fix(server): ignore sibling worktrees in dev watch (#11074)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Developers can run Paperclip from linked Git worktrees.
> - The server development watcher scans paths near the active checkout.
> - A main checkout can contain many complete sibling worktrees under
`.paperclip/worktrees`.
> - Scanning those sibling checkouts can stall the watcher before it
starts the server.
> - This pull request excludes the shared worktree directory from the
development watcher.
> - The benefit is that development startup stays responsive as the
number of worktrees grows.

## Linked Issues or Issue Description

**What happened?**

The server development watcher traversed sibling checkouts under
`.paperclip/worktrees`. Large worktree collections could make `pnpm dev`
stall before the watcher started the server process.

**Expected behavior**

The watcher must observe only source paths that can reload the active
checkout. It must ignore sibling worktrees in both a main checkout and a
linked worktree.

**Steps to reproduce**

1. Create several linked worktrees under `.paperclip/worktrees`.
2. Add normal dependency and build output trees to those worktrees.
3. Run `pnpm dev` from the main checkout or one linked worktree.
4. Observe the watcher scan sibling worktrees before it starts the
server.

**Paperclip version or commit**

Reproduced on `master` before this change.

**Deployment mode**

Local development with `pnpm dev`.

## What Changed

- Detect whether the active server root is inside the managed
linked-worktree directory.
- Ignore the shared `.paperclip/worktrees` root from both main and
linked checkouts.
- Add regression coverage for the resolved ignore path and its globstar
form.

## Verification

- `./node_modules/.bin/vitest run
server/src/__tests__/dev-watch-ignore.test.ts --reporter=verbose`
- `pnpm --filter @paperclipai/server typecheck`

## Risks

- Low risk. The change affects only local development watch exclusions.
- A non-standard checkout that copies the same `.paperclip/worktrees`
directory layout will receive the same exclusion.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5, context window not disclosed, with reasoning,
tool use, and code execution.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/__tests__/dev-watch-ignore.test.ts

@@ -36,6 +36,9 @@ describe("resolveServerDevWatchIgnorePaths", () => {
     expect(ignorePaths).toContain(fs.realpathSync(path.join(sharedUiRoot, ".vite")));
     expect(ignorePaths).toContain(path.join(worktreeUiRoot, "dist"));
     expect(ignorePaths).toContain(fs.realpathSync(path.join(sharedUiRoot, "dist")));
+    const sharedWorktreesRoot = path.join(tempRoot, "repo", ".paperclip", "worktrees");
+    expect(ignorePaths).toContain(sharedWorktreesRoot);
+    expect(ignorePaths).toContain(`${sharedWorktreesRoot.replaceAll(path.sep, "/")}/**`);
     expect(ignorePaths).toContain("**/{node_modules,bower_components,vendor}/**");
     expect(ignorePaths).toContain("**/.vite-temp/**");
   });

server/src/dev-watch-ignore.ts

@@ -18,6 +18,11 @@ function addIgnorePath(target: Set<string>, candidate: string): void {
 }
 
 export function resolveServerDevWatchIgnorePaths(serverRoot: string): string[] {
+  const checkoutRoot = path.dirname(serverRoot);
+  const linkedWorktreesRoot = path.dirname(checkoutRoot);
+  const isLinkedWorktree =
+    path.basename(linkedWorktreesRoot) === "worktrees" &&
+    path.basename(path.dirname(linkedWorktreesRoot)) === ".paperclip";
   const ignorePaths = new Set<string>([
     "**/{node_modules,bower_components,vendor}/**",
     "**/.vite-temp/**",
@@ -28,6 +33,14 @@ export function resolveServerDevWatchIgnorePaths(serverRoot: string): string[] {
     "../ui/node_modules/.vite-temp",
     "../ui/.vite",
     "../ui/dist",
+    // Git worktrees live under <repo>/.paperclip/worktrees, each a full
+    // checkout (source + its own .paperclip). Watching them can add hundreds
+    // of thousands of files, stalling tsx watch before it ever spawns the
+    // server. None of them are part of this checkout's reloadable source.
+    // A linked checkout has serverRoot at
+    // <repo>/.paperclip/worktrees/<branch>/server. In that case, the shared
+    // worktree directory is the checkout's parent, not a nested path.
+    isLinkedWorktree ? "../.." : "../.paperclip/worktrees",
     // npm install during reinstall would trigger a restart mid-request
     // if tsx watch sees the new files. Exclude the managed plugins dir.
     process.env.HOME + "/.paperclip/adapter-plugins",