ## Testing your changes in a real project
 
diff --git a/README.md b/README.md
index 4e2b792ec..54e11ca11 100644
--- a/README.md
+++ b/README.md
@@ -459,6 +459,8 @@ Data is stored in [Supabase](https://supabase.com) (open source Firebase alterna
 
 **Windows users:** gstack works on Windows 11 via Git Bash or WSL. Node.js is required in addition to Bun — Bun has a known bug with Playwright's pipe transport on Windows ([bun#4253](https://github.com/oven-sh/bun/issues/4253)). The browse server automatically falls back to Node.js. Make sure both `bun` and `node` are on your PATH.
 
+On Windows without Developer Mode (MSYS2 / Git Bash), `setup` falls back to file copies instead of symlinks because `ln -snf` produces frozen copies that don't refresh on `git pull`. **Re-run `cd ~/.claude/skills/gstack && ./setup` after every `git pull`** so your skill files match the repo. `setup` prints a one-line note reminding you. Unix and WSL keep symlinks and don't need the re-run.
+
 **Claude says it can't see the skills?** Make sure your project's `CLAUDE.md` has a gstack section. Add this:
 
 ```