p0 line landing: coord board/roll + wrapper usage contract + dispatch layer (successor to #1467) (#1468)

Co-authored-by: orch-01 <[email protected]>

packages/mosaic/src/commands/brain-dispatch.ts

@@ -0,0 +1,67 @@
+import { spawnSync } from 'node:child_process';
+import { accessSync, constants } from 'node:fs';
+import { join } from 'node:path';
+
+import { resolveBrainHome } from '../fleet/brain-home.js';
+
+/**
+ * Shared brain-tool dispatch (fleet CLI integration, Jason ruling
+ * 2026-08-28): the npm package embeds the COMMAND SURFACE; operator-owned
+ * implementations stay in the brain (tools/). Commands resolve the brain
+ * home (MOSAIC_BRAIN_HOME wins — see brain-home.ts) and exec the tool
+ * there. Nothing operator-specific ships inside the package.
+ *
+ * Pass-through contract: arguments, stdout/stderr, and the exit code belong
+ * to the tool. The CLI adds nothing on success; absent tools fail loudly
+ * with the resolved path (127) instead of guessing.
+ */
+
+/** Absolute path of a brain-relative tool. */
+export function resolveBrainTool(mosaicHome: string, relPath: string): string {
+  return join(resolveBrainHome(mosaicHome), ...relPath.split('/'));
+}
+
+/** Map a spawnSync result + tool existence to the CLI exit status. */
+export function exitStatusFor(
+  result: { status: number | null; error?: NodeJS.ErrnoException },
+  toolExists: boolean,
+): number {
+  if (!toolExists) return 127;
+  if (result.status !== null) return result.status;
+  return 125; // killed by signal / could not run
+}
+
+export function brainToolExists(tool: string): boolean {
+  try {
+    accessSync(tool, constants.X_OK);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Exec a brain tool with full pass-through. `interpreter` runs the tool
+ * through e.g. python3 (renderers); omit it for executable scripts.
+ * Returns the process exit status; callers assign it to process.exitCode.
+ */
+export function execBrainTool(
+  mosaicHome: string,
+  relPath: string,
+  args: string[],
+  interpreter?: string,
+): number {
+  const tool = resolveBrainTool(mosaicHome, relPath);
+  if (!brainToolExists(tool)) {
+    console.error(
+      `mosaic: brain tool not found (expected ${tool}). ` +
+        'Tool suites live in the brain tree under tools/; ' +
+        'check MOSAIC_BRAIN_HOME or the brain checkout.',
+    );
+    return 127;
+  }
+  const result = interpreter
+    ? spawnSync(interpreter, [tool, ...args], { stdio: 'inherit', env: process.env })
+    : spawnSync(tool, args, { stdio: 'inherit', env: process.env });
+  return exitStatusFor(result, true);
+}