perf: faster plugin updates, half-size first bundle, images from the chat attach on Windows

- Chat view: an attached image's path is pasted on its own after the text
  (promptForPane). claude turns a paste that is only an image path into
  [Image #n], but left a Windows path inside a paste of text as a plain path.
  Other files and @-mentions stay in the text as before.
- Plugin bootstrap: depsHash covers only what npm installs (no release
  version), so a version bump no longer reinstalls runtime deps; the client's
  installed tree is kept while its manifests are unchanged (no npm ci per
  update); the user-side build runs vite only (tsc -b cost ~25 s / ~900 MB);
  clientBuild is recorded only after a build that did not fail, so a failed
  one is retried; npm output goes to runtime/npm-install.log.
- Server: a port held by another program ends with a clear message and exit 1
  instead of an uncaught 'error' stack trace.
- Client: the onboarding wizard is lazy and rendered only before onboarding;
  usePrefersReducedMotion moved to hooks/ so PetSettings no longer pulls the
  Sagi chat/pane stack into the entry chunk (884 KB -> 431 KB, gzip 268 -> 133 KB).

scripts/plugin-open.js

@@ -68,7 +68,19 @@ function buildClient({
   const stdio = logFd === null ? "inherit" : ["ignore", logFd, logFd];
   try {
     const src = path.join(rt, "client-src");
-    fs.rmSync(src, { recursive: true, force: true });
+    // The installed tree is kept across updates while the client's manifests
+    // are unchanged (`stamp`, written after a successful install): a release
+    // rarely touches them, and the clean `npm ci` below fetched all of the
+    // ~200 MB toolchain again on every update.
+    const stamp = path.join(src, "node_modules", ".agenthub-deps");
+    const want = clientDepsHash(root);
+    const reuse = readText(stamp) === want;
+    if (reuse) {
+      for (const e of fs.readdirSync(src))
+        if (e !== "node_modules") fs.rmSync(path.join(src, e), { recursive: true, force: true });
+    } else {
+      fs.rmSync(src, { recursive: true, force: true });
+    }
     fs.cpSync(path.join(root, "client"), src, {
       recursive: true,
       filter: (p) => !/[\\/](node_modules|dist)$/.test(p),
@@ -101,19 +113,25 @@ function buildClient({
     // esbuild is the only dependency with an install script, and it finds its
     // platform binary without it.
     const npmFlags = ["--no-audit", "--no-fund", "--include=dev", "--ignore-scripts"];
-    if (
-      !exec(NPM, ["ci", ...npmFlags], src, stdio) &&
-      !exec(NPM, ["install", ...npmFlags], src, stdio)
-    ) {
-      return "failed";
+    if (!reuse) {
+      if (
+        !exec(NPM, ["ci", ...npmFlags], src, stdio) &&
+        !exec(NPM, ["install", ...npmFlags], src, stdio)
+      ) {
+        return "failed";
+      }
+      fs.mkdirSync(path.dirname(stamp), { recursive: true });
+      fs.writeFileSync(stamp, want);
     }
-    // = client/package.json's "build" script (`tsc -b && vite build`); a test
-    // keeps the two in step.
+    // client/package.json's "build" script is `tsc -b && vite build`; only the
+    // vite half runs here. The type check emits nothing the bundle needs, and on
+    // a user's machine it cost ~25 s and ~900 MB of memory per update — and a
+    // type error in a release then kept the old UI everywhere (v2.7.0). The
+    // release itself still runs `tsc -b`. A test keeps the two in step.
     const bin = (...p) => path.join(src, "node_modules", ...p);
-    if (
-      !exec(NODE, [bin("typescript", "bin", "tsc"), "-b"], src, stdio) ||
-      !exec(NODE, [bin("vite", "bin", "vite.js"), "build"], src, stdio)
-    ) {
+    if (!exec(NODE, [bin("vite", "bin", "vite.js"), "build"], src, stdio)) {
+      // Maybe a damaged kept tree: the next build starts from a clean install.
+      fs.rmSync(stamp, { force: true });
       return "failed";
     }
 
@@ -125,6 +143,22 @@ function buildClient({
   }
 }
 
+function readText(file) {
+  try {
+    return fs.readFileSync(file, "utf8");
+  } catch {
+    return null;
+  }
+}
+
+/** The client's manifests, which decide whether its installed tree still fits. */
+function clientDepsHash(root) {
+  const h = require("crypto").createHash("sha256");
+  for (const f of ["package.json", "package-lock.json"])
+    h.update(readText(path.join(root, "client", f)) ?? `no ${f}`);
+  return h.digest("hex").slice(0, 16);
+}
+
 function dashboardUrl() {
   try {
     return `http://localhost:${resolveDashboardPort()}`;