Initial import from garrytan/gstack@026751e (main snapshot via local relay)

Source: https://github.com/garrytan/gstack/commit/026751e

scripts/resolvers/model-overlay.ts

@@ -0,0 +1,60 @@
+/**
+ * Model overlay resolver — reads model-overlays/{model}.md and returns it
+ * wrapped in a subordinate behavioral-patch section.
+ *
+ * Precedence:
+ *   1. Exact match: ctx.model === 'gpt-5.4' → reads model-overlays/gpt-5.4.md
+ *   2. INHERIT directive: if the file's first non-whitespace line is
+ *      `{{INHERIT:claude}}`, the resolver reads model-overlays/claude.md first
+ *      and concatenates it ahead of the rest of this file's content.
+ *      This lets `gpt-5.4.md` build on top of `gpt.md` without duplication.
+ *   3. Missing file: returns empty string (graceful degradation, no error).
+ *   4. No ctx.model set: returns empty string.
+ *
+ * The returned block is subordinate to skill workflow, safety gates, and
+ * AskUserQuestion instructions. The subordination language is part of the
+ * wrapper heading so it appears with every overlay regardless of file content.
+ */
+
+import * as fs from 'fs';
+import * as path from 'path';
+import type { TemplateContext } from './types';
+
+const OVERLAY_DIR = path.resolve(import.meta.dir, '../../model-overlays');
+
+const INHERIT_RE = /^\s*\{\{INHERIT:([a-z0-9-]+(?:\.[0-9]+)*)\}\}\s*\n/;
+
+export function readOverlay(model: string, seen: Set<string> = new Set()): string {
+  if (seen.has(model)) return ''; // cycle guard
+  seen.add(model);
+
+  const filePath = path.join(OVERLAY_DIR, `${model}.md`);
+  if (!fs.existsSync(filePath)) return '';
+
+  const raw = fs.readFileSync(filePath, 'utf-8');
+  const match = raw.match(INHERIT_RE);
+  if (!match) return raw.trim();
+
+  const baseModel = match[1];
+  const base = readOverlay(baseModel, seen);
+  const rest = raw.replace(INHERIT_RE, '').trim();
+
+  if (!base) return rest;
+  return `${base}\n\n${rest}`;
+}
+
+export function generateModelOverlay(ctx: TemplateContext): string {
+  if (!ctx.model) return '';
+
+  const content = readOverlay(ctx.model);
+  if (!content) return '';
+
+  return `## Model-Specific Behavioral Patch (${ctx.model})
+
+The following nudges are tuned for the ${ctx.model} model family. They are
+**subordinate** to skill workflow, STOP points, AskUserQuestion gates, plan-mode
+safety, and /ship review gates. If a nudge below conflicts with skill instructions,
+the skill wins. Treat these as preferences, not rules.
+
+${content}`;
+}