test+fix(memory-ingest): strengthen regression tests, fix inject for malformed-close frontmatter

Imports the shim-based regression tests from PR #1341 (Alex Medina) and
strengthens them to assert title, type, and tags actually arrive in put
stdin — not just `agent: claude-code`. Asserting the metadata fields
matches the regression class that's caused this fix wave: writers can
"succeed" while metadata is silently lost. The original PR #1341 tests
would have passed even with title/type/tags missing.

Strengthening the test surfaced a deeper issue. buildTranscriptPage joins
frontmatter array elements with "\n" and does not append a trailing
newline, so the close fence is "\n---<content>" directly, not "\n---\n".
PR #1328's inject branch searched for "\n---\n" and never matched —
which means even with PR #1328 alone, transcript pages were landing in
gbrain with no title/type/tags. Two-line fix: search for "\n---" only,
since the inject lands before the close fence regardless of what
follows it.

Also imports PR #1341's V1.5 NOTE doc-block update and the section
comment refresh so the prose stays accurate against the new writer
shape.

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

bin/gstack-memory-ingest.ts

@@ -786,7 +786,12 @@ function gbrainPutPage(page: PageRecord): { ok: boolean; error?: string } {
   //    land in gbrain with empty title/type/tags.
   let body = page.body;
   if (body.startsWith("---\n")) {
-    const end = body.indexOf("\n---\n", 4);
+    // Locate the closing --- delimiter. buildTranscriptPage joins with "\n"
+    // and does not append a trailing newline, so the close fence looks like
+    // "...\n---" followed directly by body content (no "\n---\n" pattern).
+    // Match the close on "\n---" only — the inject lands BEFORE the close
+    // fence, inside the frontmatter block, regardless of what follows it.
+    const end = body.indexOf("\n---", 4);
     if (end > 0) {
       const inject = [
         `title: ${JSON.stringify(page.title)}`,