Point agents at --schema from top-level help (AGI-1169)

CHANGELOG.md

@@ -19,6 +19,10 @@ that may never merge. They are not releases and are not listed here.
 
 ## Unreleased
 
+- When a coding agent runs `mapbox --help` (detected the same way as for
+  the `User-Agent`), the help opens with a two-line hint pointing at
+  `mapbox --schema`. Help for people, and for subcommands, is unchanged.
+
 - **Breaking**: `--eta-type`, `--navigation-profile` and `--origin` removed
   from `mapbox search category`. The category endpoint does not currently
   return an ETA, so the flags were accepted but had no effect. A script

src/main.rs

@@ -53,6 +53,13 @@ use spec::ServiceSpec;
 /// single source for the Rust half rather than for all three.
 const REPO_URL: &str = "https://github.com/mapbox/cli";
 
+/// Opens the top-level help when an agent is driving the CLI. Agents explore
+/// by chaining `--help` calls, one command at a time; `--schema` answers the
+/// same question for every command in one document.
+const AGENT_HELP_HINT: &str = "\
+Agents: `mapbox --schema` describes every command, its arguments and the request it makes
+as one JSON document. Use it instead of chaining --help calls.";
+
 /// Rejects a value the spec says is a number, while still yielding a
 /// `String`.
 ///
@@ -770,7 +777,12 @@ fn cli() -> u8 {
         }
     };
 
-    let app = build_app(&specs);
+    let mut app = build_app(&specs);
+    // Here rather than in `build_app`, which tests call directly and which
+    // should not depend on who happens to be running them.
+    if agent_detect::detect_agent().is_some() {
+        app = app.before_help(AGENT_HELP_HINT);
+    }
     let argv = tilesets_cli::escape_passthrough_args(&app, raw_argv.clone());
     // Parsing consumes the tree, and `--schema` still has to read it
     // afterwards — so the parse gets the copy and `app` stays whole.

tests/output_contract.rs

@@ -363,6 +363,49 @@ fn help_is_never_wrapped() {
     assert!(text.contains("--output"), "--output should be documented");
 }
 
+const AGENT_HINT: &str = "Agents: `mapbox --schema`";
+
+/// An agent reading top-level help is pointed at `--schema` rather than left
+/// to chain `--help` calls. Only there: subcommand help stays as it was.
+#[test]
+fn an_agent_is_pointed_at_the_schema() {
+    let out = command()
+        .env("CLAUDECODE", "1")
+        .arg("--help")
+        .output()
+        .expect("run mapbox");
+    assert!(out.status.success());
+    assert!(stdout(&out).contains(AGENT_HINT), "{}", stdout(&out));
+
+    let sub = command()
+        .env("CLAUDECODE", "1")
+        .args(["styles", "--help"])
+        .output()
+        .expect("run mapbox");
+    assert!(!stdout(&sub).contains(AGENT_HINT), "{}", stdout(&sub));
+}
+
+/// A person gets the help they always did. The environment is cleared rather
+/// than having agent variables removed one by one: the suite itself often
+/// runs under an agent, and `agent_detect` knows more variables than this
+/// file should have to list.
+#[test]
+fn without_an_agent_the_help_has_no_hint() {
+    let home = sandbox_home();
+    let mut cmd = Command::new(env!("CARGO_BIN_EXE_mapbox"));
+    cmd.env_clear()
+        .env("HOME", &home)
+        .env("MAPBOX_CONFIG_DIR", home.join(".mapbox"));
+    // Windows processes expect this one; nothing reads it as an agent.
+    if let Some(root) = std::env::var_os("SystemRoot") {
+        cmd.env("SystemRoot", root);
+    }
+    let out = cmd.arg("--help").output().expect("run mapbox");
+
+    assert!(out.status.success());
+    assert!(!stdout(&out).contains(AGENT_HINT), "{}", stdout(&out));
+}
+
 /// An operation that can never succeed is not in the command surface, so it
 /// answers exactly as a mistyped name does — same code, same shape, same
 /// exit. Anything else would tell a caller which scopes exist while still