diff --git a/docs/architecture-undigg.md b/docs/architecture-undigg.md
index d7f198a..f3bda6b 100644
--- a/docs/architecture-undigg.md
+++ b/docs/architecture-undigg.md
@@ -3,132 +3,211 @@
 Document-first platform: every namespace is a book, every thread is a chapter,
 every reply is a section. Pandoc renders 67 output formats.
 
-## Data Flow
+## Data Flow — Write Path
 
+```dot
+digraph write_path {
+    rankdir=LR
+    node [shape=box, style=rounded, fontname="sans-serif"]
+    edge [fontname="sans-serif", fontsize=10]
+
+    input [label="User Input\n(md, html, rst,\nmediawiki, latex,\ntextile, org, ...)", shape=note]
+    source_fmt [label="source_format\ndetection", shape=diamond]
+    pandoc_html [label="pandoc\nconvert to html5"]
+    pandoc_roundtrip [label="pandoc\nhtml → markdown\n(round-trip clean)"]
+    bleach [label="bleach\nsanitize"]
+    data [label="Node.data\n(raw source)", shape=cylinder]
+    data_html [label="Node.data_html\n(rendered)", shape=cylinder]
+    source_col [label="Node.source_format", shape=cylinder]
+
+    input -> source_fmt
+    source_fmt -> pandoc_html [label="rst, mediawiki,\nlatex, etc."]
+    source_fmt -> pandoc_roundtrip [label="html input"]
+    source_fmt -> data [label="markdown\n(direct)"]
+    pandoc_roundtrip -> data [label="cleaned md"]
+    pandoc_html -> bleach
+    bleach -> data_html
+    input -> source_col [style=dashed, label="store format"]
+    data -> data_html [label="markdown_to_html\n(for md input)", style=dashed]
+}
 ```
-                          ┌─────────────────────────────────────────────┐
-                          │              Write Path                     │
-                          │                                             │
-  User Input              │  source_format     pandoc         bleach    │
-  (md/html/rst/           │  ─────────────►  convert to  ──► sanitize  │
-   mediawiki/latex/       │                   html5          pipeline   │
-   textile/org/...)       │                     │                │      │
-                          │                     │                ▼      │
-                          │                     │           data_html   │
-                          │                     │          (rendered)   │
-                          │                     │                       │
-                          │  html input:        │                       │
-                          │  pandoc html→md     │                       │
-                          │  (round-trip clean) │                       │
-                          │         │           │                       │
-                          │         ▼           │                       │
-                          │     data (raw)      │                       │
-                          │   + source_format   │                       │
-                          └─────────────────────────────────────────────┘
 
-                          ┌─────────────────────────────────────────────┐
-                          │              Read / Export Path              │
-                          │                                             │
-  Node tree               │  tree-to-markdown    pandoc                 │
-  (adjacency list)  ────► │  renderer         ──► convert to  ────►  output
-                          │                      target format          │
-                          │                                             │
-                          │  Hierarchy:                                 │
-                          │    # Thread Title     (h1)                  │
-                          │    ## Author Name     (h2, per reply)       │
-                          │    ### Author Name    (h3, nested reply)    │
-                          │    ...depth maps to heading level           │
-                          └─────────────────────────────────────────────┘
+## Data Flow — Read / Export Path
+
+```dot
+digraph read_path {
+    rankdir=LR
+    node [shape=box, style=rounded, fontname="sans-serif"]
+    edge [fontname="sans-serif", fontsize=10]
+
+    tree [label="Node tree\n(adjacency list)", shape=cylinder]
+    renderer [label="tree-to-markdown\nrenderer"]
+    pandoc [label="pandoc\nconvert to\ntarget format"]
+    output [label="Output\n(pdf, epub, docx,\nhtml, rst, ...)", shape=note]
+
+    tree -> renderer
+    renderer -> pandoc [label="markdown\ndocument"]
+    pandoc -> output
+
+    subgraph cluster_heading_map {
+        label="Heading depth mapping"
+        style=dashed
+        fontname="sans-serif"
+        h1 [label="# Thread Title (h1)", shape=plaintext]
+        h2 [label="## Author Name (h2, reply)", shape=plaintext]
+        h3 [label="### Author Name (h3, nested)", shape=plaintext]
+    }
+}
 ```
 
 ## Export Hierarchy
 
-```
-  Namespace (book)
-  GET /api/v1/export/namespace/{name}.{fmt}
-  │
-  ├── Root Node A (chapter)           ← default export
-  │   GET /api/v1/export/threads/{id}.{fmt}
-  │   │
-  │   ├── Reply 1 (section)           ← on-demand
-  │   │   GET /api/v1/export/nodes/{id}.{fmt}
-  │   │   │
-  │   │   └── Reply 1.1 (subsection)  ← on-demand
-  │   │
-  │   └── Reply 2 (section)           ← on-demand
-  │
-  └── Root Node B (chapter)           ← default export
-      GET /api/v1/export/threads/{id}.{fmt}
+```dot
+digraph export_hierarchy {
+    rankdir=TB
+    node [shape=box, style=rounded, fontname="sans-serif"]
+    edge [fontname="sans-serif", fontsize=10]
+
+    ns [label="Namespace (book)\n/export/namespace/{name}.{fmt}"]
+    rootA [label="Root Node A (chapter)\n/export/threads/{id}.{fmt}"]
+    rootB [label="Root Node B (chapter)\n/export/threads/{id}.{fmt}"]
+    reply1 [label="Reply 1 (section)\n/export/nodes/{id}.{fmt}"]
+    reply2 [label="Reply 2 (section)\n/export/nodes/{id}.{fmt}"]
+    reply1_1 [label="Reply 1.1 (subsection)\n/export/nodes/{id}.{fmt}"]
+
+    ns -> rootA [label="default"]
+    ns -> rootB [label="default"]
+    rootA -> reply1 [label="on-demand"]
+    rootA -> reply2 [label="on-demand"]
+    reply1 -> reply1_1 [label="on-demand"]
+}
 ```
 
-**67 output formats** including: markdown, html5, pdf, epub, docx, odt, rst,
+67 output formats including: markdown, html5, pdf, epub, docx, odt, rst,
 latex, mediawiki, man, plain, rtf, asciidoc, textile, org, json, and more.
 
 ## Wiki Mode
 
-```
-  ┌──────────────┐      wiki_edit()      ┌──────────────┐
-  │              │  ──────────────────►  │  rb_revision  │
-  │   rb_node    │                       │               │
-  │              │  1. snapshot current   │  id           │
-  │  id          │     data → revision   │  node_id (FK) │
-  │  data        │  2. increment rev#    │  user_id (FK) │
-  │  data_html   │  3. overwrite node    │  data          │
-  │  source_fmt  │     with new content  │  source_format │
-  │              │                       │  revision_number│
-  └──────────────┘                       │  created       │
-        │                                └──────────────┘
-        │
-        ▼
-  can_wiki_edit(node, user)?
-  ├── user.authenticated?           → required
-  ├── namespace.can_alter_node()?   → owner/moderator always yes
-  └── namespace.wiki && node.is_root? → wiki mode for root nodes
+```dot
+digraph wiki_mode {
+    rankdir=TB
+    node [shape=record, fontname="sans-serif"]
+    edge [fontname="sans-serif", fontsize=10]
+
+    rb_node [label="{rb_node|id\ldata\ldata_html\lsource_format\l}"]
+    rb_revision [label="{rb_revision|id\lnode_id (FK)\luser_id (FK)\ldata\lsource_format\lrevision_number\lcreated\l}"]
+    wiki_edit [label="wiki_edit()", shape=ellipse]
+    check [label="can_wiki_edit(node, user)?", shape=diamond]
+
+    rb_node -> wiki_edit [label="called on node"]
+    wiki_edit -> rb_revision [label="1. snapshot\ncurrent data"]
+    wiki_edit -> rb_node [label="3. overwrite\nwith new content", style=dashed]
+
+    check -> wiki_edit [label="allowed"]
+
+    subgraph cluster_perms {
+        label="Permission checks"
+        style=dashed
+        fontname="sans-serif"
+        node [shape=plaintext]
+        p1 [label="user.authenticated → required"]
+        p2 [label="namespace.can_alter_node() → owner/moderator always yes"]
+        p3 [label="namespace.wiki && node.is_root → wiki mode for root nodes"]
+    }
+
+    check -> p1 [style=invis]
+}
 ```
 
 ## Auto-Generated Themes
 
-```
-  namespace_name
-       │
-       ▼
-  SHA-256 hash
-       │
-       ├── bits[0:8]   → hue (0-360)
-       ├── bits[8:40]  → 8 seed values
-       │
-       ▼
-  HSL color palette
-       │
-       ├── Light mode (:root, .theme-light)
-       │   --rb-bg, --rb-text, --rb-link, --rb-accent, --rb-border, ...
-       │
-       └── Dark mode (@media prefers-color-scheme: dark, .theme-dark)
-           --rb-bg, --rb-text, --rb-link, --rb-accent, --rb-border, ...
+```dot
+digraph themes {
+    rankdir=TB
+    node [shape=box, style=rounded, fontname="sans-serif"]
+    edge [fontname="sans-serif", fontsize=10]
 
-  Deterministic: same namespace → same theme, always.
-  Served at: GET /api/v1/themes/{namespace}/css  (1-day cache)
-  Preview:   GET /api/v1/themes/{namespace}/preview  (JSON palette)
+    name [label="namespace_name", shape=plaintext]
+    sha [label="SHA-256 hash"]
+    hue [label="hue (0-360)\nbits[0:8]"]
+    seeds [label="8 seed values\nbits[8:40]"]
+    palette [label="HSL color palette"]
+
+    light [label="Light mode\n:root, .theme-light\n--rb-bg, --rb-text,\n--rb-link, --rb-accent,\n--rb-border, ...", shape=note]
+    dark [label="Dark mode\n@media prefers-color-scheme: dark\n.theme-dark\n--rb-bg, --rb-text,\n--rb-link, --rb-accent,\n--rb-border, ...", shape=note]
+
+    css [label="GET /api/v1/themes/{ns}/css\n(1-day cache)", shape=component]
+    preview [label="GET /api/v1/themes/{ns}/preview\n(JSON palette)", shape=component]
+
+    name -> sha
+    sha -> hue
+    sha -> seeds
+    hue -> palette
+    seeds -> palette
+    palette -> light
+    palette -> dark
+    light -> css
+    dark -> css
+    palette -> preview
+}
 ```
 
+Deterministic: same namespace name always produces the same theme.
+
 ## Module Map
 
-```
-  remarkbox/
-  ├── lib/
-  │   ├── pandoc.py              ← subprocess wrapper, tree renderer
-  │   └── theme_generator.py     ← deterministic CSS from namespace name
-  ├── api/
-  │   ├── export.py              ← /export/ endpoints (namespace, thread, node)
-  │   ├── wiki.py                ← /wiki-edit, /revisions endpoints
-  │   ├── themes.py              ← /themes/ endpoints (css, preview)
-  │   ├── views.py               ← modified: source_format on create/reply/edit
-  │   └── serializers.py         ← modified: source_format in node JSON
-  ├── models/
-  │   ├── node.py                ← modified: source_format column, set_data(), wiki_edit()
-  │   ├── namespace.py           ← modified: can_wiki_edit()
-  │   └── revision.py            ← new: Revision model
-  └── scripts/alembic/versions/
-      ├── d47dc908d2ea_...       ← add source_format to rb_node
-      └── 8e3c406e4049_...       ← create rb_revision table
+```dot
+digraph modules {
+    rankdir=TB
+    node [shape=box, fontname="monospace", fontsize=10]
+    edge [fontname="sans-serif", fontsize=9]
+    compound=true
+
+    subgraph cluster_lib {
+        label="remarkbox/lib/"
+        style=rounded
+        fontname="sans-serif"
+        pandoc_py [label="pandoc.py\nsubprocess wrapper\ntree renderer"]
+        theme_gen [label="theme_generator.py\ndeterministic CSS"]
+    }
+
+    subgraph cluster_api {
+        label="remarkbox/api/"
+        style=rounded
+        fontname="sans-serif"
+        export_py [label="export.py\n/export/ endpoints"]
+        wiki_py [label="wiki.py\n/wiki-edit, /revisions"]
+        themes_py [label="themes.py\n/themes/ endpoints"]
+        views_py [label="views.py\nsource_format on\ncreate/reply/edit"]
+        serial_py [label="serializers.py\nsource_format in JSON"]
+    }
+
+    subgraph cluster_models {
+        label="remarkbox/models/"
+        style=rounded
+        fontname="sans-serif"
+        node_py [label="node.py\nsource_format column\nset_data(), wiki_edit()"]
+        ns_py [label="namespace.py\ncan_wiki_edit()"]
+        rev_py [label="revision.py\nRevision model"]
+    }
+
+    subgraph cluster_migrations {
+        label="remarkbox/scripts/alembic/versions/"
+        style=rounded
+        fontname="sans-serif"
+        mig1 [label="d47dc908d2ea\nadd source_format"]
+        mig2 [label="8e3c406e4049\ncreate rb_revision"]
+    }
+
+    export_py -> pandoc_py
+    themes_py -> theme_gen
+    wiki_py -> rev_py
+    wiki_py -> node_py
+    views_py -> node_py
+    export_py -> node_py
+    export_py -> ns_py
+    node_py -> pandoc_py [style=dashed, label="non-md formats"]
+    mig1 -> node_py [style=dotted]
+    mig2 -> rev_py [style=dotted]
+}
 ```
diff --git a/docs/tickets/15.md b/docs/tickets/15.md
index 0599ff4..9a11629 100644
--- a/docs/tickets/15.md
+++ b/docs/tickets/15.md
@@ -13,10 +13,24 @@ Wiki mode lets anyone edit root topics with revision tracking.
 
 ## Architecture
 
-```
-Namespace (book)           → pandoc → all formats (default)
-  └── Root Node (chapter)  → pandoc → all formats (default)
-        └── Reply (section) → pandoc → on-demand only
+```dot
+digraph export_hierarchy {
+    rankdir=LR
+    node [shape=box, style=rounded, fontname="sans-serif"]
+
+    namespace [label="Namespace\n(book)"]
+    root [label="Root Node\n(chapter)"]
+    reply [label="Reply\n(section)"]
+    pandoc [label="pandoc", shape=ellipse]
+    formats [label="67 output\nformats", shape=note]
+
+    namespace -> root [label="contains"]
+    root -> reply [label="contains"]
+    namespace -> pandoc [label="default"]
+    root -> pandoc [label="default"]
+    reply -> pandoc [label="on-demand"]
+    pandoc -> formats
+}
 ```
 
 ### Data model changes