diff --git a/app/api/docs.py b/app/api/docs.py
index 717a8b2..3d12b75 100644
--- a/app/api/docs.py
+++ b/app/api/docs.py
@@ -4,6 +4,11 @@ GET /api/documents/content — one indexed document's full content (feeds the
 clickable document viewer, phase 10). DB-only by design: the (source, path)
 pair is looked up as a row, so there is no filesystem access and no
 path-traversal surface — ``../``-style values simply aren't rows (→ 404).
+
+PATCH /api/documents/summary — the admin summary editor (phase 57):
+update or clear ``documents.summary`` and re-embed the ``is_summary``
+chunk (embed first, mutate second — a failed LLM call leaves the row and
+chunk untouched; the content chunks are never re-embedded, D4).
 """
 from __future__ import annotations
 
@@ -13,10 +18,12 @@ from fastapi import APIRouter, Depends, HTTPException
 from sqlalchemy import func, select
 from sqlalchemy.orm import Session
 
+from app.api.sync import _sanitize_error
 from app.core.auth import require_admin
 from app.db import get_db
 from app.models import Chunk, Document
-from app.schemas import DocContent, DocList, DocSummary
+from app.rag.llm import EmbeddingError, LLMClient
+from app.schemas import DocContent, DocList, DocSummary, SummaryResult, SummaryUpdate
 
 router = APIRouter(tags=["kb"])
 
@@ -103,3 +110,71 @@ def get_document_content(
         indexed_at=doc.indexed_at.isoformat(),
         chunks=chunks,
     )
+
+
+@router.patch("/documents/summary", response_model=SummaryResult)
+async def update_document_summary(
+    payload: SummaryUpdate,
+    db: Session = Depends(get_db),  # noqa: B008
+    _admin: None = Depends(require_admin),  # noqa: B008
+) -> SummaryResult:
+    """Update or clear a document's stored summary and re-embed it.
+
+    Admin-only (phase 57, D4) — the document viewer itself stays
+    PUBLIC (phase 16 owner decision); only this edit affordance is
+    gated. The re-embed scope is the ``is_summary`` chunk only (D4):
+    the summary is the only text that changed, so the document's
+    content chunks keep their existing embeddings — the total chunk
+    count is unchanged by an update.
+
+    Fail-before-write (phase 57 locked decision): when the stripped
+    text is non-empty it is embedded **before** any DB mutation — an
+    embedding failure returns 503 with a sanitized ``detail`` naming
+    the failure (the ``ModelUnavailableError`` handling of
+    ``app/api/git_sources.py``) and leaves the row and chunk untouched.
+    An empty/whitespace-only ``summary`` clears instead:
+    ``documents.summary = NULL`` and the ``is_summary`` chunk (if any)
+    is deleted.
+    """
+    doc = db.scalar(
+        select(Document).where(
+            Document.source == payload.source, Document.path == payload.path
+        )
+    )
+    if doc is None:
+        raise HTTPException(status_code=404, detail="document not found")
+
+    summary_chunk = db.scalar(
+        select(Chunk).where(Chunk.document_id == doc.id, Chunk.is_summary.is_(True))
+    )
+    text = payload.summary.strip()
+    if text:
+        # Embed first, mutate second — a failed LLM call must never
+        # leave a half-updated row (phase 57 locked decision).
+        llm = LLMClient()
+        try:
+            vector = (await llm.embed([text]))[0]
+        except EmbeddingError as e:
+            raise HTTPException(status_code=503, detail=_sanitize_error(str(e))) from None
+        if summary_chunk is None:
+            # Markdown doc, or a phase-30 fail-soft import that indexed
+            # without a summary chunk — create the position −1 chunk.
+            summary_chunk = Chunk(document_id=doc.id, position=-1, is_summary=True)
+            db.add(summary_chunk)
+        summary_chunk.content = text
+        summary_chunk.embedding = vector
+        doc.summary = text
+    else:
+        if summary_chunk is not None:
+            db.delete(summary_chunk)
+        doc.summary = None
+    db.commit()
+    chunks = db.scalar(
+        select(func.count(Chunk.id))
+        .select_from(Document)
+        .outerjoin(Chunk, Chunk.document_id == Document.id)
+        .where(Document.id == doc.id)
+    ) or 0
+    return SummaryResult(
+        source=doc.source, path=doc.path, summary=doc.summary, chunks=chunks
+    )
diff --git a/app/schemas.py b/app/schemas.py
index 33418dd..62ea9c0 100644
--- a/app/schemas.py
+++ b/app/schemas.py
@@ -141,6 +141,40 @@ class DocContent(BaseModel):
     chunks: int
 
 
+class SummaryUpdate(BaseModel):
+    """``PATCH /api/documents/summary`` body (phase 57, task 01).
+
+    ``source`` / ``path`` name the indexed document (the same pair the
+    public ``GET /api/documents/content`` looks up); ``summary`` is the
+    raw new text. The API strips it before storing — an
+    empty/whitespace-only value is the *clear* operation (a first-class
+    action, phase 57 D4), not a 422. Unconstrained on purpose: unknown
+    pairs must 404 as "document not found" (row-lookup semantics),
+    exactly like the public content endpoint.
+    """
+
+    source: str
+    path: str
+    summary: str
+
+
+class SummaryResult(BaseModel):
+    """``PATCH /api/documents/summary`` response (phase 57, task 01).
+
+    ``summary`` is the stored text after the change (``null`` after a
+    clear — the viewer's summary box hides on null) and ``chunks`` the
+    document's post-change total chunk count: an update leaves the
+    content chunks untouched (the count is unchanged — only the single
+    ``is_summary`` chunk is replaced), a clear drops one (the
+    ``is_summary`` chunk is deleted).
+    """
+
+    source: str
+    path: str
+    summary: str | None
+    chunks: int
+
+
 class SteeringNoteIn(BaseModel):
     """``POST /api/steering`` body: one tuning instruction (phase 15).
 
diff --git a/frontend/assets/document.js b/frontend/assets/document.js
index 9bd12f1..7f5efa7 100644
--- a/frontend/assets/document.js
+++ b/frontend/assets/document.js
@@ -51,6 +51,15 @@
  * doc.summary renders as a labeled .doc-summary section above the
  * original content on BOTH surfaces (page + modal) through this one
  * core; the summary text is a text node (XSS contract unchanged).
+ *
+ * Phase 57 (task 02, D4): the panel gains an ADMIN-ONLY edit
+ * affordance (docAdminReady() gate on the module-cached whoami): an
+ * Edit button in the panel's header row opens an inline editor
+ * (prefilled textarea + Save/Cancel + a role=status live region), and
+ * Save PATCHes /api/documents/summary. The section is built for
+ * everyone exactly as phase 36 — the public viewer stays
+ * byte-for-byte identical (no button, no wiring, no admin-only
+ * network call) until the admin gate resolves true.
  */
 
 import { fetchIsAdmin, initSharedHeader } from "./header.js";
@@ -125,6 +134,14 @@ export function renderDocument(doc, { titleEl, metaEl, contentEl }) {
     body.textContent = doc.summary; // text node — XSS contract unchanged
     section.append(title, body);
     contentEl.appendChild(section);
+    // Phase 57 (task 02, D4): the section above is the phase-36 shape
+    // for EVERYONE — only an authenticated admin (docAdminReady(), the
+    // module-cached whoami promise) then gains the header row + Edit
+    // button + editor wiring. Anonymous / fetch failure: the panel is
+    // exactly what phase 36 built (byte-for-byte unchanged).
+    void docAdminReady().then((admin) => {
+      if (admin) wireSummaryEdit(section, doc);
+    });
   }
   if (doc.format === "md" || doc.format === "markdown") {
     const wrap = document.createElement("div");
@@ -139,6 +156,146 @@ export function renderDocument(doc, { titleEl, metaEl, contentEl }) {
   }
 }
 
+/* ---------- summary editing (phase 57, task 02 — D4, admin-only) ----------
+ * The .doc-summary panel is the ONE place the stored summary is edited
+ * (page + modal through this core). Only an admin (docAdminReady) ever
+ * gets the affordance; the public viewer is byte-for-byte unchanged. */
+
+/* The admin gate (D4 — the viewer stays public): the module-cached
+ * /api/whoami promise (header.js's fetchIsAdmin — the SAME single
+ * request per page the shared header already makes on every surface,
+ * so this adds no request of its own). A non-admin or any fetch
+ * failure resolves false → the anonymous viewer. */
+async function docAdminReady() {
+  try {
+    return (await fetchIsAdmin()) === true;
+  } catch {
+    return false;
+  }
+}
+
+/* The edit affordance on one rendered .doc-summary section. The bare
+ * h2 becomes a header row (label left, Edit button right). Edit swaps
+ * the .doc-summary-text node for the inline editor — a prefilled
+ * textarea (value, never innerHTML — XSS contract), Save / Cancel,
+ * and a role=status live region. Save PATCHes /api/documents/summary
+ * with { source, path, summary } — the pair comes from the doc object
+ * (the same values the modal core carries, document-modal.js). Success
+ * re-renders the text node via textContent and announces "Summary
+ * updated."; an empty save that clears announces "Summary cleared."
+ * and removes the panel a short beat later — the confirmation stays
+ * readable, and the renderer only draws the panel for non-empty
+ * summaries. Cancel restores the text node. A failure keeps the
+ * editor open with the user's text and shows neutral retry copy
+ * (phase-55 convention). */
+function wireSummaryEdit(section, doc) {
+  const title = section.querySelector(".doc-summary-title");
+  const body = section.querySelector(".doc-summary-text");
+  if (!title || !body) return;
+
+  /* Header row: label left, Edit button right (admin-only — the
+   * anonymous section keeps its bare h2). */
+  const head = document.createElement("div");
+  head.className = "doc-summary-head";
+  const editBtn = document.createElement("button");
+  editBtn.type = "button";
+  editBtn.className = "doc-summary-edit";
+  editBtn.textContent = "Edit";
+  head.append(title, editBtn);
+  section.replaceChildren(head, body);
+
+  /* Editor parts (built once; the textarea is rebuilt on every open so
+   * it always starts from the CURRENT stored summary). */
+  let editor = null;
+  const actions = document.createElement("div");
+  actions.className = "doc-summary-actions";
+  const saveBtn = document.createElement("button");
+  saveBtn.type = "button";
+  saveBtn.className = "doc-summary-save";
+  saveBtn.textContent = "Save";
+  const cancelBtn = document.createElement("button");
+  cancelBtn.type = "button";
+  cancelBtn.className = "doc-summary-cancel";
+  cancelBtn.textContent = "Cancel";
+  actions.append(saveBtn, cancelBtn);
+  const status = document.createElement("p");
+  status.className = "doc-summary-status";
+  status.setAttribute("role", "status");
+  status.setAttribute("aria-live", "polite");
+
+  /* Back to the display state: the text node re-rendered from the
+   * doc object (the CURRENT stored summary), the live region (the
+   * announced message), the Edit button available again. If the
+   * summary is gone (a clear landed while the editor was open — e.g.
+   * Cancel right after a successful empty save) the panel is gone
+   * too: the renderer only draws it for non-empty summaries. */
+  function closeEditor(message) {
+    status.textContent = message;
+    editBtn.hidden = false;
+    if (typeof doc.summary !== "string" || doc.summary.trim() === "") {
+      section.remove();
+      return;
+    }
+    body.textContent = doc.summary; // text node — the CURRENT stored summary
+    section.replaceChildren(head, body, status);
+    editBtn.focus();
+  }
+
+  async function saveSummary() {
+    const value = editor.value;
+    saveBtn.disabled = true; // one PATCH at a time (never stale)
+    status.textContent = "";
+    try {
+      const res = await fetch("/api/documents/summary", {
+        method: "PATCH",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ source: doc.source, path: doc.path, summary: value }),
+      });
+      if (!res.ok) {
+        // Neutral retry copy (phase-55 convention) — the user's text
+        // stays in the editor (the editor stays open on failure).
+        status.textContent = "Couldn't update the summary — try again.";
+        return;
+      }
+      const data = await res.json();
+      if (data.summary === null) {
+        // Cleared (D4): the panel disappears — the renderer only draws
+        // it for non-empty summaries. The live-region confirmation
+        // stays visible for a short beat before the panel leaves the
+        // DOM (a screen reader must be able to read it; the removal
+        // is a no-op if the surface re-rendered or closed meanwhile).
+        doc.summary = null;
+        status.textContent = "Summary cleared.";
+        setTimeout(() => section.remove(), 2000);
+        return;
+      }
+      doc.summary = data.summary;
+      closeEditor("Summary updated.");
+    } catch {
+      // Network failure: same neutral shape, the reachable? copy.
+      status.textContent = "Couldn't update the summary — is the app reachable?";
+    } finally {
+      saveBtn.disabled = false;
+    }
+  }
+
+  function openEditor() {
+    editor = document.createElement("textarea");
+    editor.className = "doc-summary-editor";
+    editor.value = typeof doc.summary === "string" ? doc.summary : ""; // value, never innerHTML
+    status.textContent = "";
+    editBtn.hidden = true;
+    section.replaceChildren(head, editor, actions, status);
+    editor.focus();
+  }
+
+  editBtn.addEventListener("click", openEditor);
+  saveBtn.addEventListener("click", () => {
+    void saveSummary();
+  });
+  cancelBtn.addEventListener("click", () => closeEditor(""));
+}
+
 /* ---------- /document.html page (phases 10/13/19) ----------
  * Phase 26: viewer-page-specific — see the import-safety note in the
  * header. The guard is #doc-title: it exists only on this page, so the
diff --git a/frontend/assets/styles.css b/frontend/assets/styles.css
index 62a339a..42e3af9 100644
--- a/frontend/assets/styles.css
+++ b/frontend/assets/styles.css
@@ -2382,6 +2382,97 @@ details.thinking .thinking-text ul { margin: 0 0 0.5rem; }
   color: var(--ink); /* on --surface ≈14.5:1 */
 }
 
+/* Summary edit affordance (phase 57, task 02 — D4, admin-only): the
+   header row (label + Edit button), the inline editor (prefilled
+   textarea + Save/Cancel + a role=status live region). House
+   dark-tech palette (phase-08 tokens), system fonts, no CDN;
+   :focus-visible via the global 3px outline rule. Anonymous visitors
+   never see any of it — the button and editor are wired only for
+   admins (docAdminReady in document.js), so the public panel is
+   byte-for-byte the phase-36 shape. */
+.doc-summary-head {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.75rem;
+  margin-bottom: 0.4rem; /* the old .doc-summary-title bottom margin */
+}
+.doc-summary-head .doc-summary-title { margin: 0; }
+.doc-summary-edit {
+  flex: 0 0 auto;
+  display: inline-flex;
+  align-items: center;
+  min-height: 24px;
+  padding: 0.15rem 0.7rem;
+  border: 1px solid var(--line);
+  border-radius: 999px;
+  background: transparent;
+  color: var(--ink-soft); /* 5.1:1 on --surface (AA) */
+  font: inherit;
+  font-weight: 600;
+  font-size: 0.78rem;
+  letter-spacing: 0.02em;
+  cursor: pointer;
+}
+.doc-summary-edit:hover { background: var(--brand-soft); color: var(--brand-ink); border-color: var(--brand); }
+.doc-summary-edit[hidden] { display: none; } /* the hidden attr must beat the display above */
+.doc-summary-editor {
+  display: block;
+  width: 100%;
+  min-height: 8rem;
+  padding: 0.6rem 0.8rem;
+  border: 1px solid var(--line);
+  border-radius: var(--radius-sm);
+  background: var(--bg); /* inset against the --surface panel */
+  color: var(--ink); /* 16.7:1 on --bg (AA) */
+  font: inherit;
+  line-height: 1.5;
+  resize: vertical;
+}
+.doc-summary-actions {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  margin-top: 0.75rem;
+}
+.doc-summary-save {
+  display: inline-flex;
+  align-items: center;
+  min-height: 32px;
+  padding: 0.35rem 0.95rem;
+  border: 0;
+  border-radius: 999px;
+  background: var(--brand);
+  color: var(--bg); /* --bg on --brand = 5.2:1 (AA) */
+  font: inherit;
+  font-weight: 600;
+  font-size: 0.85rem;
+  cursor: pointer;
+}
+.doc-summary-save:hover { background: #f55a72; } /* the house hover lightening */
+.doc-summary-save:disabled { opacity: 0.6; cursor: default; } /* one PATCH at a time */
+.doc-summary-cancel {
+  display: inline-flex;
+  align-items: center;
+  min-height: 32px;
+  padding: 0.35rem 0.95rem;
+  border: 1px solid var(--line);
+  border-radius: 999px;
+  background: transparent;
+  color: var(--ink-soft); /* 5.1:1 on --surface (AA) */
+  font: inherit;
+  font-weight: 600;
+  font-size: 0.85rem;
+  cursor: pointer;
+}
+.doc-summary-cancel:hover { background: var(--err-bg); color: var(--err-ink); border-color: var(--err-line); }
+.doc-summary-status {
+  margin: 0.6rem 0 0;
+  font-size: 0.85rem;
+  color: var(--ink-soft); /* 5.1:1 on --surface (AA) */
+}
+.doc-summary-status:empty { margin-top: 0; }
+
 /* Raw (non-markdown) formats: full-width mono pre, horizontal scroll. */
 .doc-raw {
   width: 100%;
diff --git a/tests/e2e/test_edit_summaries.py b/tests/e2e/test_edit_summaries.py
new file mode 100644
index 0000000..63ccd6e
--- /dev/null
+++ b/tests/e2e/test_edit_summaries.py
@@ -0,0 +1,430 @@
+"""Phase 57 E2E (Playwright): edit the AI-generated summary in the
+viewer — and watch it get re-embedded.
+
+TODO.md L4: "Be able to edit the summaries for documents in the RAG.
+Click an edit button in summary box and change the summary that the AI
+created. re-embed that document after changing the summary."
+Run in isolation (DB must be up: ``podman compose up -d db``):
+
+    uv run pytest tests/e2e/test_edit_summaries.py -v --no-cov
+
+The fixture KB is a story-dedicated directory
+(``tests/fixtures/summary_edit_kb/`` — the shared ``tests/fixtures/docs/``
+and the phase-30 ``summary_kb/`` stay pinned at their files) with ONE
+non-markdown A9 document:
+
+* ``quadlet/llamacpp.container`` — a podman quadlet unit (the
+  ``container`` extension is in the A9 default family, so the DEFAULT
+  import scope walks it — no ``BOR_IMPORT_EXTENSIONS`` override). At
+  import the mock ``lite`` model (``SUMMARY_MODE`` marker,
+  ``tests/e2e/mock_llm.py``) reduces it to the deterministic 24-token
+  digest — the first 24 tokens of the file, the header comment line —
+  stored on ``documents.summary`` and indexed as one ``is_summary``
+  chunk. The rest of the file is deliberately token-diluted
+  (config keys the digest never contains), and the sentinel
+  ``RESE-EDIT-SUMMARY-SENTINEL-b41d`` sits on the document's LAST line —
+  outside the 24-token digest — so the raw ``<pre>`` content is
+  distinguishable from the stored summary (the digest/sentinel mechanic
+  of ``tests/e2e/test_document_summaries.py``).
+
+DB isolation: the fixture's source name (``summary_edit_kb``) is
+distinctive — the suite never asserts on absolute row counts and
+deletes the rows it creates in a ``finally`` (other suites' documents
+stay untouched in the shared E2E database).
+
+The admin edits through the REAL browser flow (form login → the
+viewer's Edit button → the inline editor → Save); the re-embed itself
+is then verified against the live database (the chunk's NEW content, a
+FRESH non-NULL vector, the content chunks byte-for-byte untouched — the
+D4 re-embed scope) and against the public content endpoint (no cookie —
+the viewer stays public, phase 16).
+"""
+from __future__ import annotations
+
+import asyncio
+from collections.abc import Iterator
+from pathlib import Path
+from threading import Thread
+from typing import Any
+
+import httpx
+import pytest
+from playwright.sync_api import Page, expect
+from sqlalchemy import select
+
+from app.config import Settings
+from app.db import SessionLocal
+from app.models import Chunk, Document
+from app.rag.importer import ImportSummary, import_sources
+from app.rag.llm import LLMClient
+from e2e.auth_helpers import login
+from e2e.mock_llm import TOKEN_RE
+
+REPO = Path(__file__).resolve().parents[2]
+FIXTURES = REPO / "tests" / "fixtures" / "summary_edit_kb"
+SOURCE = FIXTURES.name  # "summary_edit_kb" — distinctive, never asserted by count
+DOC_PATH = "quadlet/llamacpp.container"
+#: Encoded viewer URL query value (slash → %2F, same as the chips /
+#: Sources table links build it).
+DOC_URL_PATH = "quadlet%2Fllamacpp.container"
+SENTINEL = "RESE-EDIT-SUMMARY-SENTINEL-b41d"
+
+#: The hand-edited summary (test 1) — a distinctive sentence no part of
+#: the fixture or its digest contains, so the round-trip assertion can
+#: never pass against the old text.
+NEW_SUMMARY = (
+    "Hand-edited: the quadlet unit serves the homelab's local model on "
+    "port 8081. (RESE-HANDEDIT-77ab)"
+)
+#: The modal-surface test's own edit (test 4) — likewise distinctive.
+MODAL_SUMMARY = (
+    "Edited from the modal: quadlet unit for the local inference server. "
+    "(RESE-MODAL-EDIT-3cd9)"
+)
+
+
+# --- Importer + thread helpers (test_document_summaries.py pattern) ---
+
+
+async def _import_fixtures(mock_port: int) -> ImportSummary:
+    kwargs: dict[str, Any] = {
+        "_env_file": None,
+        "llm_base_url": f"http://127.0.0.1:{mock_port}/v1",
+    }
+    settings = Settings(**kwargs)  # pyright: ignore[reportCallIssue]
+    return await import_sources([FIXTURES], LLMClient(settings))
+
+
+def _run_in_thread(coro: Any) -> Any:
+    """Run a coroutine on a worker thread.
+
+    Playwright's sync API keeps an asyncio loop running on the test thread,
+    so ``asyncio.run`` cannot be called directly from a test body.
+    """
+    box: dict[str, Any] = {}
+
+    def runner() -> None:
+        try:
+            box["value"] = asyncio.run(coro)
+        except BaseException as e:  # noqa: BLE001 — re-raised on the test thread
+            box["error"] = e
+
+    t = Thread(target=runner)
+    t.start()
+    t.join()
+    if "error" in box:
+        raise box["error"]
+    return box["value"]
+
+
+def _delete_source_rows() -> None:
+    """Delete every row of this suite's distinctive source (chunks
+    cascade with the document rows)."""
+    with SessionLocal() as db:
+        for doc in db.scalars(select(Document).where(Document.source == SOURCE)).all():
+            db.delete(doc)
+        db.commit()
+
+
+@pytest.fixture(autouse=True)
+def seeded_kb(mock_llm: int, db_ready: None) -> Iterator[ImportSummary]:
+    """Seed the story-dedicated fixture for one test (the DEFAULT import
+    scope — ``container`` is A9) and delete every row it creates
+    afterwards (DB isolation — see the module docstring)."""
+    _delete_source_rows()  # idempotent: leftovers from a crashed run
+    summary = _run_in_thread(_import_fixtures(mock_llm))
+    assert summary.formats == {"container": 1}
+    assert summary.added == 1
+    assert summary.summaries == 1 and summary.summary_errors == 0
+    assert summary.errors == 0
+    try:
+        yield summary
+    finally:
+        _delete_source_rows()
+
+
+def _expected_summary(content: str, source: str, path: str) -> str:
+    """The mock lite model's byte-stable digest + the code pointer line.
+
+    Mirrors ``mock_llm.compose_answer``'s ``SUMMARY_MODE`` branch (first
+    24 tokens of the document content) plus the summarizer's
+    deterministic ``Source:`` line — no model output is ever trusted.
+    """
+    digest = " ".join(TOKEN_RE.findall(content.lower())[:24])
+    return f"This document covers {digest}.\nSource: {source}/{path}"
+
+
+def _chunk_state() -> dict[str, Any]:
+    """The fixture document's DB state, read back through a fresh session.
+
+    ``total`` — the document's chunk count (never a table-wide count —
+    DB isolation); ``summary`` — ``documents.summary``; ``summary_*`` —
+    the single ``is_summary`` chunk (content + vector read-back);
+    ``raw_contents`` — the content chunks' text, sorted (the D4 pin:
+    the content chunks are byte-for-byte untouched by a summary edit).
+    """
+    with SessionLocal() as db:
+        doc = db.scalar(
+            select(Document).where(Document.source == SOURCE, Document.path == DOC_PATH)
+        )
+        assert doc is not None, "fixture doc was not imported"
+        chunks = db.scalars(select(Chunk).where(Chunk.document_id == doc.id)).all()
+    summary_chunks = [c for c in chunks if c.is_summary]
+    assert len(summary_chunks) <= 1, f"more than one is_summary chunk: {len(summary_chunks)}"
+    sc = summary_chunks[0] if summary_chunks else None
+    return {
+        "total": len(chunks),
+        "summary": doc.summary,
+        "summary_count": len(summary_chunks),
+        "summary_content": sc.content if sc else None,
+        "summary_vec": list(sc.embedding) if sc and sc.embedding is not None else None,
+        "raw_contents": sorted(c.content for c in chunks if not c.is_summary),
+    }
+
+
+def _api_summary(app_url: str) -> str | None:
+    """The public content endpoint's ``summary`` — NO cookie (the viewer
+    stays public, phase 16; a fresh httpx client carries no session)."""
+    r = httpx.get(
+        f"{app_url}/api/documents/content",
+        params={"source": SOURCE, "path": DOC_PATH},
+        timeout=10,
+    )
+    assert r.status_code == 200, r.text
+    return r.json()["summary"]
+
+
+def _doc_url(app_url: str) -> str:
+    return f"{app_url}/document.html?source={SOURCE}&path={DOC_URL_PATH}"
+
+
+# ---------------------------------------------------------------------------
+# 1. Admin: edit → Save → the panel, the API, and the DB all agree —
+#    and the is_summary chunk carries a FRESH embedding (D4 re-embed)
+# ---------------------------------------------------------------------------
+
+
+def test_admin_edits_summary(page: Page, app_url: str) -> None:
+    page.set_default_timeout(30_000)
+    content = (FIXTURES / DOC_PATH).read_text(encoding="utf-8")
+    assert SENTINEL in content.splitlines()[-1]  # last line, by design
+    expected = _expected_summary(content, SOURCE, DOC_PATH)
+    digest_line, pointer_line = expected.split("\n", 1)
+
+    before = _chunk_state()
+    assert before["summary"] == expected  # the mock digest is the stored summary
+    assert before["summary_count"] == 1
+    assert before["summary_vec"] is not None
+
+    login(page, app_url)
+    page.goto(_doc_url(app_url))
+
+    # The .doc-summary panel shows the digest (digest + pointer lines) —
+    # and nothing from the diluted raw body ("PublishPort" is deeper in
+    # the file, outside the 24-token digest).
+    panel = page.locator(".doc-summary")
+    expect(panel).to_have_count(1)
+    expect(panel).to_be_visible()
+    expect(panel.locator(".doc-summary-title")).to_have_text("Summary")
+    expect(panel).to_contain_text(digest_line)
+    expect(panel).to_contain_text(pointer_line)
+    expect(panel).not_to_contain_text("PublishPort")
+    # The original still renders below, sentinel and all.
+    expect(page.locator("#doc-content pre.doc-raw")).to_contain_text(SENTINEL)
+
+    # The admin-only Edit button (phase 57, D4 — the viewer itself is
+    # public; only the affordance is gated).
+    edit = panel.locator(".doc-summary-edit")
+    expect(edit).to_be_visible()
+    expect(edit).to_have_text("Edit")
+
+    # Edit → inline editor: textarea PREFILLED with the current summary,
+    # Save / Cancel, and the role=status live region.
+    edit.click()
+    editor = page.locator(".doc-summary-editor")
+    expect(editor).to_be_visible()
+    expect(editor).to_have_value(expected)
+    expect(page.locator(".doc-summary-save")).to_be_visible()
+    expect(page.locator(".doc-summary-cancel")).to_be_visible()
+    status = page.locator(".doc-summary-status")
+    expect(status).to_have_attribute("role", "status")
+    expect(status).to_have_attribute("aria-live", "polite")
+
+    # Replace the text with the distinctive hand-edit and Save.
+    page.fill(".doc-summary-editor", NEW_SUMMARY)
+    page.click(".doc-summary-save")
+
+    # Live-region confirmation, and the panel text is the NEW summary
+    # (re-rendered through the textContent contract — the digest is gone).
+    expect(status).to_have_text("Summary updated.")
+    expect(panel.locator(".doc-summary-text")).to_have_text(NEW_SUMMARY)
+    expect(panel).not_to_contain_text(digest_line)
+
+    # Public read (no cookie): the content endpoint serves the new text.
+    assert _api_summary(app_url) == NEW_SUMMARY
+
+    # The re-embed, verified in the DB (D4): the is_summary chunk's
+    # content is the new text with a FRESH non-NULL vector; the total
+    # chunk count is unchanged and the content chunks are byte-for-byte
+    # untouched — only the summary changed, so only it was re-embedded.
+    after = _chunk_state()
+    assert after["total"] == before["total"]  # count unchanged by an update
+    assert after["summary_count"] == 1
+    assert after["summary"] == NEW_SUMMARY
+    assert after["summary_content"] == NEW_SUMMARY
+    assert after["summary_vec"] is not None  # re-embedded, non-NULL
+    assert after["summary_vec"] != before["summary_vec"]  # a FRESH vector
+    assert after["raw_contents"] == before["raw_contents"]  # content chunks untouched
+
+
+# ---------------------------------------------------------------------------
+# 2. Admin: an empty save CLEARS — the panel disappears, summary NULL,
+#    the is_summary chunk row is gone (count −1)
+# ---------------------------------------------------------------------------
+
+
+def test_admin_clears_summary(page: Page, app_url: str) -> None:
+    page.set_default_timeout(30_000)
+    content = (FIXTURES / DOC_PATH).read_text(encoding="utf-8")
+    expected = _expected_summary(content, SOURCE, DOC_PATH)
+
+    before = _chunk_state()
+    assert before["summary"] == expected
+    assert before["summary_count"] == 1
+
+    login(page, app_url)
+    page.goto(_doc_url(app_url))
+    panel = page.locator(".doc-summary")
+    expect(panel).to_have_count(1)
+    expect(panel.locator(".doc-summary-edit")).to_be_visible()
+
+    # Select-all + delete — clear the prefilled editor — then Save.
+    panel.locator(".doc-summary-edit").click()
+    page.fill(".doc-summary-editor", "")
+    page.click(".doc-summary-save")
+
+    # "Summary cleared." in the live region, then the panel leaves the
+    # DOM (the renderer only draws it for non-empty summaries — the
+    # removal lands a short beat after the confirmation). The original
+    # content below is untouched.
+    expect(page.locator(".doc-summary-status")).to_have_text("Summary cleared.")
+    expect(page.locator(".doc-summary")).to_have_count(0, timeout=8_000)
+    expect(page.locator("#doc-content pre.doc-raw")).to_contain_text(SENTINEL)
+
+    # The public endpoint now reports no summary…
+    assert _api_summary(app_url) is None
+
+    # …and the DB agrees: summary NULL, the is_summary row deleted
+    # (count −1), the content chunks byte-for-byte untouched.
+    after = _chunk_state()
+    assert after["total"] == before["total"] - 1  # the is_summary chunk is gone
+    assert after["summary"] is None
+    assert after["summary_count"] == 0
+    assert after["summary_vec"] is None
+    assert after["raw_contents"] == before["raw_contents"]
+
+
+# ---------------------------------------------------------------------------
+# 3. Anonymous: the digest renders, but no Edit button — and the
+#    endpoint is 403 (the public viewer is byte-for-byte phase 36)
+# ---------------------------------------------------------------------------
+
+
+def test_anonymous_cannot(page: Page, app_url: str) -> None:
+    page.set_default_timeout(30_000)
+    content = (FIXTURES / DOC_PATH).read_text(encoding="utf-8")
+    expected = _expected_summary(content, SOURCE, DOC_PATH)
+    digest_line, _ = expected.split("\n", 1)
+
+    # Fresh context (the function-scoped page fixture — no login): the
+    # panel renders the digest, but the edit affordance is ABSENT — no
+    # button, no header row, no editor wiring. The section keeps the
+    # phase-36 byte-for-byte shape: a bare h2 + the text-node <p>.
+    page.goto(_doc_url(app_url))
+    panel = page.locator(".doc-summary")
+    expect(panel).to_have_count(1)
+    expect(panel).to_be_visible()
+    expect(panel).to_contain_text(digest_line)
+    expect(page.locator(".doc-summary-edit")).to_have_count(0)
+    expect(page.locator(".doc-summary-head")).to_have_count(0)
+    expect(page.locator(".doc-summary-editor")).to_have_count(0)
+    children = page.evaluate(
+        "() => [...document.querySelector('.doc-summary').children]"
+        ".map((el) => el.className)"
+    )
+    assert children == ["doc-summary-title", "doc-summary-text"], (
+        f"anonymous panel drifted from the phase-36 shape: {children}"
+    )
+
+    # The endpoint is admin-gated (D4): an anonymous PATCH → 403
+    # "admin only" (a fresh httpx client carries no session), and the
+    # stored summary is untouched.
+    r = httpx.patch(
+        f"{app_url}/api/documents/summary",
+        json={"source": SOURCE, "path": DOC_PATH, "summary": "not allowed"},
+        timeout=10,
+    )
+    assert r.status_code == 403
+    assert r.json() == {"detail": "admin only"}
+    assert _chunk_state()["summary"] == expected  # untouched
+
+
+# ---------------------------------------------------------------------------
+# 4. Modal surface: the SAME shared renderer — the Sources-page modal
+#    carries the Edit button too, and a save from it round-trips
+# ---------------------------------------------------------------------------
+
+
+def test_admin_modal_surface_edit(page: Page, app_url: str) -> None:
+    """One core, two surfaces (phase 26/36): the document modal from the
+    Sources table renders through the SAME ``renderDocument`` — so the
+    admin gets the Edit button in the modal as well, and a save from
+    there hits the same endpoint + DB row (the page test is unchanged
+    in shape; this pins the second surface)."""
+    page.set_default_timeout(30_000)
+    content = (FIXTURES / DOC_PATH).read_text(encoding="utf-8")
+    expected = _expected_summary(content, SOURCE, DOC_PATH)
+    digest_line, _ = expected.split("\n", 1)
+
+    before = _chunk_state()
+    assert before["summary"] == expected
+
+    login(page, app_url)  # lands on /sources.html (the catalog is admin-only)
+    row = page.locator("#docs-tbody tr", has_text=DOC_PATH)
+    expect(row).to_have_count(1)
+    before_tabs = len(page.context.pages)
+    row.locator("td:nth-child(2) a.doc-link").click()
+    assert len(page.context.pages) == before_tabs, "row link must not open a new tab"
+
+    # The modal shows the panel with the digest + the admin Edit button.
+    expect(page.locator(".doc-modal")).to_be_visible()
+    expect(page.locator("#doc-modal-title")).to_have_text("llamacpp")
+    modal_panel = page.locator("#doc-modal .doc-summary")
+    expect(modal_panel).to_have_count(1)
+    expect(modal_panel).to_be_visible()
+    expect(modal_panel).to_contain_text(digest_line)
+    edit = modal_panel.locator(".doc-summary-edit")
+    expect(edit).to_be_visible()
+
+    # Edit → prefilled editor → replace → Save → the modal's panel
+    # reflects the new text and the live region confirms.
+    edit.click()
+    editor = page.locator("#doc-modal .doc-summary-editor")
+    expect(editor).to_be_visible()
+    expect(editor).to_have_value(expected)
+    page.fill("#doc-modal .doc-summary-editor", MODAL_SUMMARY)
+    page.click("#doc-modal .doc-summary-save")
+    expect(page.locator("#doc-modal .doc-summary-status")).to_have_text("Summary updated.")
+    expect(modal_panel.locator(".doc-summary-text")).to_have_text(MODAL_SUMMARY)
+
+    # Same endpoint, same DB row: the public read and the chunk agree —
+    # count unchanged, fresh vector, content chunks untouched.
+    assert _api_summary(app_url) == MODAL_SUMMARY
+    after = _chunk_state()
+    assert after["total"] == before["total"]
+    assert after["summary_count"] == 1
+    assert after["summary"] == MODAL_SUMMARY
+    assert after["summary_content"] == MODAL_SUMMARY
+    assert after["summary_vec"] is not None
+    assert after["summary_vec"] != before["summary_vec"]
+    assert after["raw_contents"] == before["raw_contents"]
diff --git a/tests/fixtures/summary_edit_kb/quadlet/llamacpp.container b/tests/fixtures/summary_edit_kb/quadlet/llamacpp.container
new file mode 100644
index 0000000..a0a4459
--- /dev/null
+++ b/tests/fixtures/summary_edit_kb/quadlet/llamacpp.container
@@ -0,0 +1,22 @@
+# llama.cpp quadlet container — the homelab local LLM inference server
+[Unit]
+Description=llama.cpp server for local inference (qwen3-8b)
+Requires=llamacpp-network.net
+After=network-online.target
+
+[Container]
+Image=docker.io/ggml-org/llama-cpp:0.1.43
+ContainerName=llamacpp
+Network=llamacpp-network
+PublishPort=8081:8080
+Volume=/srv/llama/models:/models:ro
+Environment=CONTEXT_LENGTH=32768
+Environment=BATCH_SIZE=512
+Restart=always
+
+[Service]
+TimeoutStartSec=300
+
+[Install]
+WantedBy=default.target
+# RESE-EDIT-SUMMARY-SENTINEL-b41d — phase 57 fixture marker: last line, outside the 24-token digest.
diff --git a/tests/integration/test_document_content.py b/tests/integration/test_document_content.py
index dbf1691..687ebe3 100644
--- a/tests/integration/test_document_content.py
+++ b/tests/integration/test_document_content.py
@@ -1,19 +1,40 @@
-"""Integration tests: GET /api/documents/content — the viewer's data source.
+"""Integration tests: the document-content API — the viewer's data source.
 
 Uses the real compose Postgres (``db`` fixture) and FastAPI's TestClient:
-* 200 with the full field set for a seeded document (all formats);
-* ``summary`` surfaced for summarized docs, ``null`` for markdown (phase 36);
-* anonymous access stays 200 (phase 16 soft rule — public viewer);
-* 404 for an unknown (source, path) pair;
-* 404 for traversal-style ``path`` values (no filesystem access → no leak).
+* GET: 200 with the full field set for a seeded document (all formats);
+* GET: ``summary`` surfaced for summarized docs, ``null`` for markdown
+  (phase 36);
+* GET: anonymous access stays 200 (phase 16 soft rule — public viewer);
+* GET: 404 for an unknown (source, path) pair;
+* GET: 404 for traversal-style ``path`` values (no filesystem access → no
+  leak).
+
+PATCH /api/documents/summary (phase 57, task 01) — the admin summary
+editor, on the same DB-backed fixtures:
+* update: ``documents.summary`` + the ``is_summary`` chunk's content
+  replaced, fresh embedding, content chunks untouched (count unchanged —
+  D4 re-embed scope);
+* clear: empty/whitespace text → ``summary`` NULL + ``is_summary`` chunk
+  deleted (idempotent, no embed call);
+* markdown doc (no prior ``is_summary`` chunk) → one created at
+  position −1 with the new embedding;
+* 404 unknown (source, path) (incl. traversal strings); 403 anonymous;
+* embed failure → 503 sanitized detail, DB byte-for-byte untouched
+  (fail-before-write — embed before any mutation).
 """
 from __future__ import annotations
 
 from datetime import UTC, datetime
 
-from sqlalchemy import text
+import pytest
+from fastapi.testclient import TestClient
+from sqlalchemy import select, text
+from sqlalchemy.orm import Session
 
+import app.api.docs as docs_api
 from app.models import Chunk, Document
+from app.rag.llm import EmbeddingError
+from tests.fakes import FakeEmbedder
 
 
 def _seed_doc(
@@ -24,8 +45,14 @@ def _seed_doc(
     content: str = "# Kubernetes\n\nTalos on 3 nodes.",
     chunks: int = 2,
     summary: str | None = None,
+    summary_chunk: bool = False,
 ) -> None:
-    """Truncate the KB and insert one document with ``chunks`` chunk rows."""
+    """Truncate the KB and insert one document with ``chunks`` chunk rows.
+
+    ``summary_chunk`` additionally indexes the phase-30 ``is_summary``
+    chunk at position −1 with the seeded vector (requires ``summary`` —
+    the phase-30 invariant: the chunk mirrors ``documents.summary``).
+    """
     db.execute(text("TRUNCATE chunks, documents"))
     db.commit()
     doc = Document(
@@ -45,9 +72,324 @@ def _seed_doc(
             Chunk(document_id=doc.id, position=i, content=f"chunk {i}", embedding=[0.01] * 768)
             for i in range(chunks)
         )
+    if summary_chunk:
+        assert summary is not None
+        db.add(
+            Chunk(
+                document_id=doc.id,
+                position=-1,
+                content=summary,
+                embedding=[0.01] * 768,
+                is_summary=True,
+            )
+        )
     db.commit()
 
 
+# ---------------------------------------------------------------------------
+# PATCH /api/documents/summary (phase 57, task 01)
+# ---------------------------------------------------------------------------
+
+
+class _DeadEmbedder:
+    """An ``LLMClient`` stand-in whose ``embed`` always fails — the
+    dead-endpoint path (phase 57 fail-before-write). The message mirrors
+    ``LLMClient.embed``'s transport wrap, with embedded credentials that
+    the sanitizer must mask."""
+
+    def __init__(self) -> None:
+        self.calls: list[list[str]] = []
+
+    async def embed(self, texts: list[str]) -> list[list[float]]:
+        self.calls.append(list(texts))
+        raise EmbeddingError(
+            "embeddings request to https://user:secret@aipi.example.com/v1 "
+            "failed: connection refused"
+        )
+
+
+def _seed_yaml_doc(db, *, summary: str, summary_chunk: bool) -> None:
+    """One phase-30-style non-markdown doc: 2 content chunks + (optionally)
+    its ``is_summary`` chunk."""
+    _seed_doc(
+        db,
+        path="container_gitlab/gitlab-compose.yaml",
+        title="gitlab-compose",
+        content="services:\n  gitlab:\n    image: gitlab/gitlab-ce",
+        summary=summary,
+        summary_chunk=summary_chunk,
+    )
+
+
+def _doc_id(db, path: str):
+    return db.scalar(select(Document.id).where(Document.path == path))
+
+
+def _chunk_snapshots(db, doc_id) -> dict:
+    """``{chunk id: (position, content, embedding, is_summary)}``.
+
+    Before/after comparisons prove exactly which rows a PATCH touched.
+    Embeddings are compared read-back to read-back: pgvector stores
+    float4, so raw Python floats do not round-trip exactly (the house
+    style elsewhere is ``is not None`` + dimension checks)."""
+    rows = db.scalars(select(Chunk).where(Chunk.document_id == doc_id)).all()
+    return {
+        c.id: (
+            c.position,
+            c.content,
+            list(c.embedding) if c.embedding is not None else None,
+            c.is_summary,
+        )
+        for c in rows
+    }
+
+
+def test_summary_patch_update_reembeds_summary_chunk(
+    admin_client: TestClient, client: TestClient, monkeypatch: pytest.MonkeyPatch, db: Session
+) -> None:
+    """Admin PATCH with new text (phase 57, D4): ``documents.summary`` and
+    the ``is_summary`` chunk's content are replaced and the chunk gets a
+    fresh embedding — in place (same row id); the content chunks are
+    untouched (same ids, positions, contents, vectors) and the total
+    count is unchanged. One ``embed`` call, only with the new text."""
+    old = "GitLab CE runs in a Podman compose stack on the homelab NAS."
+    new = "GitLab CE is now backed by external PostgreSQL and MinIO."
+    _seed_yaml_doc(db, summary=old, summary_chunk=True)
+    doc_id = _doc_id(db, "container_gitlab/gitlab-compose.yaml")
+    db.expire_all()
+    before = _chunk_snapshots(db, doc_id)
+    assert len(before) == 3
+    try:
+        fake = FakeEmbedder()
+        monkeypatch.setattr(docs_api, "LLMClient", lambda: fake)
+        r = admin_client.patch(
+            "/api/documents/summary",
+            json={
+                "source": "Homelab",
+                "path": "container_gitlab/gitlab-compose.yaml",
+                "summary": new,
+            },
+        )
+        assert r.status_code == 200, r.text
+        body = r.json()
+        assert set(body) == {"source", "path", "summary", "chunks"}
+        assert body["source"] == "Homelab"
+        assert body["path"] == "container_gitlab/gitlab-compose.yaml"
+        assert body["summary"] == new
+        assert body["chunks"] == 3  # 2 content + 1 is_summary — unchanged by an update
+
+        db.expire_all()
+        row = db.get(Document, doc_id)
+        assert row is not None
+        assert row.summary == new
+        after = _chunk_snapshots(db, doc_id)
+        assert set(after) == set(before)  # same rows: nothing added or deleted
+        sc = next(cid for cid, v in after.items() if v[3])
+        assert sc in before  # replaced in place — the same row id
+        pos, content, vec, _ = after[sc]
+        assert pos == -1
+        assert content == new
+        assert vec is not None and len(vec) == 768
+        assert vec != before[sc][2]  # fresh embedding, not the seeded one
+        for cid, v in after.items():
+            if not v[3]:
+                assert v == before[cid]  # content chunks untouched, byte for byte
+        assert fake.calls == [[new]]  # one embed call, the new text only
+        # The public viewer's data source now carries the new summary
+        # verbatim (anonymous — the viewer stays public, phase 16).
+        g = client.get(
+            "/api/documents/content",
+            params={"source": "Homelab", "path": "container_gitlab/gitlab-compose.yaml"},
+        )
+        assert g.status_code == 200
+        assert g.json()["summary"] == new
+    finally:
+        db.execute(text("TRUNCATE chunks, documents"))
+        db.commit()
+
+
+def test_summary_patch_clear(
+    admin_client: TestClient, monkeypatch: pytest.MonkeyPatch, db: Session
+) -> None:
+    """PATCH with empty/whitespace text clears (phase 57, D4):
+    ``documents.summary`` → NULL and the ``is_summary`` chunk is deleted;
+    the content chunks are untouched. A second clear is an idempotent 200
+    and clearing never calls the embedder."""
+    old = "GitLab CE runs in a Podman compose stack on the homelab NAS."
+    _seed_yaml_doc(db, summary=old, summary_chunk=True)
+    doc_id = _doc_id(db, "container_gitlab/gitlab-compose.yaml")
+    db.expire_all()
+    before = _chunk_snapshots(db, doc_id)
+    assert len(before) == 3
+    try:
+        fake = FakeEmbedder()
+        monkeypatch.setattr(docs_api, "LLMClient", lambda: fake)
+        for body_summary in ("   ", ""):  # whitespace, then a true empty string
+            r = admin_client.patch(
+                "/api/documents/summary",
+                json={
+                    "source": "Homelab",
+                    "path": "container_gitlab/gitlab-compose.yaml",
+                    "summary": body_summary,
+                },
+            )
+            assert r.status_code == 200, r.text
+            assert r.json() == {
+                "source": "Homelab",
+                "path": "container_gitlab/gitlab-compose.yaml",
+                "summary": None,
+                "chunks": 2,
+            }
+        db.expire_all()
+        row = db.get(Document, doc_id)
+        assert row is not None
+        assert row.summary is None
+        after = _chunk_snapshots(db, doc_id)
+        assert len(after) == 2  # the is_summary chunk row is gone (count −1)
+        for cid, v in after.items():
+            assert not v[3]
+            assert v == before[cid]  # content chunks untouched, byte for byte
+        assert fake.calls == []  # clearing never embeds
+    finally:
+        db.execute(text("TRUNCATE chunks, documents"))
+        db.commit()
+
+
+def test_summary_patch_markdown_doc_creates_summary_chunk(
+    admin_client: TestClient, monkeypatch: pytest.MonkeyPatch, db: Session
+) -> None:
+    """A markdown doc (no ``is_summary`` chunk by construction — phase 30)
+    gets exactly one created at position −1 with the new embedding; the
+    content chunks are untouched and the count goes 2 → 3. This is also
+    the recovery path for a phase-30 fail-soft import (document indexed
+    without its summary chunk)."""
+    new = "Talos Kubernetes on 3 nodes with a CNI of choice."
+    _seed_doc(db, summary=None, summary_chunk=False)  # the default kubernetes.md
+    doc_id = _doc_id(db, "kubernetes.md")
+    db.expire_all()
+    before = _chunk_snapshots(db, doc_id)
+    assert len(before) == 2
+    try:
+        fake = FakeEmbedder()
+        monkeypatch.setattr(docs_api, "LLMClient", lambda: fake)
+        r = admin_client.patch(
+            "/api/documents/summary",
+            json={"source": "Homelab", "path": "kubernetes.md", "summary": new},
+        )
+        assert r.status_code == 200, r.text
+        body = r.json()
+        assert body["source"] == "Homelab"
+        assert body["path"] == "kubernetes.md"
+        assert body["summary"] == new
+        assert body["chunks"] == 3  # 2 content + the new is_summary
+        db.expire_all()
+        row = db.get(Document, doc_id)
+        assert row is not None
+        assert row.summary == new
+        after = _chunk_snapshots(db, doc_id)
+        assert len(after) == 3
+        for cid, v in before.items():
+            assert after[cid] == v  # content chunks untouched, byte for byte
+        sc = next(cid for cid in after if cid not in before)
+        pos, content, vec, is_summary = after[sc]
+        assert (pos, is_summary) == (-1, True)
+        assert content == new
+        assert vec is not None and len(vec) == 768
+        assert fake.calls == [[new]]
+    finally:
+        db.execute(text("TRUNCATE chunks, documents"))
+        db.commit()
+
+
+def test_summary_patch_404_unknown_pair(admin_client: TestClient, db: Session) -> None:
+    """Unknown (source, path) pairs — including traversal strings — are
+    just missing rows: 404 ``document not found`` (the same shape as the
+    public GET). A pair that exists under a DIFFERENT source is 404 too."""
+    _seed_yaml_doc(db, summary="old", summary_chunk=True)
+    try:
+        for source, path in (
+            ("Homelab", "nope/missing.md"),
+            ("Deployments", "container_gitlab/gitlab-compose.yaml"),
+            ("Homelab", "../../etc/passwd"),
+        ):
+            r = admin_client.patch(
+                "/api/documents/summary",
+                json={"source": source, "path": path, "summary": "whatever"},
+            )
+            assert r.status_code == 404, (source, path)
+            assert r.json() == {"detail": "document not found"}, (source, path)
+    finally:
+        db.execute(text("TRUNCATE chunks, documents"))
+        db.commit()
+
+
+def test_summary_patch_403_anonymous(client: TestClient, db: Session) -> None:
+    """The edit affordance is admin-only (phase 57, D4 — the viewer stays
+    public): an anonymous PATCH gets 403 ``admin only`` and touches
+    nothing."""
+    old = "GitLab CE runs in a Podman compose stack on the homelab NAS."
+    _seed_yaml_doc(db, summary=old, summary_chunk=True)
+    doc_id = _doc_id(db, "container_gitlab/gitlab-compose.yaml")
+    try:
+        r = client.patch(
+            "/api/documents/summary",
+            json={
+                "source": "Homelab",
+                "path": "container_gitlab/gitlab-compose.yaml",
+                "summary": "not allowed",
+            },
+        )
+        assert r.status_code == 403
+        assert r.json() == {"detail": "admin only"}
+        db.expire_all()
+        row = db.get(Document, doc_id)
+        assert row is not None
+        assert row.summary == old  # untouched
+        assert len(_chunk_snapshots(db, doc_id)) == 3
+    finally:
+        db.execute(text("TRUNCATE chunks, documents"))
+        db.commit()
+
+
+def test_summary_patch_embed_failure_503_db_untouched(
+    admin_client: TestClient, monkeypatch: pytest.MonkeyPatch, db: Session
+) -> None:
+    """Fail-before-write (phase 57 locked decision): a dead embedding
+    endpoint → 503 with a sanitized detail (credentials masked, the
+    reason survives — the ``git_sources.py`` ``ModelUnavailableError``
+    style) and the row + every chunk byte-for-byte as before."""
+    old = "GitLab CE runs in a Podman compose stack on the homelab NAS."
+    _seed_yaml_doc(db, summary=old, summary_chunk=True)
+    doc_id = _doc_id(db, "container_gitlab/gitlab-compose.yaml")
+    db.expire_all()
+    before = _chunk_snapshots(db, doc_id)
+    try:
+        dead = _DeadEmbedder()
+        monkeypatch.setattr(docs_api, "LLMClient", lambda: dead)
+        r = admin_client.patch(
+            "/api/documents/summary",
+            json={
+                "source": "Homelab",
+                "path": "container_gitlab/gitlab-compose.yaml",
+                "summary": "new text",
+            },
+        )
+        assert r.status_code == 503
+        detail = r.json()["detail"]
+        assert "*****@aipi.example.com" in detail  # credentials masked
+        assert "user:secret" not in detail
+        assert "connection refused" in detail  # the reason survives
+        assert dead.calls == [["new text"]]  # the embed was attempted…
+        db.expire_all()
+        row = db.get(Document, doc_id)
+        assert row is not None
+        assert row.summary == old  # …and failed before any mutation
+        assert _chunk_snapshots(db, doc_id) == before  # every row, byte for byte
+    finally:
+        db.execute(text("TRUNCATE chunks, documents"))
+        db.commit()
+
+
 def test_content_200_all_fields(client, db) -> None:
     _seed_doc(db)
     try:
diff --git a/tests/unit/test_summary_edit_ui.py b/tests/unit/test_summary_edit_ui.py
new file mode 100644
index 0000000..1f0de12
--- /dev/null
+++ b/tests/unit/test_summary_edit_ui.py
@@ -0,0 +1,380 @@
+"""Unit: the admin summary-edit affordance in the viewer (phase 57,
+task 02).
+
+The browser behavior itself is E2E-gated by the phase-57 story suite;
+like the other frontend-adjacent unit files (test_save_chat_ui.py
+pattern), this module pins the JS/CSS markers the edit contract depends
+on, so a silent regression is caught without a browser:
+
+* the ``docAdminReady()`` gate — the module-cached /api/whoami promise
+  (header.js's ``fetchIsAdmin``, the SAME single request per page the
+  shared header makes — no second whoami call site in document.js);
+  non-admin / fetch failure → NO button, NO wiring (the public viewer
+  is byte-for-byte the phase-36 section: the bare ``section.append
+  (title, body)`` construction stays first, the admin affordance is a
+  post-render ``.then`` on the gate promise);
+* the editor construction — the header row (``.doc-summary-head`` with
+  the bare h2 + a real ``type="button"`` Edit), the swap-in
+  ``<textarea class="doc-summary-editor">`` prefilled via ``.value``
+  (never innerHTML — XSS contract), Save / Cancel buttons, and the
+  ``role="status"`` ``aria-live="polite"`` live region;
+* the exact PATCH call — ``/api/documents/summary`` with method PATCH
+  and the ``{source, path, summary}`` body (the pair from the doc
+  object — the same values the modal core carries);
+* the outcomes — success re-renders the text node via ``textContent``
+  ("Summary updated."), an empty save that clears removes the panel
+  ("Summary cleared." — the renderer only draws it for non-empty
+  summaries), Cancel restores the text node, and a failure (non-ok OR
+  network) keeps the editor open with the user's text and shows
+  neutral retry copy (phase-55 convention); the double-click guard
+  releases in the ``finally`` — never stale;
+* styles.css — the five new ``.doc-summary-*`` classes (plus the two
+  layout wrappers) on the house dark-tech palette (phase-08 tokens),
+  8rem-min editor, 24px+ edit target, the ``[hidden]`` override,
+  ``:focus-visible`` via the global outline rule, no CDN.
+"""
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
+DOCUMENT_JS = FRONTEND / "assets" / "document.js"
+STYLES_CSS = FRONTEND / "assets" / "styles.css"
+
+
+def _js() -> str:
+    return DOCUMENT_JS.read_text(encoding="utf-8")
+
+
+def _css() -> str:
+    return STYLES_CSS.read_text(encoding="utf-8")
+
+
+def _fn(js: str, name: str) -> str:
+    """The source of a (possibly async, possibly nested) function via
+    balanced-brace counting (works for top-level and the editor's
+    inner helpers alike)."""
+    for prefix in ("async function ", "function "):
+        start = js.find(f"{prefix}{name}(")
+        if start != -1:
+            depth = 0
+            for i in range(js.find("{", start), len(js)):
+                if js[i] == "{":
+                    depth += 1
+                elif js[i] == "}":
+                    depth -= 1
+                    if depth == 0:
+                        return js[start : i + 1]
+            raise AssertionError(f"unbalanced braces in {name}()")
+    raise AssertionError(f"{name}() must exist in document.js")
+
+
+# ---------- the admin gate (D4: the viewer stays public) ----------
+
+
+def test_doc_admin_ready_wraps_the_cached_whoami_promise() -> None:
+    """docAdminReady() exists and resolves the module-cached whoami
+    promise (header.js's fetchIsAdmin — one request per page, shared
+    with initSharedHeader) to a strict boolean: a non-admin OR any
+    fetch failure resolves false (the anonymous viewer)."""
+    js = _js()
+    body = _fn(js, "docAdminReady")
+    assert "await fetchIsAdmin()" in body, (
+        "the gate must reuse the cached whoami promise (no new call site)"
+    )
+    assert "=== true" in body, "a strict boolean — only an authenticated admin"
+    assert "} catch {" in body and "return false" in body, (
+        "any failure resolves false — the anonymous viewer"
+    )
+
+
+def test_no_second_whoami_call_site_in_document_js() -> None:
+    """document.js never fetches /api/whoami itself: header.js's
+    fetchIsAdmin is the SINGLE whoami call site for the whole frontend
+    (the cached promise), so the gate adds no request of its own — and
+    no admin-only network call exists for anonymous visitors (the only
+    admin call, the PATCH, lives inside the wired editor)."""
+    js = _js()
+    assert 'fetch("/api/whoami")' not in js, (
+        "whoami must come from the header.js cached promise"
+    )
+    assert 'from "./header.js"' in js and "fetchIsAdmin" in js
+
+
+def test_gate_runs_after_the_phase36_base_construction() -> None:
+    """The .doc-summary section is built for EVERYONE exactly as phase
+    36 (the anonymous byte-for-byte shape): the base construction
+    (className, the bare h2 label, the .doc-summary-text node, the
+    append) precedes the gate call, and the admin wiring runs ONLY in
+    the gate's success branch (``if (admin) wireSummaryEdit(...)``)."""
+    js = _js()
+    base = js.find('section.className = "doc-summary"')
+    label = js.find('title.textContent = "Summary"')
+    text_node = js.find('body.className = "doc-summary-text"')
+    append = js.find("section.append(title, body)")
+    mount = js.find("contentEl.appendChild(section)")
+    gate = js.find("void docAdminReady().then(")
+    wiring = js.find("if (admin) wireSummaryEdit(section, doc);")
+    assert 0 < base < label < text_node < append < mount < gate < wiring, (
+        "phase-36 base construction first; the admin affordance is a "
+        "post-render gate branch (anonymous DOM is never touched)"
+    )
+    assert "wireSummaryEdit(section, doc)" in js[gate:]
+
+
+# ---------- the editor construction ----------
+
+
+def test_edit_button_is_a_real_button_in_the_header_row() -> None:
+    """The Edit affordance: a real ``type="button"`` with the visible
+    text "Edit" and the .doc-summary-edit class, added to a
+    .doc-summary-head row that keeps the bare h2 label (label left,
+    button right — the anonymous section keeps its bare h2)."""
+    body = _fn(_js(), "wireSummaryEdit")
+    assert 'editBtn.type = "button"' in body
+    assert 'editBtn.className = "doc-summary-edit"' in body
+    assert 'editBtn.textContent = "Edit"' in body
+    assert 'head.className = "doc-summary-head"' in body
+    assert "head.append(title, editBtn)" in body
+    # The header row REPLACES the bare h2 as the section's first child.
+    assert "section.replaceChildren(head, body)" in body
+
+
+def test_editor_swap_builds_textarea_save_cancel_and_live_region() -> None:
+    """Edit swaps the .doc-summary-text node for the inline editor:
+    a <textarea class="doc-summary-editor"> prefilled via ``.value``
+    (NEVER innerHTML — the XSS contract), Save / Cancel real
+    type=buttons, and a <p class="doc-summary-status" role="status"
+    aria-live="polite"> live region. The Edit button hides while the
+    editor is open (no re-open mid-edit) and the textarea gets focus.
+    The ENTIRE wiring is textContent/.value-only — no innerHTML
+    anywhere (summary text is user-storable)."""
+    js = _js()
+    body = _fn(js, "wireSummaryEdit")
+    assert 'editor.className = "doc-summary-editor"' in body
+    assert (
+        'editor.value = typeof doc.summary === "string" ? doc.summary : ""' in body
+    ), "prefill via .value — value, not innerHTML"
+    assert 'saveBtn.type = "button"' in body
+    assert 'saveBtn.className = "doc-summary-save"' in body
+    assert 'saveBtn.textContent = "Save"' in body
+    assert 'cancelBtn.type = "button"' in body
+    assert 'cancelBtn.className = "doc-summary-cancel"' in body
+    assert 'cancelBtn.textContent = "Cancel"' in body
+    assert 'status.className = "doc-summary-status"' in body
+    assert 'status.setAttribute("role", "status")' in body
+    assert 'status.setAttribute("aria-live", "polite")' in body
+    # The swap: text node out, editor parts in, focus in.
+    assert "section.replaceChildren(head, editor, actions, status)" in body
+    assert "editor.focus()" in body
+    hide = body.find("editBtn.hidden = true")
+    swap = body.find("section.replaceChildren(head, editor, actions, status)")
+    focus = body.find("editor.focus()")
+    assert -1 < hide < swap < focus, "hide Edit → swap → focus the textarea"
+    # The bindings.
+    assert 'editBtn.addEventListener("click", openEditor)' in body
+    assert 'cancelBtn.addEventListener("click", () => closeEditor(""))' in body
+    # XSS contract: the whole affordance is textContent/.value only
+    # (comments stripped — the word may appear in a note, never in code).
+    code = re.sub(r"//.*?$|/\*.*?\*/", "", body, flags=re.S | re.M)
+    assert "innerHTML" not in code, "XSS contract: no innerHTML in the wiring"
+
+
+# ---------- the PATCH round-trip ----------
+
+
+def test_save_patches_the_exact_endpoint_with_the_doc_pair() -> None:
+    """Save → PATCH /api/documents/summary (the phase-57 admin
+    endpoint) with the EXACT body shape {source, path, summary} — the
+    pair from the doc object (the same values the modal core carries),
+    JSON content type. This is the ONLY admin-only call in document.js
+    (exactly one call site, inside the wired editor — anonymous
+    visitors never have it)."""
+    js = _js()
+    assert js.count('fetch("/api/documents/summary"') == 1, (
+        "exactly one PATCH call site (inside wireSummaryEdit)"
+    )
+    body = _fn(js, "wireSummaryEdit")
+    fetch_i = body.find('fetch("/api/documents/summary"')
+    assert fetch_i != -1, "the PATCH must live in the wired editor"
+    assert 'method: "PATCH"' in body[fetch_i:]
+    assert '"Content-Type": "application/json"' in body[fetch_i:]
+    assert (
+        "JSON.stringify({ source: doc.source, path: doc.path, summary: value })"
+        in body
+    ), "the exact body shape: {source, path, summary}"
+
+
+def test_save_success_rerenders_text_node_and_announces() -> None:
+    """A 200 update syncs the doc object (a later re-open prefills the
+    CURRENT summary), announces "Summary updated." through
+    closeEditor — which re-renders the text node via textContent ONLY
+    (XSS contract) from the doc object."""
+    body = _fn(_js(), "wireSummaryEdit")
+    ok_i = body.find("if (!res.ok)")
+    json_i = body.find("await res.json()")
+    null_i = body.find("if (data.summary === null)")
+    sync_i = body.find("doc.summary = data.summary")
+    announce_i = body.find('closeEditor("Summary updated.")')
+    assert -1 < ok_i < json_i < null_i < sync_i < announce_i, (
+        "non-ok checked first → JSON → clear branch → doc sync → announce"
+    )
+    close = _fn(body, "closeEditor")
+    assert "body.textContent = doc.summary" in close, (
+        "the display state re-renders the text node from the doc object"
+    )
+
+
+def test_empty_save_clears_and_removes_the_panel() -> None:
+    """An empty save that clears (response summary === null, D4) syncs
+    the doc object, announces "Summary cleared." in the live region,
+    and removes the panel a short beat LATER (setTimeout — the
+    confirmation stays readable before the panel leaves the DOM; the
+    renderer only draws it for non-empty summaries). Failures keep the
+    panel (their slices carry no removal)."""
+    body = _fn(_js(), "wireSummaryEdit")
+    null_i = body.find("if (data.summary === null)")
+    sync_i = body.find("doc.summary = null")
+    announce_i = body.find('status.textContent = "Summary cleared."')
+    remove_i = body.find("setTimeout(() => section.remove(), 2000)")
+    assert -1 < null_i < sync_i < announce_i < remove_i, (
+        "the null branch: sync → announce → delayed removal"
+    )
+    # Exactly two removals in the whole affordance, both tied to a
+    # CLEARED state (the clear branch + the closeEditor empty guard —
+    # no failure path removes the panel).
+    assert body.count("section.remove()") == 2
+
+
+def test_cancel_restores_the_text_node() -> None:
+    """Cancel restores the display state: the .doc-summary-text node
+    back in the section, re-rendered from the doc object (the CURRENT
+    stored summary — the node was never mutated, only swapped out),
+    the (empty) live region kept, and the Edit button un-hidden +
+    re-focused (focus returns to the opener). A summary that is GONE
+    (a clear landed while the editor was open — Cancel right after a
+    successful empty save) never renders an empty panel: the guard
+    drops the panel instead."""
+    body = _fn(_js(), "wireSummaryEdit")
+    close = _fn(body, "closeEditor")
+    assert 'status.textContent = message' in close
+    assert "editBtn.hidden = false" in close
+    guard = 'typeof doc.summary !== "string" || doc.summary.trim() === ""'
+    guard_i = close.find(guard)
+    remove_i = close.find("section.remove()")
+    sync_i = close.find("body.textContent = doc.summary")
+    restore_i = close.find("section.replaceChildren(head, body, status)")
+    focus_i = close.find("editBtn.focus()")
+    assert -1 < guard_i < remove_i < sync_i < restore_i < focus_i, (
+        "empty guard first; otherwise re-render → restore → focus"
+    )
+    assert 'cancelBtn.addEventListener("click", () => closeEditor(""))' in body
+
+
+def test_failure_keeps_the_editor_with_neutral_copy() -> None:
+    """A failed Save (non-ok HTTP OR network) keeps the editor open
+    with the user's text (no swap back, no panel removal) and shows
+    neutral retry copy (phase-55 convention — no sign-in wording):
+    "…try again." for a non-ok response, "…is the app reachable?" for
+    the network path."""
+    body = _fn(_js(), "wireSummaryEdit")
+    nonok = body.find("if (!res.ok)")
+    neutral = body.find("Couldn't update the summary — try again.")
+    assert -1 < nonok < neutral, "the non-ok branch lands on the neutral copy"
+    catch_i = body.find("} catch {")
+    reachable = body.find("Couldn't update the summary — is the app reachable?")
+    assert -1 < catch_i < reachable, "the network path carries the reachable? copy"
+    assert "signed in" not in body, "no sign-in wording (neutral retry copy)"
+    # The two FAILURE branches (the non-ok early return and the network
+    # catch) never restore or remove — the editor stays open with the
+    # user's text (only the clear branch removes the panel).
+    nonok_slice = body[nonok:body.find("await res.json()")]
+    assert "section.remove()" not in nonok_slice
+    assert "closeEditor" not in nonok_slice
+    catch_slice = body[catch_i:body.find("finally")]
+    assert "section.remove()" not in catch_slice
+    assert "closeEditor" not in catch_slice
+
+
+def test_save_double_click_guard_releases_in_finally() -> None:
+    """One PATCH at a time: Save disables itself BEFORE the fetch and
+    re-enables in the ``finally`` (every outcome — success, clear,
+    non-ok, network — never leaves a stale disabled button, PLAN §7.4)."""
+    body = _fn(_js(), "wireSummaryEdit")
+    disable_i = body.find("saveBtn.disabled = true")
+    fetch_i = body.find('fetch("/api/documents/summary"')
+    finally_i = body.find("finally")
+    enable_i = body.find("saveBtn.disabled = false")
+    assert -1 < disable_i < fetch_i < finally_i < enable_i, (
+        "disable before the fetch; re-enable in the finally"
+    )
+    assert body.count("saveBtn.disabled = true") == 1
+    assert body.count("saveBtn.disabled = false") == 1
+
+
+# ---------- styles.css ----------
+
+
+def test_new_summary_edit_classes_present() -> None:
+    """styles.css carries the five task-named .doc-summary-* classes
+    (plus the two layout wrappers the wiring emits) — the house
+    dark-tech palette (phase-08 tokens), system fonts, no CDN."""
+    css = _css()
+    for cls in (
+        ".doc-summary-edit",
+        ".doc-summary-editor",
+        ".doc-summary-save",
+        ".doc-summary-cancel",
+        ".doc-summary-status",
+        ".doc-summary-head",
+        ".doc-summary-actions",
+    ):
+        assert f"{cls} " in css or f"{cls}." in css or f"{cls}[" in css, (
+            f"styles.css must style {cls}"
+        )
+    assert "url(http" not in css and "@import url(" not in css, (
+        "no CDN (AGENTS.md rule 6)"
+    )
+
+
+def test_summary_edit_css_targets_and_palette() -> None:
+    """The house AA palette on the edit affordance: the edit target is
+    24px+ with a 3px global-outline focus (the global :focus-visible
+    rule — no local override needed); the editor is a full-width block
+    textarea with the 8rem min-height; the save pill is the solid
+    brand family (--bg on --brand = 5.2:1, AA, borderless); the ghost
+    buttons ride the ink-soft 5.1:1-on-surface pair; the status line
+    is ink-soft (AA). The [hidden] override must beat the edit
+    button's display rule (the editor hides Edit while open)."""
+    css = _css()
+    edit = css[css.find(".doc-summary-edit {") :]
+    edit = edit[: edit.find("\n}")]
+    assert "min-height: 24px" in edit, "the 24px+ edit target (task 02)"
+    assert "var(--line)" in edit and "var(--ink-soft)" in edit
+    hidden = css.find(".doc-summary-edit[hidden]")
+    assert hidden != -1 and "display: none" in css[hidden : hidden + 80], (
+        "the hidden attr must beat the base display rule"
+    )
+    editor = css[css.find(".doc-summary-editor {") :]
+    editor = editor[: editor.find("\n}")]
+    for prop in (
+        "display: block",
+        "width: 100%",
+        "min-height: 8rem",
+        "resize: vertical",
+        "var(--bg)",
+        "var(--ink)",
+    ):
+        assert prop in editor, f".doc-summary-editor must keep {prop}"
+    save = css[css.find(".doc-summary-save {") :]
+    save = save[: save.find("\n}")]
+    assert "background: var(--brand)" in save and "color: var(--bg)" in save
+    assert "border: 0" in save, "the solid brand pill family (Save/Share)"
+    status = css[css.find(".doc-summary-status {") :]
+    status = status[: status.find("\n}")]
+    assert "var(--ink-soft)" in status, "AA status copy on --surface (5.1:1)"
+    # :focus-visible via the GLOBAL 3px outline rule (no local
+    # suppression anywhere for these controls).
+    assert ":focus-visible {" in css
+    assert "outline: 3px solid var(--brand)" in css