gstack-post: only a receipt above the first heading makes a full post (review fixes)

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

changelog.d/gsta195-prbody-intro.md

@@ -1,7 +1,7 @@
 **A partial `gstack-post pr-body` post keeps the PR's intro.** Since GST-412, any body file with a `## ` section replaced the text above the PR's first heading, so a lane that posted only `## Screenshots` deleted a human intro or a `Review-loop exception:` line under the receipt (GStack Minder: "a partial pr-body post must keep the human intro").
 
 ### Fixed
-- **Only a full post owns the text above the first heading.** A file with a `## ` section and a receipt block or its own lead text, as /ship composes it, still replaces stale lead text and stale notes under the receipt. A file with `## ` sections only keeps them.
+- **Only a full post owns the text above the first heading.** A file with a receipt block above its first `## ` section, as /ship composes it, still replaces stale lead text and stale notes under the receipt. Any other file keeps them; its own lead text still replaces the PR's lead text.
 
 ### Tests
-- `test/gstack-post.test.ts`: a partial post keeps the intro and the note under the receipt; the full-post cases now carry a receipt, as /ship's body does.
+- `test/gstack-post.test.ts`: a partial post keeps the intro and the note under the receipt, even with a caption of its own or a receipt further down; the full-post cases now carry a receipt, as /ship's body does.

docs/troubleshooting.md

@@ -2518,14 +2518,13 @@ same-titled section (title compared case-insensitively), the
 ````gstack-ship-receipt```` block is a section of its own so a receipt
 rewrite replaces only the receipt, sections the file does not rewrite stay in
 place, and new sections are appended after them. The text above the first
-`## ` heading belongs to the file when the file is a full post: a `## `
-section plus a receipt block or text of its own above its first heading, as
-/ship composes it. Then the current body's text there (the opening lines, and
+`## ` heading belongs to the file when the file is a full post: a
+receipt block above its first `## ` section, as /ship composes it. Then the current body's text there (the opening lines, and
 any lines between the receipt and the first heading, or the whole body when it
 has no `## ` heading) is replaced by the file's own text above its first
 heading, or dropped when the file has none. A partial post (`## ` sections
-only, such as a lane posting `## Screenshots`) and a file with no `## `
-section (a receipt-only or text-only post) leave that text alone, so a human
+with no receipt above them, such as a lane posting `## Screenshots`) and a
+file with no `## ` section (a receipt-only or text-only post) leave that text alone, so a human
 intro or a `Review-loop exception:` line under the receipt survives. One stderr line names what was replaced, kept, added
 and dropped, a dropped piece with its first line, or with that line withheld
 when the redaction scan flags it (`gstack-post: pr-body merged

lib/gstack-post.ts

@@ -9,9 +9,9 @@
  * `pr-body` merges by `## ` section into the PR's current body (read through
  * the same runner): a section in the file replaces the same-titled one, the
  * ship-receipt block is a section of its own, sections the file does not
- * rewrite are kept, new ones are appended, and a file with a `## ` section
- * plus a receipt or its own lead text replaces the text above the first
- * heading; `--replace` overwrites instead.
+ * rewrite are kept, new ones are appended, and a file with a receipt above
+ * its first `## ` section replaces the text above the first heading;
+ * `--replace` overwrites instead.
  * The scan runs on the merged bytes, which are the bytes sent.
  *
  * Exit codes: 0 posted; 1 HIGH finding (or oversize input) refused;
@@ -213,16 +213,16 @@ function splitSections(body: string): Section[] {
  * A file section whose title the current body holds more than once (an old
  * description pasted under the new one) matches no single section, so the
  * merge refuses instead of replacing one copy and keeping the stale other.
- * A full post (a file with at least one `## ` section and a receipt block or
- * text of its own above its first heading) manages the preamble (GST-412): every
+ * A full post (a file with a receipt block above its first `## ` section, as
+ * /ship composes it) manages the preamble (GST-412): every
  * non-blank text section before the current body's first heading (the leading
  * text, text after a receipt block) is dropped, the file's own text before its
  * first heading takes its place (leading text first, text after the file's
  * receipt right after the receipt), a dropped piece the file brings no text for
  * is listed in `dropped` with its first line (withheld when the redaction scan
  * flags it, since the merged bytes no longer hold it), and the receipt keeps the rules
- * above. A partial post (`## ` sections only) and a file without a `## `
- * section merge as described above, so the current intro is kept.
+ * above. Any other file (`## ` sections with no receipt above them, or no
+ * `## ` section) merges as described above, so the current intro is kept.
  */
 export function mergeBodySections(current: string, incoming: string): { body: string; replaced: string[]; kept: string[]; added: string[]; dropped: string[] } {
   const now = splitSections(current);
@@ -233,7 +233,8 @@ export function mergeBodySections(current: string, incoming: string): { body: st
     const end = list.findIndex(s => s.key.startsWith("h2:"));
     return list.slice(0, end < 0 ? list.length : end).filter(s => s.key.startsWith("text:") && s.text.trim() !== "");
   };
-  const managed = next.some(n => n.key.startsWith("h2:")) && (next.some(n => n.key === "receipt") || preamble(next).length > 0);
+  const firstHeading = next.findIndex(n => n.key.startsWith("h2:"));
+  const managed = firstHeading > 0 && next.slice(0, firstHeading).some(n => n.key === "receipt");
   const stale = managed ? preamble(now) : [];
   const ours = managed ? preamble(next) : [];
   const role = (s: Section) => (s.key === "text:lead" ? "lead" : "trailing");

test/gstack-post.test.ts

@@ -446,12 +446,12 @@ describe("gstack-post pr-body merges the PR body by section", () => {
     expect(after.stderr()).toBe("gstack-post: pr-body merged by section: replaced ship receipt, Why; kept unclosed receipt fence; added none\n");
   });
 
-  // Value: protects=a file with sections owns the text above the first heading (GST-412): stale lead text and stale text between the receipt and the
+  // Value: protects=a full post (a receipt above its first heading, as /ship composes it) owns the text above the first heading (GST-412): stale lead text and stale text between the receipt and the
   // first heading are dropped and named on stderr with their first line, the file's own preamble takes their place, a receipt-only or text-only file
   // keeps the older merge, a repost is byte-identical and an attribution callout is never doubled; fails_when=pr-body keeps a stale intro above the
   // receipt or a stale note under it after /ship reposts the sections; why_new=lead text was kept unless the file brought its own; seam=fake run;
   // no_claim=real gh
-  test("a file with sections replaces every text section above the current first heading and names each dropped piece", () => {
+  test("a full post replaces every text section above the current first heading and names each dropped piece", () => {
     const stale = withBody("Draft intro from gh pr create, long enough to need truncation in the summary line\nsecond line\n\n" + CURRENT, { "/b": RECEIPT("bbbb") + "\n## What changed\n\n- new\n" });
     expect(run(["pr-body", "5", "--body-file", "/b"], stale)).toBe(EXIT.posted);
     expect(sent(stale).input).toBe(RECEIPT("bbbb") + "\n## What changed\n\n- new\n\n## Why\n\nBecause.\n\n## Approvals\n\n- owner: do it\n");
@@ -469,8 +469,8 @@ describe("gstack-post pr-body merges the PR body by section", () => {
     expect(own.stderr()).toBe("gstack-post: pr-body merged by section: replaced leading text, ship receipt, trailing text, Why; kept none; added none\n");
   });
 
-  // Value: protects=a partial post (`## ` sections only, no receipt and no text of its own above its first heading) keeps the human intro and
-  //   the note under the receipt, the same as a full post that brings no replacement for them; fails_when=a lane posting only `## Screenshots`
+  // Value: protects=a partial post (no receipt above its first `## ` heading, even with a caption of its own or a receipt further down) keeps
+  //   the human intro and the note under the receipt; fails_when=a lane posting only `## Screenshots`
   //   deletes the intro or a Review-loop exception line; why_new=GST-412 made any file with a section own the preamble (GstackMinder,
   //   2026-10-31: "a partial pr-body post must keep the human intro"); seam=fake run; no_claim=real gh
   test("a partial post keeps the current intro and the note under the receipt", () => {
@@ -478,6 +478,12 @@ describe("gstack-post pr-body merges the PR body by section", () => {
     expect(run(["pr-body", "5", "--body-file", "/b"], partial)).toBe(EXIT.posted);
     expect(sent(partial).input).toBe("Human intro\n\n" + RECEIPT("aaaa") + "Review-loop exception: accepted by owner\n\n## What changed\n\n- old\n\n## Screenshots\n\n![shot](u)\n");
     expect(partial.stderr()).toBe("gstack-post: pr-body merged by section: replaced none; kept leading text, ship receipt, trailing text, What changed; added Screenshots\n");
+
+    for (const file of ["Screenshots below.\n\n## Screenshots\n\n![shot](u)\n", "## Screenshots\n\n![shot](u)\n\n" + RECEIPT("bbbb")]) {
+      const merged = mergeBodySections("Human intro\n\n" + RECEIPT("aaaa") + "Review-loop exception: accepted by owner\n\n## What changed\n\n- old\n", file);
+      expect(merged.body).toContain("Review-loop exception: accepted by owner");
+      expect(merged.dropped).toEqual([]);
+    }
   });
 
   // Value: protects=the dropped-piece excerpt on stderr never repeats a secret the merge removed from the body (the scan only reads the merged bytes);
@@ -515,11 +521,11 @@ describe("gstack-post pr-body merges the PR body by section", () => {
   });
 
   // Value: protects=--replace keeps the plain overwrite for a caller that composed the whole body, a current body with no H2 headings is kept as the leading
-  // section by a file without sections and dropped (and named) by a file with sections (GST-412), an empty current body posts the new body byte for byte,
+  // section by a file without sections and dropped (and named) by a full post (GST-412), an empty current body posts the new body byte for byte,
   // the scan runs on the merged bytes, and an unreadable current body is exit 3 with the --replace hint rather than an overwrite; fails_when=--replace
   // merges, headingless text is dropped by a receipt-only post or kept under new sections, the merge changes a lone new body, a secret in a kept section
   // passes the scan, or a failed read overwrites; why_new=first pr-body merge tests; seam=fake run; no_claim=real gh
-  test("--replace overwrites; a body without H2 headings is kept by a file without sections and dropped by one with sections; the merged bytes are what is scanned; a failed read refuses", () => {
+  test("--replace overwrites; a body without H2 headings is kept by a file without a receipt and dropped by a full post; the merged bytes are what is scanned; a failed read refuses", () => {
     const replaced = withBody(CURRENT, { "/b": "## What changed\n\nonly this\n" });
     expect(run(["pr-body", "5", "--replace", "--body-file", "/b"], replaced)).toBe(EXIT.posted);
     expect(sent(replaced).input).toBe("## What changed\n\nonly this\n");