diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ee101e0eb..d405c2504 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -14,6 +14,8 @@ bun install                    # install dependencies
 bin/dev-setup                  # activate dev mode
 ```
 
+`./setup` on its own installs production dependencies only. `bun install` (and `bin/dev-setup`, which runs it) adds the dev toolchain the tests and evals need: the Claude Agent SDK, TypeScript and Prettier. A later `./setup` never removes them.
+
 > **Full clone vs shallow.** The README's user-facing install uses `--depth 1` for speed. As a contributor, use a full clone (no `--depth` flag) — you'll need history for `git log`, `git blame`, `git bisect`, and reviewing PRs against earlier versions. If you already have a `--depth 1` clone from following the README, promote it to a full clone with `git fetch --unshallow`.
 
 ### First free check (no API key, no browser)
diff --git a/bin/dev-setup b/bin/dev-setup
index 4079e5cc4..f77026715 100755
--- a/bin/dev-setup
+++ b/bin/dev-setup
@@ -22,11 +22,11 @@ if [ ! -f "$REPO_ROOT/.env" ]; then
   fi
 fi
 
-# 2. Install dependencies
-if [ ! -d "$REPO_ROOT/node_modules" ]; then
-  echo "Installing dependencies..."
-  (cd "$REPO_ROOT" && bun install)
-fi
+# 2. Install dependencies, devDependencies included. Always run: a checkout
+# first installed by ./setup has production dependencies only, and an
+# up-to-date install is a no-op.
+echo "Installing dependencies..."
+(cd "$REPO_ROOT" && bun install)
 
 # 3. Create .claude/skills/ inside the repo
 mkdir -p "$REPO_ROOT/.claude/skills"
diff --git a/bin/gstack-browser-ensure b/bin/gstack-browser-ensure
index bda9718f5..90037fd6d 100755
--- a/bin/gstack-browser-ensure
+++ b/bin/gstack-browser-ensure
@@ -73,7 +73,7 @@ if [ ! -d "$ROOT/node_modules/playwright" ]; then
   [ "$CHECK" -eq 1 ] && fail "playwright is not installed under $ROOT/node_modules" "cd $ROOT && ./setup"
   command -v bun >/dev/null 2>&1 || fail "playwright is not installed under $ROOT/node_modules and bun is not on PATH" "install Bun, then cd $ROOT && ./setup"
   log "gstack-browser-ensure: installing node modules (bun install)..."
-  (cd "$ROOT" && { bun install --frozen-lockfile >/dev/null 2>&1 || bun install >/dev/null; }) || fail "bun install failed under $ROOT" "cd $ROOT && bun install, then re-run $0"
+  (cd "$ROOT" && { bun install --production --frozen-lockfile >/dev/null 2>&1 || bun install --production >/dev/null; }) || fail "bun install failed under $ROOT" "cd $ROOT && bun install, then re-run $0"
 fi
 
 probe
diff --git a/bun.lock b/bun.lock
index 1ae228532..dc2f348d0 100644
--- a/bun.lock
+++ b/bun.lock
@@ -5,6 +5,7 @@
     "": {
       "name": "gstack",
       "dependencies": {
+        "@anthropic-ai/sdk": "^0.78.0",
         "@huggingface/transformers": "^4.3.1",
         "@ngrok/ngrok": "^1.7.0",
         "cross-spawn": "^7.0.6",
@@ -15,15 +16,14 @@
         "playwright": "^1.62.1",
         "sharp": "^0.35.4",
         "socks": "^2.8.10",
+        "xterm": "^5.3.0",
+        "xterm-addon-fit": "^0.8.0",
       },
       "devDependencies": {
         "@anthropic-ai/claude-agent-sdk": "0.2.141",
-        "@anthropic-ai/sdk": "^0.78.0",
         "@types/bun": "1.4.3",
         "prettier": "3.9.10",
         "typescript": "7.0.2",
-        "xterm": "^5.3.0",
-        "xterm-addon-fit": "^0.8.0",
       },
     },
   },
diff --git a/package.json b/package.json
index 0b396bbf1..214a8209f 100644
--- a/package.json
+++ b/package.json
@@ -69,6 +69,7 @@
     "eval:bg:release": "bun run scripts/eval-bg.ts release"
   },
   "dependencies": {
+    "@anthropic-ai/sdk": "^0.78.0",
     "@huggingface/transformers": "^4.3.1",
     "@ngrok/ngrok": "^1.7.0",
     "cross-spawn": "^7.0.6",
@@ -78,7 +79,9 @@
     "marked": "^18.1.1",
     "playwright": "^1.62.1",
     "sharp": "^0.35.4",
-    "socks": "^2.8.10"
+    "socks": "^2.8.10",
+    "xterm": "^5.3.0",
+    "xterm-addon-fit": "^0.8.0"
   },
   "engines": {
     "bun": ">=1.4.2"
@@ -95,12 +98,9 @@
   ],
   "devDependencies": {
     "@anthropic-ai/claude-agent-sdk": "0.2.141",
-    "@anthropic-ai/sdk": "^0.78.0",
     "@types/bun": "1.4.3",
     "prettier": "3.9.10",
-    "typescript": "7.0.2",
-    "xterm": "^5.3.0",
-    "xterm-addon-fit": "^0.8.0"
+    "typescript": "7.0.2"
   },
   "overrides": {
     "@modelcontextprotocol/sdk": "1.31.0",
diff --git a/setup b/setup
index 10c0ae56c..db0244fee 100755
--- a/setup
+++ b/setup
@@ -1711,6 +1711,15 @@ bun_cmd() {
   "$BUN_CMD" "$@"
 }
 
+# Users get production dependencies only. devDependencies are the test and eval
+# toolchain (the Claude Agent SDK's native binaries alone are ~440 MB on Linux), and
+# nothing setup, the build or an installed skill runs needs them. Bun never
+# prunes packages that are already installed, so a contributor's full
+# `bun install` (CONTRIBUTING.md, bin/dev-setup, CI) survives a later ./setup.
+install_runtime_deps() {
+  bun_cmd install --production --frozen-lockfile 2>/dev/null || bun_cmd install --production
+}
+
 cleanup_copied_bun() {
   local rc=$?
   if [ "${BUN_CMD_WAS_COPIED:-0}" -eq 1 ]; then
@@ -1928,7 +1937,7 @@ if [ "$NEEDS_BUILD" -eq 1 ]; then
   log "Building browse binary..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     if [ "$CSO_BUILD_AVAILABLE" -eq 0 ]; then
       export GSTACK_SETUP_SKIP_CSO_BUILD=1
     fi
@@ -2079,7 +2088,7 @@ if [ "$NEEDS_AGENTS_GEN" -eq 1 ]; then
   log "Generating .agents/ skill docs..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     bun_cmd run gen:skill-docs --host codex --model "$CODEX_GENERATION_MODEL" ${_DISABLED_CSV:+"--disabled-skills=$_DISABLED_CSV"} ${_PLAN_MODE_ARG:+"$_PLAN_MODE_ARG"}
   )
   _prune_stale_generated "$SOURCE_GSTACK_DIR" "$AGENTS_DIR" "$CODEX_SKILLS"
@@ -2092,7 +2101,7 @@ if [ "$INSTALL_FACTORY" -eq 1 ] && { [ "$NEEDS_BUILD" -eq 0 ] || [ -n "$_PLAN_MO
   log "Generating .factory/ skill docs..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     bun_cmd run gen:skill-docs --host factory ${_DISABLED_CSV:+"--disabled-skills=$_DISABLED_CSV"} ${_PLAN_MODE_ARG:+"$_PLAN_MODE_ARG"}
   )
 fi
@@ -2102,7 +2111,7 @@ if [ "$INSTALL_OPENCODE" -eq 1 ] && { [ "$NEEDS_BUILD" -eq 0 ] || [ -n "$_PLAN_M
   log "Generating .opencode/ skill docs..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     bun_cmd run gen:skill-docs --host opencode ${_DISABLED_CSV:+"--disabled-skills=$_DISABLED_CSV"} ${_PLAN_MODE_ARG:+"$_PLAN_MODE_ARG"}
   )
 fi
@@ -2112,7 +2121,7 @@ if [ "$INSTALL_CURSOR" -eq 1 ] && { [ "$NEEDS_BUILD" -eq 0 ] || [ -n "$_PLAN_MOD
   log "Generating .cursor/ skill docs..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     bun_cmd run gen:skill-docs --host cursor ${_DISABLED_CSV:+"--disabled-skills=$_DISABLED_CSV"} ${_PLAN_MODE_ARG:+"$_PLAN_MODE_ARG"}
   )
 fi
@@ -2122,7 +2131,7 @@ if [ "$INSTALL_COPILOT" -eq 1 ] && { [ "$NEEDS_BUILD" -eq 0 ] || [ -n "$_PLAN_MO
   log "Generating .copilot/ skill docs..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     bun_cmd run gen:skill-docs --host copilot ${_DISABLED_CSV:+"--disabled-skills=$_DISABLED_CSV"} ${_PLAN_MODE_ARG:+"$_PLAN_MODE_ARG"}
   )
 fi
@@ -2132,7 +2141,7 @@ if [ "$INSTALL_AGY" -eq 1 ] && { [ "$NEEDS_BUILD" -eq 0 ] || [ -n "$_PLAN_MODE_A
   log "Generating .agy/ skill docs..."
   (
     cd "$SOURCE_GSTACK_DIR"
-    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install
+    install_runtime_deps
     bun_cmd run gen:skill-docs --host agy ${_DISABLED_CSV:+"--disabled-skills=$_DISABLED_CSV"} ${_PLAN_MODE_ARG:+"$_PLAN_MODE_ARG"}
   )
 fi
diff --git a/test/helpers/claude-overlay-fixture.ts b/test/helpers/claude-overlay-fixture.ts
index 17a3c32a0..ded474ef6 100644
--- a/test/helpers/claude-overlay-fixture.ts
+++ b/test/helpers/claude-overlay-fixture.ts
@@ -21,7 +21,7 @@ export const MARKER = 'Effort-match the step';
 export function failableBun(f: Fixture) {
   put(join(f.commands, 'bun'), `#!/usr/bin/env bash
 case "$*" in
-  'install --frozen-lockfile') exit 0 ;;
+  'install --production --frozen-lockfile') exit 0 ;;
   'run build') echo 'Unexpected build in an install fixture' >&2; exit 90 ;;
   *gen:skill-docs*--out-dir*) if [ -f "$HOME/fail-render" ]; then echo 'render failed (fixture)' >&2; exit 7; fi ;;
 esac
diff --git a/test/helpers/install-fixture.ts b/test/helpers/install-fixture.ts
index 7d25bee85..2c08c54b5 100644
--- a/test/helpers/install-fixture.ts
+++ b/test/helpers/install-fixture.ts
@@ -172,7 +172,7 @@ export function makeFixture(): Fixture {
   mkdirSync(home, { recursive: true });
   put(join(commands, 'bun'), `#!/usr/bin/env bash
 case "$*" in
-  'install --frozen-lockfile') exit 0 ;;
+  'install --production --frozen-lockfile') exit 0 ;;
   'run build') echo 'Unexpected build in an install fixture' >&2; exit 90 ;;
   *) exec ${quote(process.execPath)} "$@" ;;
 esac
@@ -248,7 +248,7 @@ export function fixture(layout: string) {
   };
   write(join(commands, 'bun'), `#!/usr/bin/env bash
 case "$*" in
-  'install --frozen-lockfile') exit 0 ;;
+  'install --production --frozen-lockfile') exit 0 ;;
   'build --help') echo 'Fixture Bun has no CSO compile flags'; exit 0 ;;
   'run build') echo 'Unexpected build in registration fixture' >&2; exit 90 ;;
   *) exec ${quote(process.execPath)} "$@" ;;
diff --git a/test/setup-production-deps.test.ts b/test/setup-production-deps.test.ts
new file mode 100644
index 000000000..cdcfdac31
--- /dev/null
+++ b/test/setup-production-deps.test.ts
@@ -0,0 +1,171 @@
+import { afterEach, describe, expect, test } from 'bun:test';
+import { spawnSync } from 'child_process';
+import { builtinModules } from 'module';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { runBashScript } from './helpers/bash-script';
+
+// ./setup installs production dependencies only (GSTA-97). devDependencies are
+// the test and eval toolchain, chiefly the Claude Agent SDK's per-platform
+// native binaries (~440 MB on Linux). This file pins the two halves of that:
+// every install setup runs passes --production (contributors and CI install
+// the full set themselves), and nothing setup, the build or an installed skill
+// loads is a devDependency.
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const read = (rel: string) => fs.readFileSync(path.join(ROOT, rel), 'utf-8');
+const PKG = JSON.parse(read('package.json'));
+const bases: string[] = [];
+afterEach(() => { for (const b of bases.splice(0)) fs.rmSync(b, { recursive: true, force: true }); });
+
+function tempBase(): string {
+  const base = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-prod-deps-'));
+  bases.push(base);
+  return base;
+}
+
+/** A bash function sliced out of a script, by its `name() {` line through the closing `}`. */
+function sliceFunction(source: string, name: string): string {
+  const start = source.indexOf(`\n${name}() {\n`);
+  if (start === -1) throw new Error(`${name}() not found`);
+  const end = source.indexOf('\n}\n', start);
+  return source.slice(start + 1, end + 3);
+}
+
+/** A bun that records each argv line; `install` with --frozen-lockfile exits $FROZEN_RC. */
+function stubBun(base: string): { bun: string; calls: () => string[] } {
+  const log = path.join(base, 'calls');
+  const bun = path.join(base, 'bun');
+  fs.writeFileSync(bun, `#!/usr/bin/env bash\necho "$*" >> ${JSON.stringify(log)}\ncase "$*" in *--frozen-lockfile*) exit "\${FROZEN_RC:-0}" ;; esac\nexit 0\n`, { mode: 0o755 });
+  return { bun, calls: () => (fs.existsSync(log) ? fs.readFileSync(log, 'utf-8').trim().split('\n') : []) };
+}
+
+describe.skipIf(process.platform === 'win32')('setup installs production dependencies only', () => {
+  const setup = read('setup');
+  const script = (bun: string, call: string) =>
+    `set -e\nBUN_CMD=${JSON.stringify(bun)}\n${sliceFunction(setup, 'bun_cmd')}\n${sliceFunction(setup, 'install_runtime_deps')}\n${call}\n`;
+
+  test('install_runtime_deps passes --production with the frozen lockfile, and keeps it on the fallback', () => {
+    const base = tempBase();
+    const { bun, calls } = stubBun(base);
+    expect(runBashScript(script(bun, 'install_runtime_deps'), { env: { ...process.env, FROZEN_RC: '0' } }).status).toBe(0);
+    expect(calls()).toEqual(['install --production --frozen-lockfile']);
+
+    const base2 = tempBase();
+    const stub2 = stubBun(base2);
+    expect(runBashScript(script(stub2.bun, 'install_runtime_deps'), { env: { ...process.env, FROZEN_RC: '1' } }).status).toBe(0);
+    expect(stub2.calls()).toEqual(['install --production --frozen-lockfile', 'install --production']);
+  });
+
+  test('every bun install in setup goes through install_runtime_deps', () => {
+    const body = setup.replace(sliceFunction(setup, 'install_runtime_deps'), '');
+    const direct = body.split('\n').filter((l) => /\b(bun_cmd|"\$BUN_CMD"|bun)\s+install\b/.test(l) && !l.trim().startsWith('#'));
+    expect(direct).toEqual([]);
+    // The build, the Codex render and each host render install first.
+    expect(setup.match(/^\s+install_runtime_deps$/gm)?.length).toBeGreaterThanOrEqual(7);
+    // Negative control: the pre-GSTA-97 line is caught by the same filter.
+    expect(/\b(bun_cmd|"\$BUN_CMD"|bun)\s+install\b/.test('    bun_cmd install --frozen-lockfile 2>/dev/null || bun_cmd install')).toBe(true);
+  });
+
+  test('gstack-browser-ensure installs production dependencies too', () => {
+    const line = read('bin/gstack-browser-ensure').split('\n').find((l) => /bun install/.test(l) && !l.trim().startsWith('#') && !/log /.test(l))!;
+    expect(line).toContain('bun install --production --frozen-lockfile');
+    expect(line).toContain('|| bun install --production >/dev/null');
+  });
+
+  test('bin/dev-setup installs the full set even over a production-only node_modules', () => {
+    const devSetup = read('bin/dev-setup');
+    const start = devSetup.indexOf('# 2. Install dependencies');
+    const block = devSetup.slice(start, devSetup.indexOf('# 3.', start));
+    const base = tempBase();
+    const { bun, calls } = stubBun(base);
+    fs.mkdirSync(path.join(base, 'node_modules'));
+    const r = runBashScript(`set -e\nREPO_ROOT=${JSON.stringify(base)}\nbun() { ${JSON.stringify(bun)} "$@"; }\n${block}`);
+    expect(r.status).toBe(0);
+    expect(calls()).toEqual(['install']);
+  });
+});
+
+/** Bare package names a source file loads (import/require/dynamic import), type-only imports excluded. */
+export function importedPackages(text: string): string[] {
+  const out = new Set<string>();
+  const patterns = [
+    /^\s*import\s+(?!type\b)[^'"\n]*?from\s+['"]([^'"]+)['"]/gm,
+    /^\s*import\s+['"]([^'"]+)['"]/gm,
+    /\brequire\(\s*['"]([^'"]+)['"]\s*\)/g,
+    /\bimport\(\s*['"]([^'"]+)['"]\s*\)/g,
+  ];
+  for (const re of patterns) {
+    for (const m of text.matchAll(re)) {
+      const spec = m[1];
+      if (spec.startsWith('.') || spec.startsWith('/') || spec.startsWith('node:') || spec === 'bun' || spec.startsWith('bun:')) continue;
+      const name = spec.startsWith('@') ? spec.split('/').slice(0, 2).join('/') : spec.split('/')[0];
+      if (builtinModules.includes(name)) continue;
+      out.add(name);
+    }
+  }
+  return [...out];
+}
+
+/** Every shipped-runtime file that loads a package which is not a production dependency. */
+export function nonProductionImports(pkg: { dependencies?: Record<string, string> }, files: Record<string, string>): string[] {
+  const deps = pkg.dependencies ?? {};
+  const bad: string[] = [];
+  for (const [file, text] of Object.entries(files)) {
+    for (const name of importedPackages(text)) if (!(name in deps)) bad.push(`${file}: ${name}`);
+  }
+  return bad.sort();
+}
+
+/** The code setup, the build and installed skills run: shipped dirs plus the scripts setup and the build call by path. */
+function runtimeFiles(): Record<string, string> {
+  const roots = ['bin/', 'lib/', 'browse/src/', 'design/src/', 'make-pdf/src/', 'hosts/', 'extension/', 'scripts/resolvers/'];
+  const tracked = spawnSync('git', ['ls-files'], { cwd: ROOT, encoding: 'utf-8', timeout: 30_000 }).stdout
+    .split('\n').filter((rel) => roots.some((r) => rel.startsWith(r)));
+  const ownPackage = (rel: string) => rel.startsWith('lib/diagram-render/');
+  const invoked = new Set(['scripts/gen-skill-docs.ts']);
+  for (const src of ['setup', 'scripts/build.sh']) for (const m of read(src).matchAll(/scripts\/[A-Za-z0-9_./-]+\.ts/g)) invoked.add(m[0]);
+  const files: Record<string, string> = {};
+  for (const rel of [...tracked, ...invoked]) {
+    if (ownPackage(rel) || /(^|\/)(test|node_modules|dist)\//.test(rel) || /\.(test\.ts|md|json|png|svg|css|html|c|h)$/.test(rel)) continue;
+    const abs = path.join(ROOT, rel);
+    if (!fs.existsSync(abs) || !fs.statSync(abs).isFile() || fs.statSync(abs).size > 2_000_000) continue;
+    const text = fs.readFileSync(abs, 'utf-8');
+    if (text.includes('\u0000')) continue;
+    files[rel] = text;
+  }
+  return files;
+}
+
+describe('setup and runtime need only production dependencies', () => {
+  test('no shipped code loads a devDependency or an undeclared package', () => {
+    const files = runtimeFiles();
+    expect(Object.keys(files).length).toBeGreaterThan(300);
+    expect(nonProductionImports(PKG, files)).toEqual([]);
+  });
+
+  test('negative controls: a devDependency import and a moved-back runtime package are caught', () => {
+    expect(nonProductionImports(PKG, { 'bin/x': "import { query } from '@anthropic-ai/claude-agent-sdk';" })).toEqual(['bin/x: @anthropic-ai/claude-agent-sdk']);
+    expect(nonProductionImports(PKG, { 'bin/x': "import type { Q } from '@anthropic-ai/claude-agent-sdk';\nimport fs from 'node:fs';" })).toEqual([]);
+    const { ['@anthropic-ai/sdk']: _sdk, ...rest } = PKG.dependencies;
+    const files = runtimeFiles();
+    expect(nonProductionImports({ dependencies: rest }, files)).toContain('bin/gstack-distill-free-text: @anthropic-ai/sdk');
+  });
+
+  test('packages the build copies out of node_modules are production dependencies', () => {
+    const scripts: Record<string, string> = PKG.scripts;
+    const run = [...read('scripts/build.sh').matchAll(/"\$BUN_CMD" run ([A-Za-z0-9:_-]+)/g)].map((m) => m[1]);
+    expect(run).toContain('vendor:xterm');
+    const copied = run.flatMap((name) => [...(scripts[name] ?? '').matchAll(/node_modules\/((?:@[^/\s]+\/)?[^/\s]+)\//g)].map((m) => m[1]));
+    expect(copied.sort()).toEqual(['xterm', 'xterm', 'xterm-addon-fit']);
+    for (const name of copied) expect(PKG.dependencies).toHaveProperty([name]);
+  });
+
+  test('the dev toolchain stays out of the user install', () => {
+    for (const name of ['@anthropic-ai/claude-agent-sdk', 'typescript', 'prettier', '@types/bun']) {
+      expect(PKG.devDependencies).toHaveProperty([name]);
+      expect(PKG.dependencies).not.toHaveProperty([name]);
+    }
+  });
+});
diff --git a/test/team-mode.test.ts b/test/team-mode.test.ts
index efd4ff0f0..ad36946a2 100644
--- a/test/team-mode.test.ts
+++ b/test/team-mode.test.ts
@@ -485,7 +485,7 @@ describe('setup --team / --no-team / -q', () => {
       fs.writeFileSync(path.join(commands, 'bun'), `#!/usr/bin/env bash
 [ "$1 $2" = '--no-env-file --config=/dev/null' ] && shift 2
 case "$*" in
-  'install --frozen-lockfile') exit 0 ;;
+  'install --production --frozen-lockfile') exit 0 ;;
   'build --help') echo 'Fixture Bun has no CSO compile flags'; exit 0 ;;
   *'/bin/gstack-migrate-claude-code --install-dir '*)
     [[ "$#" -eq 5 && "$2" = --install-dir && "$4" = --skills-dir ]] || exit 90