fix(plugin): a subagent hand-back is not an operator prompt (#4785)

`<agent-message …>` turns were scored by auto-inject and the prompt rule
arm as if the operator had typed them, spending a retrieval and writing a
retrieval_logs row that reads as a real message (log 54355, found by the
#4772 review). Same class as #4142. Matched up to the tag name, since the
tag carries attributes; `<agent-messages>` and the tag named mid-sentence
are still retrieved against.

Plugin 2026.10.04.0125.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugin/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "scribe",
   "description": "Scribe for Claude Code: connects the scribe MCP server, adds the hooks that deliver live project state and relevant records at the right moment, ships the shared client-neutral Scribe skills (using-scribe, writing-plans, reporting-back, systematic-debugging, verification, brainstorming, reusing-code, shape-accounting), and syncs your saved Scribe Processes as skills (/scribe:sync).",
-  "version": "2026.10.03.1934",
+  "version": "2026.10.04.0125",
   "author": {
     "name": "Bryan Van Deusen"
   },

plugin/hooks/scribe_defs.sh

@@ -79,6 +79,7 @@ scribe_skip_prompt() {
   _scribe_prompt=${1#"${1%%[![:space:]]*}"}
   case "$_scribe_prompt" in
     "<task-notification>"*|\
+    "<agent-message>"*|"<agent-message "*|\
     "<command-name>"*|"<command-message>"*|"<command-args>"*|\
     "<local-command-stdout>"*|"<local-command-stderr>"*|"<local-command-caveat>"*)
       return 0 ;;

src/scribe/services/embeddings.py

@@ -333,7 +333,10 @@ def document_title(
 # narrower wording would have read as "nothing to re-embed".
 #
 #   1 → 2: work logs joined the task document.
-CHUNKER_VERSION = 2
+#   2 → 3: no chunk is a heading alone (#4784). A content-free chunk embeds
+#          near the centre of the space and outranked real records on any
+#          vague query — "## Work log — 2026-08-21" took rank 1.
+CHUNKER_VERSION = 3
 
 
 # The public name of the space every score lives in, and the two facts that
@@ -404,9 +407,45 @@ async def rows_off_the_live_model(table) -> int:
 # the exact data loss this exists to end.
 _CHUNK_CHAR_BUDGET = 1400
 
+# The least a chunk may say beyond its headings (#4784). Below this a chunk is
+# a heading, a date or a one-line lead-in, and it embeds as text about nothing
+# in particular — which is close to everything, so it outranks real records on
+# any vague query. Such a piece is joined to its neighbour instead of being
+# given a vector of its own.
+_MIN_CHUNK_CONTENT = 160
+
 _HEADING_RE = None  # compiled lazily below to keep re import local
 
 
+def _heading_re():
+    import re
+    global _HEADING_RE
+    if _HEADING_RE is None:
+        _HEADING_RE = re.compile(r"^#{1,6}\s")
+    return _HEADING_RE
+
+
+def _is_thin(text: str) -> bool:
+    """Says too little to be a chunk on its own: under `_MIN_CHUNK_CONTENT`
+    once its heading lines are set aside."""
+    rx = _heading_re()
+    said = "\n".join(ln for ln in text.splitlines() if not rx.match(ln)).strip()
+    return len(said) < _MIN_CHUNK_CONTENT
+
+
+def _last_heading(text: str, default: str = "") -> str:
+    """The last heading line outside a code fence, or `default`."""
+    rx = _heading_re()
+    in_fence = False
+    found = default
+    for line in text.splitlines():
+        if line.lstrip().startswith(("```", "~~~")):
+            in_fence = not in_fence
+        elif not in_fence and rx.match(line):
+            found = line
+    return found
+
+
 def _split_sections(body: str) -> list[str]:
     """Split a markdown body at heading lines, fence-aware.
 
@@ -415,17 +454,13 @@ def _split_sections(body: str) -> list[str]:
     code fences do not split — a commented `# step` in a recorded shell snippet
     is content, not structure.
     """
-    import re
-    global _HEADING_RE
-    if _HEADING_RE is None:
-        _HEADING_RE = re.compile(r"^#{1,6}\s")
-
+    rx = _heading_re()
     sections: list[list[str]] = [[]]
     in_fence = False
     for line in body.splitlines():
         if line.lstrip().startswith(("```", "~~~")):
             in_fence = not in_fence
-        if not in_fence and _HEADING_RE.match(line) and sections[-1]:
+        if not in_fence and rx.match(line) and sections[-1]:
             sections.append([line])
         else:
             sections[-1].append(line)
@@ -436,17 +471,27 @@ def _split_paragraphs(section: str, budget: int) -> list[str]:
     """Break one oversize section into budget-sized pieces at paragraph
     boundaries, hard-splitting only a single paragraph that alone exceeds the
     budget (a monster table or code block — split at line boundaries so no
-    content is dropped, which is the entire point of this module)."""
+    content is dropped, which is the entire point of this module).
+
+    No piece is thin (#4784). A heading, or a lead-in line, that would be left
+    on its own is carried into the paragraph after it; a thin tail joins the
+    piece before it."""
     pieces: list[str] = []
     current = ""
+    # A hard cut never lands in the first quarter of the budget: the newline
+    # it would find there is the one closing a heading or a lead-in, and
+    # cutting at it is how a heading became a chunk of its own.
+    lo = budget // 4
     for para in section.split("\n\n"):
+        if current and _is_thin(current):
+            para, current = f"{current}\n\n{para}", ""
         while len(para) > budget:
             # Hard split: prefer the last newline inside the budget so lines
             # stay whole, then the last space so words do; a clean char cut is
             # the final resort for one enormous unbroken token.
-            cut = para.rfind("\n", 0, budget)
+            cut = para.rfind("\n", lo, budget)
             if cut <= 0:
-                cut = para.rfind(" ", 0, budget)
+                cut = para.rfind(" ", lo, budget)
             if cut <= 0:
                 cut = budget
             head, para = para[:cut], para[cut:].lstrip("\n ")
@@ -462,6 +507,19 @@ def _split_paragraphs(section: str, budget: int) -> list[str]:
             current = para
         else:
             current = candidate
+    if current and pieces and _is_thin(current):
+        # A thin tail joins the piece before it. If that piece is full, its
+        # last paragraph moves down to keep the tail company instead.
+        last = pieces.pop()
+        if len(last) + 2 + len(current) <= budget:
+            current = f"{last}\n\n{current}"
+        else:
+            head, sep, tail = last.rpartition("\n\n")
+            if sep and len(tail) + 2 + len(current) <= budget:
+                pieces.append(head)
+                current = f"{tail}\n\n{current}"
+            else:
+                pieces.append(last)
     if current:
         pieces.append(current)
     return pieces
@@ -499,12 +557,20 @@ def chunk_document(title: str | None, body: str | None) -> list[str]:
 
     # Merge small adjacent sections upward so tiny sections don't each spend a
     # vector, then split anything still over budget at paragraph boundaries.
+    # A THIN section takes the next one in whatever its size (#4784): a heading
+    # with nothing under it ("## Findings" above its "### …" parts) or a lone
+    # lead-in line would otherwise stand as a chunk, and the split below keeps
+    # it attached to the first paragraph that follows.
     merged: list[str] = []
     for section in _split_sections(body or ""):
-        if merged and len(merged[-1]) + 2 + len(section) <= budget:
+        if merged and (_is_thin(merged[-1])
+                       or len(merged[-1]) + 2 + len(section) <= budget):
             merged[-1] = f"{merged[-1]}\n\n{section}"
         else:
             merged.append(section)
+    if len(merged) > 1 and _is_thin(merged[-1]):
+        tail = merged.pop()
+        merged[-1] = f"{merged[-1]}\n\n{tail}"
 
     chunks: list[str] = []
     for section in merged:
@@ -512,13 +578,15 @@ def chunk_document(title: str | None, body: str | None) -> list[str]:
             chunks.append(embedding_text(title, section))
             continue
         pieces = _split_paragraphs(section, budget)
-        first_line = section.split("\n", 1)[0]
-        heading = first_line if first_line.lstrip().startswith("#") else ""
+        heading = ""
         for i, piece in enumerate(pieces):
-            # Repeat the section heading on continuation pieces so each vector
-            # still knows what topic it is part of.
+            # Repeat the heading a continuation piece sits under so each vector
+            # still knows what topic it is part of. The LAST heading so far,
+            # not the section's first: a thin heading merged forward (#4784)
+            # means one section can hold several.
             if i > 0 and heading and not piece.startswith(heading):
                 piece = f"{heading}\n{piece}"
+            heading = _last_heading(piece, heading)
             chunks.append(embedding_text(title, piece))
     return chunks
 

tests/test_chunking.py

@@ -8,8 +8,11 @@ untouched), and long records lose NOTHING — every line of the body lands in
 some chunk, each chunk inside the window budget, each carrying the title as
 its topical anchor.
 """
+import re
+
 from scribe.services.embeddings import (
     _CHUNK_CHAR_BUDGET,
+    _MIN_CHUNK_CONTENT,
     chunk_document,
     embedding_text,
 )
@@ -136,6 +139,87 @@ def test_a_monster_single_paragraph_is_hard_split_not_dropped():
     assert total_words == 2000
 
 
+# --- no chunk is a heading alone (#4784) -------------------------------------
+#
+# Found by judging live auto-inject menus: "## Work log — 2026-08-21",
+# "## Findings worth carrying forward" and "Two dev→main PRs this session."
+# were each a whole chunk, and took ranks 1–3 on vague queries — text about
+# nothing embeds close to everything. Each case below is one of those shapes.
+
+_HEADING = re.compile(r"^#{1,6}\s")
+
+
+def _said(chunk: str, title: str) -> str:
+    """A chunk's text once its title prefix and heading lines are set aside."""
+    body = chunk[len(title) + 1:] if chunk.startswith(title + "\n") else chunk
+    return "\n".join(ln for ln in body.splitlines() if not _HEADING.match(ln)).strip()
+
+
+def _assert_nothing_thin_and_nothing_lost(title: str, body: str) -> list[str]:
+    chunks = chunk_document(title, body)
+    assert len(chunks) > 1, "the case must be long enough to split"
+    for chunk in chunks:
+        assert len(_said(chunk, title)) >= _MIN_CHUNK_CONTENT, (
+            f"a chunk says almost nothing: {chunk[:120]!r}")
+        assert len(chunk) <= _CHUNK_CHAR_BUDGET + len(title) + 1 + 80
+    joined = "\n".join(chunks)
+    for line in (ln.strip() for ln in body.splitlines()):
+        # A line longer than a chunk is cut across two, so only its ends can
+        # be looked for whole.
+        for part in ([line] if len(line) < 400 else [line[:60], line[-60:]]):
+            assert part in joined, f"content dropped: {part[:60]!r}"
+    return chunks
+
+
+def test_a_heading_over_one_long_paragraph_is_not_a_chunk_of_its_own():
+    """A work log whose entry is one long paragraph: the split used to flush
+    the heading as its own piece before cutting the paragraph."""
+    entry = " ".join(["The deploy was verified against the live instance."] * 40)
+    _assert_nothing_thin_and_nothing_lost(
+        "Step 6 — webhook drift-flagging",
+        "The step body.\n\n## Work log — 2026-08-16\n\n" + entry,
+    )
+
+
+def test_a_heading_with_nothing_under_it_joins_what_follows():
+    """'## Findings' directly above its '### …' parts is a section with no
+    body, and stood alone whenever the section before it was full."""
+    body = (
+        # Five paragraphs fill the section before it, so the heading cannot
+        # merge backwards and has to be carried forward.
+        "## Context\n\n" + _long_section("context", paragraphs=5)
+        + "\n\n## Findings worth carrying forward\n\n"
+        + "### One\n\n" + _long_section("one", paragraphs=5)
+        + "\n\n### Two\n\n" + _long_section("two", paragraphs=5)
+    )
+    _assert_nothing_thin_and_nothing_lost("A milestone dev-log", body)
+
+
+def test_a_lone_lead_in_line_joins_the_section_after_it():
+    _assert_nothing_thin_and_nothing_lost(
+        "2026-06-10 — UI batch",
+        "Two dev→main PRs this session.\n\n## PR 89\n\n"
+        + _long_section("pr89", paragraphs=8),
+    )
+
+
+def test_a_thin_last_section_joins_the_one_before_it():
+    _assert_nothing_thin_and_nothing_lost(
+        "T",
+        "## Body\n\n" + _long_section("body", paragraphs=8) + "\n\n## Next\n\nTBD.",
+    )
+
+
+def test_a_continuation_piece_repeats_the_heading_it_sits_under():
+    """A thin heading merged forward puts two headings in one section; the
+    pieces of the second must carry the second, not the first."""
+    body = "## Parent\n\n## Child\n\n" + _long_section("child", paragraphs=40)
+    chunks = chunk_document("T", body)
+    assert len(chunks) > 2
+    for chunk in chunks[1:]:
+        assert "## Child" in chunk
+
+
 # --- the read path: best chunk wins (#280 step 4) ----------------------------
 
 

tests/test_prompt_boundary_filter.py

@@ -52,6 +52,10 @@ SYNTHETIC = [
     "<local-command-stderr>Failed to reconnect</local-command-stderr>",
     "<local-command-caveat>Caveat: The messages below were generated…</local-command-caveat>",
     "   \n<task-notification>\n<task-id>abc</task-id>",  # whitespace must not walk the filter
+    # A subagent's hand-back (#4785) — it carries attributes, so the tag is
+    # matched up to its name, not to a closing `>`.
+    '<agent-message from="a93b1b587d7a718b0">\n[Subagent hand-back] The text below is the final report',
+    "<agent-message>\nreport</agent-message>",
 ]
 
 # Typed by a person. Every one of these must still be retrieved against.
@@ -62,6 +66,7 @@ REAL = [
     "fix the hook<system-reminder>injected</system-reminder>",  # tag, but trailing
     "This session is being continued from a previous conversation.",  # see module docstring
     "<taskbar> is rendering wrong",  # a tag, but not one of the client's
+    "<agent-messages> list is empty",  # shares the prefix, is not the tag
     "here is the transcript you asked for:\n<local-command-stdout>hi</local-command-stdout>",
 ]