feat(booth): render .md/.txt/.log inline in the gallery, collapsible + closable

Docs used to render as a clumsy link that navigated to a separate page. They
now render in place: build_gallery pre-renders each doc (markdown -> HTML,
plain text raw) and the gallery shows it inside a native <details open>
disclosure that spans the full grid width so prose has a readable measure.

The doc bar carries: a collapse chevron (the whole <details> summary toggles,
works with JS off), a full-page link (still reaches the standalone viewer), a
download link, and a session-close ✕. The ✕ needed stopPropagation +
preventDefault because it lives inside <summary> — otherwise its click would
toggle the disclosure instead of hiding the item. Close is JS (progressive
enhancement); collapse is native.

Two design points:
- Plain text is returned RAW from build_gallery and escaped by the template
  inside <pre>. Pre-escaping in Python plus Jinja autoescape would
  double-encode angle brackets; a test pins the single-escape.
- Inlining is bounded by DOC_MAX_BYTES. A doc over the limit keeps the old
  link-out behaviour rather than being rendered into every index load; a test
  covers the fallback.

The shared .markdown-body / .textview typography moved from doc.html's scoped
<style> into base.html so the inline body and the full-page view render
identically; doc.html keeps only its page-layout wrapper.

Updated the pre-existing test_gallery_links_docs_to_view: it asserted the old
link-out behaviour the operator asked to change, so it now asserts the inline
render plus the surviving full-page and download affordances. 61 pass.
Verified live: markdown renders with headings/table/blockquote/code, txt
preserves whitespace and single-escapes, collapse and ✕-close both work.

services/booth/tests/test_booth.py

@@ -105,6 +105,89 @@ def test_build_gallery_folds_caption_sidecars(tmp_path):
     assert "loose.txt" in by_name  # a caption with nothing to caption stays visible
 
 
+# ---- inline doc rendering ---------------------------------------------------
+#
+# .md / .txt / .log docs render INLINE in the gallery (collapsible), not as a
+# clumsy link to a separate page. build_gallery pre-renders the content so the
+# template stays logicless.
+
+
+def test_build_gallery_prerenders_markdown_inline(tmp_path):
+    booth = tmp_path / "b"
+    booth.mkdir()
+    (booth / "report.md").write_text("# Title\n\nsome **bold** text\n")
+
+    it = next(i for i in build_gallery(booth) if i["name"] == "report.md")
+
+    assert it["doc"] == "markdown"
+    assert it["rendered_html"] is True
+    assert "<h1>Title</h1>" in it["rendered"]
+    assert "<strong>bold</strong>" in it["rendered"]
+
+
+def test_build_gallery_prerenders_text_as_raw(tmp_path):
+    booth = tmp_path / "b"
+    booth.mkdir()
+    (booth / "notes.txt").write_text("plain <not html> line")
+
+    it = next(i for i in build_gallery(booth) if i["name"] == "notes.txt")
+
+    assert it["doc"] == "text"
+    assert it["rendered_html"] is False
+    # Raw text is NOT pre-escaped here — the template escapes it inside <pre>.
+    # Pre-escaping plus template autoescape would double-encode the angle brackets.
+    assert it["rendered"] == "plain <not html> line"
+
+
+def test_build_gallery_oversize_doc_is_not_inlined(tmp_path):
+    booth = tmp_path / "b"
+    booth.mkdir()
+    big = "x" * (2 * 1024 * 1024 + 10)  # over DOC_MAX_BYTES
+    (booth / "huge.log").write_text(big)
+
+    it = next(i for i in build_gallery(booth) if i["name"] == "huge.log")
+
+    assert it["doc"] == "text"
+    assert it["rendered"] is None  # too big to inline; template falls back to a link
+
+
+def test_non_doc_item_has_no_rendered_field(tmp_path):
+    booth = tmp_path / "b"
+    _touch(booth / "shot.png")
+
+    it = next(i for i in build_gallery(booth) if i["name"] == "shot.png")
+
+    assert it["doc"] is None
+    assert it["rendered"] is None
+
+
+def test_booth_page_renders_markdown_inline_collapsible(client):
+    c, data = client
+    (data / "run1").mkdir()
+    (data / "run1" / "brief.md").write_text("# Heading\n\nbody line\n")
+
+    html = c.get("/b/run1/").text
+
+    # rendered inline, inside a native <details> disclosure — no navigation
+    assert "<details" in html
+    assert "<h1>Heading</h1>" in html
+    # and the raw-file link is still available for download / full view
+    assert "brief.md" in html
+
+
+def test_booth_page_inlines_txt_without_double_escaping(client):
+    c, data = client
+    (data / "run1").mkdir()
+    (data / "run1" / "log.txt").write_text("value <x> & <y>")
+
+    html = c.get("/b/run1/").text
+
+    # exactly one level of HTML-escaping (template autoescape inside <pre>),
+    # not the double-encoding that pre-escaping in Python would produce
+    assert "value &lt;x&gt; &amp; &lt;y&gt;" in html
+    assert "&amp;lt;" not in html
+
+
 # ---- HTTP surface -----------------------------------------------------------
 
 
@@ -487,15 +570,20 @@ def test_view_text_shows_preformatted(client):
     assert "attachment" not in r.headers.get("content-disposition", "")
 
 
-def test_gallery_links_docs_to_view(client):
+def test_gallery_inlines_docs_with_fullpage_and_download_affordances(client):
+    # Docs now render INLINE in the gallery (see the inline-doc tests above),
+    # not as a link. The full-page viewer stays reachable via the ⤢ affordance,
+    # and the raw file via a download link — but the doc content itself is on
+    # the page, not behind a click.
     c, data = client
     d = data / "run1"; d.mkdir()
     (d / "readme.md").write_text("# hi")
     (d / "notes.txt").write_text("hello")   # loose txt (no media partner) -> own item
-    page = c.get("/b/run1/")
-    assert "view?f=readme.md" in page.text   # md -> viewer
-    assert "view?f=notes.txt" in page.text   # txt -> viewer
-    assert 'href="readme.md" download' not in page.text   # not a forced download
+    page = c.get("/b/run1/").text
+    assert "<h1>hi</h1>" in page              # md rendered inline
+    assert "hello" in page                    # txt shown inline
+    assert "view?f=readme.md" in page         # full-page viewer still linked (⤢)
+    assert 'href="readme.md" download' in page  # download affordance present
 
 
 # ---- image viewer prev/next nav ---------------------------------------------