fix(cookbook): stop Ollama runner from executing the install one-liner (#3926)

The generated bash runner printed the missing-ollama hint with the install
one-liner wrapped in backticks inside a double-quoted echo. Backticks in
double quotes are command substitution, so on any serve target without
ollama the script downloaded and ran the system-wide installer (including
remote SSH hosts) instead of printing the hint. _validate_serve_cmd rejects
backticks in user-supplied commands for exactly this reason; the app's own
generated script never goes through that validator.

Move the hint into OLLAMA_MISSING_HINT in cookbook_helpers (no substitution
tokens) and emit it single-quoted via _bash_squote. Tests assert the hint
has no expansion tokens, that no generated echo line carries backticks
inside double quotes, and that bash prints the line literally.

Fixes #3816

routes/cookbook_helpers.py

@@ -558,6 +558,18 @@ def _bash_squote(v: str) -> str:
     return v.replace("'", "'\\''")
 
 
+# Shown by generated runner scripts when the ollama binary is missing on the
+# target host. Must stay free of backticks/$( ) and be emitted single-quoted:
+# an earlier version wrapped the install one-liner in backticks inside a
+# double-quoted echo, which bash executed as command substitution and ran the
+# system-wide installer (including on remote SSH hosts) instead of printing
+# the hint.
+OLLAMA_MISSING_HINT = (
+    "ERROR: Ollama not found on this server. Install it from "
+    "https://ollama.com/download or run: curl -fsSL https://ollama.com/install.sh | sh"
+)
+
+
 # Allow-list of binaries permitted as the leading token of `req.cmd` for /api/model/serve.
 # Anything else is rejected before the cmd is interpolated into a tmux/PowerShell wrapper.
 _SERVE_CMD_ALLOWLIST = {

routes/cookbook_routes.py

@@ -49,7 +49,7 @@ logger = logging.getLogger(__name__)
 from routes.cookbook_helpers import (
     _SESSION_ID_RE, _validate_repo_id, _validate_serve_model_id, _validate_include, _validate_token,
     _validate_local_dir, _validate_gpus, _shell_path,
-    _ps_squote, _bash_squote, _validate_serve_cmd, _parse_serve_phase,
+    _ps_squote, _bash_squote, _validate_serve_cmd, _parse_serve_phase, OLLAMA_MISSING_HINT,
     _safe_env_prefix, _local_tooling_path_export, _append_serve_preflight_exit_lines,
     _append_serve_exit_code_lines, _append_llama_cpp_linux_accel_build_lines, _cached_model_scan_script,
     load_stored_hf_token,
@@ -1861,7 +1861,10 @@ def setup_cookbook_routes() -> APIRouter:
                 runner_lines.append('  exec 3<&-; exec 3>&-')
                 runner_lines.append('done')
                 runner_lines.append('if ! command -v ollama &>/dev/null; then')
-                runner_lines.append('  echo "ERROR: Ollama not found on this server. Install it from https://ollama.com/download or `curl -fsSL https://ollama.com/install.sh | sh`."')
+                # Single-quoted on purpose: backticks inside a double-quoted
+                # echo are command substitution, and this line used to run the
+                # curl|sh installer on the target host instead of printing it.
+                runner_lines.append(f"  echo '{_bash_squote(OLLAMA_MISSING_HINT)}'")
                 runner_lines.append('  echo')
                 runner_lines.append('  echo "=== Process exited with code 127 ==="')
                 runner_lines.append('  exec bash -i')

tests/test_ollama_runner_hint.py

@@ -0,0 +1,57 @@
+"""The generated Ollama runner must print the install hint, not execute it.
+
+The runner script emitted by /api/model/serve contained:
+
+    echo "ERROR: Ollama not found ... or `curl -fsSL .../install.sh | sh`."
+
+Backticks inside double quotes are bash command substitution, so on any host
+without ollama the script downloaded and ran the system-wide installer
+(including remote SSH serve targets) instead of printing the hint. The hint
+now lives in OLLAMA_MISSING_HINT, contains no substitution tokens, and is
+emitted single-quoted.
+"""
+import os
+import shutil
+import subprocess
+
+import pytest
+
+from routes.cookbook_helpers import OLLAMA_MISSING_HINT, _bash_squote
+
+ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
+
+def test_hint_has_no_shell_expansion_tokens():
+    assert "`" not in OLLAMA_MISSING_HINT
+    assert "$(" not in OLLAMA_MISSING_HINT
+
+
+def test_hint_still_tells_the_user_how_to_install():
+    assert "https://ollama.com/download" in OLLAMA_MISSING_HINT
+    assert "install.sh" in OLLAMA_MISSING_HINT
+
+
+def test_no_runner_echo_line_uses_backticks_in_double_quotes():
+    # Source-level guard: generated-script echo lines must never carry
+    # backticks inside a double-quoted bash string again.
+    src = open(os.path.join(ROOT, "routes", "cookbook_routes.py"), encoding="utf-8").read()
+    offenders = [
+        line.strip()
+        for line in src.splitlines()
+        if "append(" in line and 'echo "' in line and "`" in line.split('echo "', 1)[1]
+    ]
+    assert offenders == []
+
+
+def test_single_quoted_echo_prints_hint_literally():
+    bash = shutil.which("bash")
+    if not bash:
+        pytest.skip("bash not available")
+    out = subprocess.run(
+        [bash, "-c", f"echo '{_bash_squote(OLLAMA_MISSING_HINT)}'"],
+        capture_output=True,
+        text=True,
+        timeout=30,
+    )
+    assert out.returncode == 0
+    assert out.stdout.strip() == OLLAMA_MISSING_HINT