fix(cli): set `npm_config_user_agent` when running npm packages or tasks (#26639)

Fixes #25342.

Still not sure on the exact user agent to set (should it include
`node`?).

After this PR, here's the state of running some `create-*` packages
(just ones I could think of off the top of my head):

| package                  | prints/runs/suggests deno install | notes |
| ---------------- | ------------- | ------ |
| `create-next-app` | ❌ | falls back to npm, needs a PR
([code](https://github.com/vercel/next.js/blob/c32e2802097c03fd9f95b1dae228d6e0257569c0/packages/create-next-app/helpers/get-pkg-manager.ts#L3))
| `sv create` | ❌ | uses `package-manager-detector`, needs a PR
([code](https://github.com/antfu-collective/package-manager-detector/tree/main))
| `create-qwik` | ✅ | runs `deno install` but suggests `deno start`
which doesn't work (should be `deno task start` or `deno run start`)
| `create-astro` | ✅ | runs `deno install` but suggests `npm run dev`
later in output, probably needs a PR
| `nuxi init` | ❌ | deno not an option in dialog, needs a PR
([code](https://github.com/nuxt/cli/blob/f04e2e894446f597da9d971b7eb03191d5a0da7e/src/commands/init.ts#L96-L102))
| `create-react-app` | ❌ | uses npm
| `ng new` (`@angular/cli`) | ❌ | uses npm
| `create-vite` | ✅ | suggests working deno commands 🎉 
| `create-solid` |  ❌ | suggests npm commands, needs PR

It's possible that fixing `package-manager-detector` or other packages
might make some of these just work, but haven't looked too carefully at
each

8 files changed, 72 insertions, 0 deletions

diff --git a/tests/specs/npm/user_agent_env_var/__test__.jsonc b/tests/specs/npm/user_agent_env_var/__test__.jsonc
new file mode 100644
index 000000000..a2af970a0
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/__test__.jsonc
@@ -0,0 +1,46 @@
+{
+  "tempDir": true,
+  "tests": {
+    "set_for_npm_package": {
+      "steps": [
+        {
+          "args": "install",
+          "output": "[WILDCARD]"
+        },
+        {
+          "args": "run -A npm:@denotest/print-npm-user-agent",
+          "output": "run.out"
+        }
+      ]
+    },
+    "unset_for_local_file": {
+      "steps": [
+        {
+          "args": "run -A main.ts",
+          "output": "Download [WILDCARD]\nnpm_config_user_agent: undefined\n"
+        }
+      ]
+    },
+    "set_for_tasks": {
+      "steps": [
+        {
+          "args": "install",
+          "output": "[WILDCARD]"
+        },
+        {
+          "args": "task run-via-bin",
+          "output": "bin_command.out"
+        }
+      ]
+    },
+    "set_for_lifecycle_scripts": {
+      "steps": [
+        {
+          "args": "install --allow-scripts",
+          "output": "postinstall.out",
+          "exitCode": 1
+        }
+      ]
+    }
+  }
+}
diff --git a/tests/specs/npm/user_agent_env_var/bin_command.out b/tests/specs/npm/user_agent_env_var/bin_command.out
new file mode 100644
index 000000000..c8e941303
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/bin_command.out
@@ -0,0 +1,2 @@
+Task run-via-bin print-npm-user-agent
+npm_config_user_agent: deno/[WILDCARD] npm/? deno/[WILDCARD] [WILDCARD] [WILDCARD]
diff --git a/tests/specs/npm/user_agent_env_var/deno.jsonc b/tests/specs/npm/user_agent_env_var/deno.jsonc
new file mode 100644
index 000000000..fbd70ec48
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/deno.jsonc
@@ -0,0 +1,3 @@
+{
+  "nodeModulesDir": "auto"
+}
diff --git a/tests/specs/npm/user_agent_env_var/main.ts b/tests/specs/npm/user_agent_env_var/main.ts
new file mode 100644
index 000000000..2c51107e3
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/main.ts
@@ -0,0 +1 @@
+console.log(`npm_config_user_agent: ${Deno.env.get("npm_config_user_agent")}`);
diff --git a/tests/specs/npm/user_agent_env_var/package.json b/tests/specs/npm/user_agent_env_var/package.json
new file mode 100644
index 000000000..12cc0cc6f
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/package.json
@@ -0,0 +1,8 @@
+{
+  "scripts": {
+    "run-via-bin": "print-npm-user-agent"
+  },
+  "dependencies": {
+    "@denotest/print-npm-user-agent": "1.0.0"
+  }
+}
diff --git a/tests/specs/npm/user_agent_env_var/postinstall.out b/tests/specs/npm/user_agent_env_var/postinstall.out
new file mode 100644
index 000000000..19a08598f
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/postinstall.out
@@ -0,0 +1,10 @@
+Download http://localhost:4260/@denotest%2fprint-npm-user-agent
+Download http://localhost:4260/@denotest/print-npm-user-agent/1.0.0.tgz
+Initialize @denotest/print-npm-user-agent@1.0.0
+Initialize @denotest/print-npm-user-agent@1.0.0: running 'postinstall' script
+error: script 'postinstall' in '@denotest/print-npm-user-agent@1.0.0' failed with exit code 1
+stdout:
+postinstall
+npm_config_user_agent: deno/[WILDCARD] npm/? deno/[WILDCARD] [WILDCARD] [WILDCARD]
+
+error: failed to run scripts for packages: @denotest/print-npm-user-agent@1.0.0
diff --git a/tests/specs/npm/user_agent_env_var/run.out b/tests/specs/npm/user_agent_env_var/run.out
new file mode 100644
index 000000000..a630ac412
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/run.out
@@ -0,0 +1 @@
+npm_config_user_agent: deno/[WILDCARD] npm/? deno/[WILDCARD] [WILDCARD] [WILDCARD]
diff --git a/tests/specs/npm/user_agent_env_var/test.mjs b/tests/specs/npm/user_agent_env_var/test.mjs
new file mode 100644
index 000000000..ae035d40e
--- /dev/null
+++ b/tests/specs/npm/user_agent_env_var/test.mjs
@@ -0,0 +1 @@
+console.log(process.env.npm_config_user_agent);