diff --git a/bin/gstack-memory-ingest.ts b/bin/gstack-memory-ingest.ts
index 2552dee88d..77177dd010 100644
--- a/bin/gstack-memory-ingest.ts
+++ b/bin/gstack-memory-ingest.ts
@@ -744,7 +744,7 @@ function dateOnly(ts: string | undefined): string {
   }
 }
 
-function buildTranscriptPage(path: string, session: ParsedSession): PageRecord {
+export function buildTranscriptPage(path: string, session: ParsedSession): PageRecord {
   const remote = resolveGitRemote(session.cwd);
   const slug_repo = repoSlug(remote);
   const date = dateOnly(session.start_time);
@@ -762,7 +762,7 @@ function buildTranscriptPage(path: string, session: ParsedSession): PageRecord {
   const stats = statSync(path);
   const sha = fileSha256(path);
 
-  const frontmatter = [
+  const fmLines = [
     "---",
     `agent: ${session.agent}`,
     `session_id: ${session.session_id}`,
@@ -773,10 +773,21 @@ function buildTranscriptPage(path: string, session: ParsedSession): PageRecord {
     `message_count: ${session.message_count}`,
     `tool_calls: ${session.tool_calls}`,
     `source_path: ${path}`,
-    session.partial ? "partial: true" : "",
-    "---",
-    "",
-  ].filter((l) => l !== "").join("\n");
+  ];
+  if (session.partial) fmLines.push("partial: true");
+  fmLines.push("---");
+  // The closing `---` fence MUST terminate its own line. session.body always
+  // starts with "## " (never a newline), so without the trailing "\n" the fence
+  // renders as `---## User`, which gray-matter/gbrain reject as a closer (the
+  // fence regex in gbrain markdown.ts requires `\n---(\r?\n|$)`). gbrain then
+  // scans to the next standalone `---` in the transcript, parses the prose
+  // between as YAML, and drops the whole page with "Invalid YAML frontmatter".
+  // A prior `.filter((l) => l !== "")` — added to drop the empty non-partial
+  // line — also stripped the blank that used to terminate the fence line, so
+  // every transcript whose body carries a later `---` horizontal rule silently
+  // failed to ingest. The explicit `+ "\n\n"` restores the fence newline plus a
+  // blank separator, matching the artifact-page branch in renderPageBody().
+  const frontmatter = fmLines.join("\n") + "\n\n";
 
   return {
     slug,
@@ -890,7 +901,7 @@ function gbrainAvailable(): boolean {
  * We do NOT set `slug:` in frontmatter — the staging-dir filename is the
  * source of truth and gbrain rejects mismatches.
  */
-function renderPageBody(page: PageRecord): string {
+export function renderPageBody(page: PageRecord): string {
   let body = page.body;
   if (body.startsWith("---\n")) {
     const end = body.indexOf("\n---", 4);
@@ -1314,6 +1325,49 @@ async function probeMode(args: CliArgs): Promise<ProbeReport> {
  *   redundant defense-in-depth and made it opt-in via `--scan-secrets`
  *   for users who want belt-and-suspenders.
  */
+/**
+ * Disambiguate colliding page slugs before staging (#2653).
+ *
+ * Two distinct source files can map to one transcript slug
+ * (transcripts/<agent>/<repo>/<date>-<session_id[:12]>): a session resumed
+ * under the same session_id on one day, or two session_ids sharing a 12-char
+ * prefix. writeStaged() names each file `${slug}.md`, so the second OVERWRITES
+ * the first — `written` counts both but only one lands on disk, gbrain collects
+ * N-1 of N, and the staged-vs-collected reconciliation guard (correctly) fails
+ * the whole batch. It repeats every run until the inputs age out of the window.
+ *
+ * Fix: keep the first occurrence's slug; give each later collider a stable
+ * `-<sha8(source_path)>` suffix. Deterministic (same source path → same slug
+ * across runs, so incremental dedup and gbrain's session_id dedup still line
+ * up) and it mutates slug + page_slug together so every downstream consumer
+ * (writeStaged, readNewFailures mapping, state recording) computes the same key.
+ *
+ * NOTE (Ryan-local, not upstream): this is a working-tree patch on top of the
+ * gstack install. `/gstack-upgrade` does `git reset --hard origin/main` and
+ * silently discards it. If the "accounted for N-1 of N staged" failure returns
+ * after an upgrade, re-apply this. See memory
+ * feedback_gstack_memory_ingest_slug_collision.
+ */
+export function disambiguateSlugs(pages: PreparedPage[]): void {
+  const seen = new Set<string>();
+  for (const p of pages) {
+    if (!seen.has(p.slug)) {
+      seen.add(p.slug);
+      continue;
+    }
+    const suffix = createHash("sha256").update(p.source_path).digest("hex").slice(0, 8);
+    let candidate = `${p.slug}-${suffix}`;
+    // Guarantee uniqueness even if a prior page already took the suffixed slug
+    // (two colliders sharing a source_path-hash prefix is astronomically
+    // unlikely, but a stuck source is not the place to trust luck).
+    let n = 1;
+    while (seen.has(candidate)) candidate = `${p.slug}-${suffix}-${n++}`;
+    seen.add(candidate);
+    p.slug = candidate;
+    p.page_slug = candidate;
+  }
+}
+
 function preparePages(
   args: CliArgs,
   ctx: WalkContext,
@@ -1477,6 +1531,11 @@ function preparePages(
     finalPrepared = finalPrepared.slice(0, args.limit);
   }
 
+  // Colliding path-derived slugs would overwrite in the staging dir, so two
+  // source files land as one page and the staged-vs-collected guard fails the
+  // whole batch every run (#2653). Disambiguate before staging.
+  disambiguateSlugs(finalPrepared);
+
   // Derived from the FINAL set: partial counts must describe pages that are
   // actually eligible and within the limit, not the whole scanned corpus.
   partialPages = finalPrepared.filter((p) => p.partial).length;
diff --git a/test/regression-transcript-frontmatter-fence.test.ts b/test/regression-transcript-frontmatter-fence.test.ts
new file mode 100644
index 0000000000..f4104c5e05
--- /dev/null
+++ b/test/regression-transcript-frontmatter-fence.test.ts
@@ -0,0 +1,65 @@
+/**
+ * Regression: transcript frontmatter fence must terminate its own line.
+ *
+ * buildTranscriptPage() emitted a closing `---` with no trailing newline, and
+ * session bodies always start with "## ", so the rendered page ended
+ * `...---## User`. gbrain's frontmatter matcher
+ * (`/^---\r?\n([\s\S]*?)\r?\n---(\r?\n|$)/`, src/core/markdown.ts) requires the
+ * closing `---` to end its own line, so it skipped the glued fence, latched onto
+ * the next standalone `---` in the transcript body, parsed the prose between as
+ * YAML, and dropped the whole page with "Invalid YAML frontmatter". Transcripts
+ * with no later `---` fell back to body-only (frontmatter silently lost).
+ */
+import { describe, it, expect } from "bun:test";
+import { mkdtempSync, writeFileSync, rmSync } from "fs";
+import { tmpdir } from "os";
+import { join } from "path";
+import {
+  parseTranscriptJsonl,
+  buildTranscriptPage,
+  renderPageBody,
+} from "../bin/gstack-memory-ingest";
+
+// The exact fence matcher gbrain uses (src/core/markdown.ts). Kept here so the
+// test fails if the rendered fence ever regresses.
+const GBRAIN_FENCE_RE = /^---\r?\n([\s\S]*?)\r?\n---(\r?\n|$)/;
+
+describe("regression: transcript frontmatter fence terminates its own line", () => {
+  it("keeps a body-embedded `---` out of the frontmatter block", () => {
+    const dir = mkdtempSync(join(tmpdir(), "gstack-fence-"));
+    const file = join(dir, "sess.jsonl");
+    // User content carries a markdown horizontal rule (`---`) followed by a
+    // colon-bearing line — exactly what the old glued fence swept into YAML.
+    const content =
+      `{"type":"user","message":{"role":"user","content":"before rule\\n\\n---\\n\\nnot: valid: yaml: here"},` +
+      `"timestamp":"2026-05-01T00:00:00Z","cwd":"${dir}"}\n` +
+      `{"type":"assistant","message":{"role":"assistant","content":"ok"},"timestamp":"2026-05-01T00:00:01Z"}\n`;
+    writeFileSync(file, content, "utf-8");
+
+    const session = parseTranscriptJsonl(file);
+    expect(session).not.toBeNull();
+    const page = buildTranscriptPage(file, session!);
+    const staged = renderPageBody(page);
+
+    // The fence is never glued onto the body.
+    expect(staged).not.toContain("---##");
+
+    // gbrain's matcher closes the frontmatter at the real fence, not at the
+    // horizontal rule deep in the transcript body.
+    const m = staged.match(GBRAIN_FENCE_RE);
+    expect(m).not.toBeNull();
+    const frontmatter = m![1];
+    expect(frontmatter).toContain("session_id:");
+    expect(frontmatter).toContain("title:");
+    // The body (headings, the HR, the colon-trap line) must NOT bleed into YAML.
+    expect(frontmatter).not.toContain("## User");
+    expect(frontmatter).not.toContain("not: valid: yaml: here");
+
+    // And the parsed body (after the fence's trailing blank line) is the
+    // session content, not YAML-absorbed prose.
+    const body = staged.slice(m![0].length);
+    expect(body.trimStart().startsWith("## User")).toBe(true);
+
+    rmSync(dir, { recursive: true, force: true });
+  });
+});
diff --git a/test/regression-transcript-slug-collision.test.ts b/test/regression-transcript-slug-collision.test.ts
new file mode 100644
index 0000000000..6591504491
--- /dev/null
+++ b/test/regression-transcript-slug-collision.test.ts
@@ -0,0 +1,65 @@
+/**
+ * Regression: disambiguateSlugs resolves colliding staged slugs.
+ *
+ * Two source files can map to one path-derived transcript slug (a session
+ * resumed under the same id on one day, or two session ids sharing a 12-char
+ * prefix). writeStaged() names each file `${slug}.md`, so the second overwrote
+ * the first; gbrain then collected N-1 of N staged files and the
+ * staged-vs-collected reconciliation guard failed the whole batch every run
+ * ("accounted for N-1 of N staged ... Refusing to advance state").
+ */
+import { describe, it, expect } from "bun:test";
+import { disambiguateSlugs } from "../bin/gstack-memory-ingest";
+
+const mk = (slug: string, source_path: string) => ({
+  slug,
+  source_path,
+  rendered_body: "---\ntitle: x\n---\n\nbody",
+  page_slug: slug,
+  partial: false,
+  type: "transcript" as const,
+  git_remote: undefined,
+});
+
+describe("regression: disambiguateSlugs resolves colliding staged slugs", () => {
+  it("keeps the first occurrence and suffixes later colliders deterministically", () => {
+    const slug = "transcripts/claude-code/repo/2026-08-25-abc123def456";
+    const run = () => {
+      const pages = [mk(slug, "/a.jsonl"), mk(slug, "/b.jsonl")];
+      disambiguateSlugs(pages);
+      return pages;
+    };
+    const pages = run();
+    // First keeps the clean slug; second is disambiguated.
+    expect(pages[0].slug).toBe(slug);
+    expect(pages[1].slug).not.toBe(slug);
+    expect(pages[1].slug.startsWith(slug + "-")).toBe(true);
+    // slug and page_slug move together (downstream consumers must agree).
+    expect(pages[1].page_slug).toBe(pages[1].slug);
+    // Deterministic across runs (same source path → same suffix).
+    expect(run()[1].slug).toBe(pages[1].slug);
+  });
+
+  it("gives every member of a 3-way collision a distinct slug", () => {
+    const slug = "transcripts/codex/repo/2026-08-25-deadbeefcafe";
+    const pages = [
+      mk(slug, "/one.jsonl"),
+      mk(slug, "/two.jsonl"),
+      mk(slug, "/three.jsonl"),
+    ];
+    disambiguateSlugs(pages);
+    const slugs = new Set(pages.map((p) => p.slug));
+    expect(slugs.size).toBe(3);
+    expect(pages[0].slug).toBe(slug);
+  });
+
+  it("leaves non-colliding slugs untouched", () => {
+    const pages = [
+      mk("transcripts/a/repo/2026-08-25-1111", "/x.jsonl"),
+      mk("transcripts/b/repo/2026-08-25-2222", "/y.jsonl"),
+    ];
+    const before = pages.map((p) => p.slug);
+    disambiguateSlugs(pages);
+    expect(pages.map((p) => p.slug)).toEqual(before);
+  });
+});