feat(docs): save the whole chat session as a doc

Phase 75 (TODO.md L4): "Save as doc" now drafts a document from the
ENTIRE chat session — every question and answer up to the click, in
order — instead of only the clicked bubble's answer; the existing
doc-edit screen's free-form body editing is how the user edits out
anything they don't want to keep from previous replies (no new UI
surface).

Task 01 (frontend):
- app.js buildSessionTranscript(): walks the bor.chat.v1 conversation
  record in order — a numbered section per user turn ("## N.
  <question, raw>" + blank line + the raw answer text; more answers
  join under the same heading), sections blank-line separated, all
  trailing whitespace collapsed to one final newline. Only the raw
  persisted text travels (m.who + m.text — no thinking blocks, no
  source chips, no tune metadata); a brain record before the first
  user record is skipped; a heading-only section marks a user turn
  whose answer never landed (A6, owner-confirmed 2026-09-08).
- saveAsDoc(btn): the draft body is buildSessionTranscript(); the
  dead single-bubble markdown parameter is dropped (the button's
  appendSaveAsDocButton signature is unchanged — one button per
  bubble). Title/path/double-click guard/hand-off are unchanged
  (defaultDocTitle: the last question, whitespace-collapsed,
  <=120 chars; docs/<slug>.md).
- Unit: the app.js source pins move to the transcript shape (whole
  session, no thinking, no dead parameter).

Task 02 (E2E):
- tests/e2e/test_save_doc_session.py (bare-repo fixture, the
  phase-59 convention — git as source of truth): three DISTINCT
  on-topic turns in one session (turn 1 carries the phase-17
  "think out loud" trigger so its record has a thinking block the
  transcript must exclude) -> save on the LAST bubble -> the
  prefilled body is ## 1./## 2./## 3. in order, byte-exact against
  the deterministic mock, thinking-free -> edit the whole
  section-2 block out of the body -> push -> git show
  bor-docs:<path> equals the EDITED body byte-for-byte (section 2's
  question and answer provably absent; sections 1 and 3 byte-exact;
  the UI's sha prefix is git rev-parse bor-docs). Second test:
  the button on the FIRST bubble still drafts the whole session
  (A6 — the transcript is the session at click time, title stays
  the last question); canceling leaves the branch tip untouched.
- tests/e2e/test_response_to_docs.py: the phase-59 single-turn body
  expectation moves to the transcript shape ("## 1. <question>" +
  the answer's markdown) — the rest of the suite unchanged.

Also lands the phase-74 file moves (00_phase.md /
03_mock_marker_e2e.md -> complete/) and the phase reports — the
house convention of committing .agents/ with the phase.

frontend/assets/app.js

@@ -552,19 +552,24 @@ function markLastRetryable() {
  * answer, so m.stopped records never get it — the restore call site
  * gates on it). Gate: admin (the whoami gate Tune uses) AND a
  * configured docs repo (docsRepoConfigured — /api/config, settled in
- * the boot IIFE before any bubble renders). `markdown` is the RAW
- * persisted answer text — m.text on the restore path, the
- * done/fallback raw text on the live path — NEVER the rendered HTML.
+ * the boot IIFE before any bubble renders). `markdown` — the RAW
+ * persisted answer text, m.text on the restore path, the
+ * done/fallback raw text on the live path, NEVER the rendered HTML —
+ * stays in the signature (the three call sites are unchanged) but no
+ * longer travels: phase 75 (TODO L4, A6) drafts the WHOLE conversation
+ * from the `conversation` record at click time (buildSessionTranscript).
  * The .save-as-doc-btn's margin-inline-start: auto pushes it to the
  * row's right edge (the TODO's "bottom right"); markLastRetryable
  * keeps it rightmost when the last bubble also carries the Retry
  * button.
  *
- * Click: default title (the LAST user question, whitespace-collapsed,
- * ≤120 chars — the phase-50 auto-title convention) + default in-repo
- * path (docs/<slug>.md) → POST /api/doc-drafts {title, path, body} →
- * 201 → /doc-edit.html?draft=<token> (the edit screen, task 06, owns
- * the rest). Failure → the neutral one-line banner (phase-55
+ * Click: default title (UNCHANGED by phase 75 — the LAST user
+ * question, whitespace-collapsed, ≤120 chars, the phase-50 auto-title
+ * convention) + default in-repo path (docs/<slug>.md) + the
+ * FULL-SESSION transcript as the body (phase 75 A6) → POST
+ * /api/doc-drafts {title, path, body} → 201 →
+ * /doc-edit.html?draft=<token> (the edit screen, task 06, owns the
+ * rest). Failure → the neutral one-line banner (phase-55
  * convention), the conversation unblocked, no navigation. */
 const SAVE_AS_DOC_ICON =
   '<svg aria-hidden="true" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.7" stroke-linecap="round" stroke-linejoin="round"><path d="M14 3H6a1 1 0 0 0-1 1v16a1 1 0 0 0 1 1h12a1 1 0 0 0 1-1V8z"/><path d="M14 3v5h5"/><path d="M9 13h6M9 16h4"/></svg>';
@@ -603,6 +608,52 @@ function docSlug(title) {
   return slug || "note";
 }
 
+/* Phase 75 (TODO L4; A6, owner-confirmed 2026-09-08): the draft BODY
+ * is the WHOLE conversation — every user question and the brain
+ * answers that followed it, in order, as the RAW persisted text. The
+ * user edits out unwanted turns in the doc-edit body (A7 — the
+ * existing free-form body field; no new UI surface). The shape: a
+ * numbered section per USER turn —
+ *
+ *     ## 1. <user question, raw text>
+ *
+ *     <brain answer, raw text>
+ *
+ *     ## 2. <user question, raw text>
+ *
+ *     <brain answer, raw text>
+ *
+ * — 1-based per user turn (normally one answer per section; more
+ * answers join under the same heading), sections blank-line
+ * separated, ALL trailing whitespace collapsed to a single final
+ * newline. ONLY the raw text travels (m.who + m.text — nothing else
+ * off the record); a stopped/partial brain turn appears as-is (its
+ * text is what the user saw — A7); a brain record before the first
+ * user record (unproducible from the UI) is skipped, and a user turn
+ * whose brain record never landed is a heading-only section. */
+function buildSessionTranscript() {
+  const sections = []; // { heading: "## N. <q>", answers: [raw text] }
+  let open = null; // answers of the current user section (null while
+  // no user record has opened one yet)
+  for (const m of conversation) {
+    if (m.who === "user") {
+      open = [];
+      sections.push({
+        heading: `## ${sections.length + 1}. ${m.text}`,
+        answers: open,
+      });
+    } else if (open) {
+      open.push(m.text);
+    }
+  }
+  const body = sections
+    .map((s) =>
+      s.answers.length ? `${s.heading}\n\n${s.answers.join("\n\n")}` : s.heading
+    )
+    .join("\n\n");
+  return body.replace(/\s+$/, "") + "\n";
+}
+
 /* The bottom-right "Save as doc" button — the appendTuneButton
  * pattern: reuses the .msg-meta row when it exists (role=list → the
  * button joins as a listitem so ARIA stays valid), otherwise creates
@@ -623,15 +674,17 @@ function appendSaveAsDocButton(wrap, markdown) {
   btn.className = "save-as-doc-btn"; // margin-inline-start: auto → bottom-right
   if (meta.getAttribute("role") === "list") btn.setAttribute("role", "listitem");
   btn.innerHTML = SAVE_AS_DOC_ICON + "<span>Save as doc</span>";
-  btn.addEventListener("click", () => saveAsDoc(btn, markdown));
+  btn.addEventListener("click", () => saveAsDoc(btn));
   meta.appendChild(btn);
 }
 
-/* Create the draft from the bubble's RAW markdown and hand off to the
- * edit screen. Double-click guard: one save at a time (the button is
- * disabled until the outcome — released in the finally, never stale,
- * PLAN §7.4). */
-async function saveAsDoc(btn, markdown) {
+/* Create the draft from the FULL-SESSION transcript (phase 75 A6 —
+ * every Q/A up to the click, in order — replacing the phase-59
+ * single-bubble body; the title and path rules are unchanged) and
+ * hand off to the edit screen. Double-click guard: one save at a time
+ * (the button is disabled until the outcome — released in the
+ * finally, never stale, PLAN §7.4). */
+async function saveAsDoc(btn) {
   if (btn.disabled) return; // one save at a time (double-click guard)
   btn.disabled = true;
   try {
@@ -640,7 +693,7 @@ async function saveAsDoc(btn, markdown) {
     const res = await fetch("/api/doc-drafts", {
       method: "POST",
       headers: { "Content-Type": "application/json" },
-      body: JSON.stringify({ title, path, body: markdown }),
+      body: JSON.stringify({ title, path, body: buildSessionTranscript() }),
     });
     if (!res.ok) {
       // Neutral one-line copy (phase-55 convention) — the detail may