fix(memory-ingest): hybrid frontmatter writer + tightened gbrain availability probe

PR #1328 (merged in the prior commit) correctly injects title/type/tags
into the YAML frontmatter that buildTranscriptPage already prepends. But
buildArtifactPage emits raw markdown without frontmatter, so design-docs,
learnings, and builder-profile-entries were landing in gbrain with empty
title/type/tags. Add the no-frontmatter wrap branch so artifact pages get
the same metadata the inject branch provides for transcripts.

Also bring in gbrainAvailable()'s --help probe (originally proposed in
PR #1341 by Alex Medina), with the regex tightened from /(^|\s)put(\s|$)/m
to /^\s+put\s/m. Anchoring on the indented subcommand format gbrain's
help actually uses keeps the probe from matching "put" appearing as
prose in help text, while still failing fast with one clean error if a
future gbrain renames or removes the put subcommand.

Updates the V1.5 NOTE doc block at the top of the file to describe the
current put-via-stdin shape rather than the legacy put_page flag form.

Co-Authored-By: Alex Medina <oficina@puntoverdemc.com>

bin/gstack-memory-ingest.ts

@@ -34,8 +34,9 @@
  * keep V1 ship-tight. See TODOS.md.
  *
  * V1.5 NOTE: When `gbrain put_file` ships in the gbrain CLI (cross-repo P0 TODO),
- * transcripts will route to Supabase Storage instead of put_page. Until then, all
- * content rides put_page; gbrain's native dedup keys on session_id.
+ * transcripts will route to Supabase Storage instead of the page-write path.
+ * Until then, all content rides `gbrain put <slug>` (stdin, YAML frontmatter for
+ * title/type/tags); gbrain's native dedup keys on session_id.
  */
 
 import {
@@ -745,14 +746,25 @@ function buildArtifactPage(path: string, type: MemoryType): PageRecord {
   };
 }
 
-// ── Writer (calls gbrain put_page) ─────────────────────────────────────────
+// ── Writer (calls `gbrain put`) ────────────────────────────────────────────
 
 let _gbrainAvailability: boolean | null = null;
 function gbrainAvailable(): boolean {
   if (_gbrainAvailability !== null) return _gbrainAvailability;
   try {
     execSync("command -v gbrain", { stdio: "ignore" });
-    _gbrainAvailability = true;
+    // gbrain v0.27 retired the legacy `put_page` flag-form for `put <slug>`
+    // (content via stdin, metadata as YAML frontmatter). Probe `--help` for
+    // the `put` subcommand so we surface a single clean error here rather
+    // than failing every page with "Unknown command: put_page". The regex
+    // anchors on the indented subcommand format gbrain's help actually uses
+    // ("  put   ..."), not any whitespace-bordered "put" word in prose.
+    const help = execFileSync("gbrain", ["--help"], {
+      encoding: "utf-8",
+      timeout: 5000,
+      stdio: ["ignore", "pipe", "pipe"],
+    });
+    _gbrainAvailability = /^\s+put\s/m.test(help);
   } catch {
     _gbrainAvailability = false;
   }
@@ -761,12 +773,17 @@ function gbrainAvailable(): boolean {
 
 function gbrainPutPage(page: PageRecord): { ok: boolean; error?: string } {
   if (!gbrainAvailable()) {
-    return { ok: false, error: "gbrain CLI not in PATH" };
+    return { ok: false, error: "gbrain CLI not in PATH or missing `put` subcommand" };
   }
-  // gbrain CLI verb is `put <slug>`; it does NOT accept --title / --type /
-  // --tags flags. (`put_page` is the MCP tool name, not the CLI subcommand.)
-  // Inject title/type/tags into the YAML frontmatter that page.body already
-  // begins with so gbrain's frontmatter parser picks them up.
+  // gbrain v0.27+ uses `put <slug>` (positional, content via stdin) instead
+  // of the legacy `put_page` flag form. Metadata rides as YAML frontmatter:
+  //  - When the page body already starts with frontmatter (transcripts), inject
+  //    title/type/tags into the existing block so gbrain's frontmatter parser
+  //    picks them up.
+  //  - When the page body has no frontmatter (raw artifacts: design-docs,
+  //    learnings, builder-profile-entries), wrap with a fresh frontmatter
+  //    carrying the same fields. Without this branch, artifact pages would
+  //    land in gbrain with empty title/type/tags.
   let body = page.body;
   if (body.startsWith("---\n")) {
     const end = body.indexOf("\n---\n", 4);
@@ -779,6 +796,16 @@ function gbrainPutPage(page: PageRecord): { ok: boolean; error?: string } {
       ].join("\n");
       body = body.slice(0, end) + "\n" + inject + body.slice(end);
     }
+  } else {
+    body = [
+      "---",
+      `title: ${JSON.stringify(page.title)}`,
+      `type: ${page.type}`,
+      `tags: [${page.tags.map((t) => JSON.stringify(t)).join(", ")}]`,
+      "---",
+      "",
+      body,
+    ].join("\n");
   }
   try {
     execFileSync("gbrain", ["put", page.slug], {