fix(ai): resolve engine aliases for ai({ engine })

`ai(prompt, { engine: "cc" })` failed with "ai() needs an installed engine"
even with Claude installed, because pickAiEngine() matched raw ENGINES keys and
never consulted ALIASES — while /agents, start and upgrade all resolve aliases
(README: "name any; alias ok"). Under --dry-run it was worse: the raw alias
reached aiExecArgs() and threw "no headless mode", though a dry run is meant to
narrate without requiring an installed engine.

Resolve the preference through resolveEngine() and let the dry-run fallback do
the same. An unknown name still yields null, and a named-but-not-installed
engine still refuses to fall back to another one.

Author: clawedassistant26

src/cli.mjs

@@ -17,7 +17,7 @@
 // Under --dry-run it narrates the argv instead of spawning.
 import { spawnSync } from "node:child_process";
 import { fileURLToPath } from "node:url";
-import { ENGINES, aiExecArgs, pickAiEngine } from "./engines.mjs";
+import { ENGINES, aiExecArgs, pickAiEngine, resolveEngine } from "./engines.mjs";
 
 // Resolve THIS package's own moshcode entrypoint, so scripting stays
 // self-referential and doesn't depend on `moshcode` being on PATH.
@@ -68,8 +68,10 @@ export function cliVerb(name, summary) {
  */
 export function runAi(ctx, prompt, opts = {}) {
   if (ctx.dryRun) {
-    // narrate without requiring an installed engine
-    const engine = pickAiEngine(opts.engine) || opts.engine || "claude";
+    // narrate without requiring an installed engine — so the fallback has to
+    // resolve an alias itself: with nothing installed pickAiEngine() returns
+    // null, and handing the raw alias to aiExecArgs threw instead of narrating.
+    const engine = pickAiEngine(opts.engine) || resolveEngine(opts.engine)?.[0] || opts.engine || "claude";
     const args = aiExecArgs(engine, prompt); // throws only on an unknown engine name
     ctx.out(`  🧠 ai(${JSON.stringify(String(prompt).slice(0, 48))}) → would run: ${engine} ${args.join(" ")}`);
     return "";

src/engines.mjs

@@ -153,9 +153,19 @@ export function aiExecArgs(engine, prompt) {
   return fn(String(prompt));
 }
 
-/** First installed engine that supports headless ai(), honoring a preference. */
+/**
+ * First installed engine that supports headless ai(), honoring a preference.
+ *
+ * A preference names an engine the same way every other engine surface does
+ * (`/agents cc`, `moshcode start cc`, `moshcode upgrade cc` — README: "name
+ * any; alias ok"), so resolve ALIASES here too. Matching raw ENGINES keys only
+ * made `ai(prompt, { engine: "cc" })` read as "no such engine" and fail with
+ * "needs an installed engine" even when Claude was installed. An unknown name
+ * still yields null.
+ */
 export function pickAiEngine(preferred) {
-  const order = preferred ? [preferred] : ["claude", "codex", "opencode", "gemini", "aider"];
+  const wanted = preferred ? resolveEngine(preferred)?.[0] : null;
+  const order = preferred ? (wanted ? [wanted] : []) : ["claude", "codex", "opencode", "gemini", "aider"];
   for (const key of order) {
     if (Object.hasOwn(ENGINES, key) && Object.hasOwn(AI_EXEC, key) && isInstalled(ENGINES[key].bin)) return key;
   }

test/cli.test.mjs

@@ -147,6 +147,16 @@ test("ai() in dry-run narrates the engine invocation and returns empty string",
   assert.match(ctx.lines.join("\n"), /would run: codex exec/);
 });
 
+test("ai() in dry-run narrates an aliased engine instead of throwing", () => {
+  // A dry run narrates without requiring an installed engine, so with nothing
+  // installed pickAiEngine() returns null and the fallback has to resolve the
+  // alias itself — handing the raw "cc" to aiExecArgs threw "no headless mode".
+  const ctx = { dryRun: true, lines: [], out(l) { this.lines.push(l); } };
+  const out = runAi(ctx, "summarize the diff", { engine: "cc" });
+  assert.equal(out, "");
+  assert.match(ctx.lines.join("\n"), /would run: claude -p/);
+});
+
 // R8: non-zero exits return { ok: false } instead of throwing, so scripts can
 // branch on outcomes without a try/catch.
 test("R8: a non-zero CLI exit returns { ok: false } instead of throwing", async () => {

test/engines.test.mjs

@@ -158,6 +158,25 @@ test("ranOk and exitReason cover clean exits, bad codes, and spawn errors", asyn
   assert.match(exitReason(missing), /ENOENT|not found|spawn/i);
 });
 
+test("pickAiEngine resolves an engine alias, like every other engine surface", () => {
+  // `/agents cc`, `moshcode start cc` and `moshcode upgrade cc` all resolve the
+  // alias, so an ai() preference must too — otherwise `ai(p, { engine: "cc" })`
+  // reports "needs an installed engine" with Claude sitting right there on PATH.
+  const dir = tempDir("moshcode-ai-alias-");
+  writeEngine(dir, "claude");
+  const previous = process.env.PATH;
+  process.env.PATH = `${dir}${path.delimiter}${previous || ""}`;
+  try {
+    assert.equal(pickAiEngine("claude"), "claude");
+    assert.equal(pickAiEngine("cc"), "claude");
+    assert.equal(pickAiEngine("claude-code"), "claude");
+    // an unknown preference is still no engine at all
+    assert.equal(pickAiEngine("definitely-not-an-engine"), null);
+  } finally {
+    process.env.PATH = previous;
+  }
+});
+
 test("engine lookup ignores inherited Object.prototype members", () => {
   // ENGINES/ALIASES/AI_EXEC are plain object literals, so an unknown name that
   // matches an Object.prototype member must not resolve as a real engine.