feat: Improved opengraph defaults.

AGENTS.md

@@ -5,63 +5,119 @@ Thor is a static site generator written in [Odin](https://odin-lang.org), replac
 ## Architecture
 
 ```
-thor.json          ← site config (title, base_url, author, params)
+thor.json          ← site config (title, base_url, author, params, modules)
 content/           ← markdown and HTML content files
-layouts/           ← Mustache templates + partials (including icons)
+layouts/           ← Mustache templates + partials (user overrides)
-assets/            ← CSS (Tufte-based), JS, fonts, images — copied/processed to public/
+assets/            ← CSS (Tufte-based), JS, fonts, images
+thor/defaults/     ← bundled default templates (embedded via #directory)
 public/            ← build output (generated)
 ```
 
-### Source files
+### Package structure
+
+```
+thor/
+├── treesitter/         # FFI types + grammar management (standalone package)
+├── markdown/           # Content transformation pipeline (imports ../treesitter)
+├── mustache/           # Template engine with lambdas + pipe filters
+├── content.odin        # Page struct, scan_content, load_page
+├── render.odin         # Template rendering, data structs, RSS, sitemap
+├── site.odin           # Config (Flags, Config_File, Site), init_site
+├── minify.odin         # HTML/CSS minification (imports treesitter)
+├── feed.odin           # RSS + sitemap generation
+├── vfs.odin            # Union file system (defaults → modules → site)
+├── assets.odin         # VFS-based asset copying
+├── opengraph.odin      # Open_Graph struct + og_init/og_for_page
+├── frontmatter.odin    # JSON frontmatter parser
+├── defaults.odin       # DEFAULTS_PATH constant (#directory)
+├── main.odin           # Entry point
+└── defaults/layouts/   # Bundled default templates
+```
+
+### Source files (main package)
 
 | File | Responsibility |
 |---|---|
-| `main.odin` | Entry point. Sets `context.logger`, calls `init_site`, `walk_content`, `render_site`. Optional Spall profiling via `SPALL` config flag. |
+| `main.odin` | Entry point. Sets `context.logger`, calls `init_site`, `build_vfs`, `site_load_content`, `render_site`. Optional Spall profiling via `SPALL` config flag. |
-| `site.odin` | `Flags` (CLI args), `Config_File` (from `thor.json`), `Site` (runtime state + arena), `Feature` + `Markdown_Extension` bit_set enums, `DEFAULT_MARKDOWN_EXTENSIONS`, 5-step `init_site` (defaults → flags → config → apply config → apply flags), `load_config_file`, `apply_config`, `apply_cli_flags`, `parse_extension_list`, `find_config` |
+| `site.odin` | `Flags` (CLI), `Config_File` (thor.json), `Site` (runtime state + arena + VFS + pages + modules). `Feature` enum. 5-step `init_site`. Imports `md "markdown"` for `Extension` enum. |
-| `frontmatter.odin` | JSON frontmatter parser (`{ }` delimited) |
+| `content.odin` | `Page` struct, `scan_content` (section-aware walk that handles leaf bundles), `load_page`, `infer_layout`. Calls `md.process()` for the markdown pipeline. |
-| `content.odin` | `Page` struct, content walker, page loader, cmark integration, full markdown pipeline, `copy_assets_dir` (recursive copy with CSS minification) |
+| `render.odin` | Template rendering: `render_site`, `render_page_html`, `render_home_html`, `render_section`. Data structs (`Base_Data`, `Page_Data`, `Home_Data`, `Section_Data`). VFS-based template loading with fallback chain (`get_template`). |
-| `footnotes.odin` | Note definition stripping (pre-cmark) + sidenote/marginnote injection (post-cmark) |
+| `minify.odin` | HTML/CSS minification via tree-sitter. Imports `ts "treesitter"`. |
-| `alerts.odin` | GitHub alert post-processor (`> [!CAUTION]` → styled blockquote) |
+| `feed.odin` | RSS feed + sitemap XML. Uses `page.url` for canonical URLs. |
-| `emoji.odin` | Emoji shortcode expander (`:shrug:` → `¯\_(ツ)_/¯`), post-cmark |
+| `vfs.odin` | Union file system: `VFS`, `build_vfs`, `mount_dir`, `mount_subdir`, `mount_recursive`, `vfs_get`. Layers defaults → modules → site. |
-| `highlight.odin` | Post-cmark Tree-sitter syntax highlighter; statically links HTML/CSS grammars, dlopen for others; caches loaded grammars, reports syntax errors |
+| `assets.odin` | `copy_assets_dir` — iterates VFS entries with `assets/` prefix, minifies CSS, copies verbatim or via `os.copy_file`. |
-| `tree_sitter.odin` | C FFI bindings for Tree-sitter (TSParser, TSQuery, TSQueryCursor, node traversal, dlopen/dlsym). Statically links `tree-sitter-html` and `tree-sitter-css` via Nix. |
+| `opengraph.odin` | `Open_Graph` struct (fields ordered per OGP spec). `og_init(site)` for site defaults, `og_for_page(site, page, base)` for page-specific OG data. |
-| `sectionate.odin` | `wrap_sections` proc — splits HTML at `<h2` into `<section>` wrappers |
+| `frontmatter.odin` | JSON frontmatter parser (`{ }` delimited). Supports `layout` field for template override. |
-| `render.odin` | Template rendering pipeline: pre-parses templates/partials once, struct-based data model (`Base_Data`/`Page_Data`/`Home_Data`/`Posts_Data`), `mustache.render()`, minification gate, RSS, sitemap, robots.txt |
+| `defaults.odin` | `DEFAULTS_PATH` constant, resolved at compile time via `#directory` so bundled templates ship in the binary. |
-| `minify.odin` | Tree-sitter-based HTML and CSS minification (`minify_html`, `minify_css`). Strips comments, collapses whitespace, removes inter-tag spaces. Preserves `<pre>`/`<code>`/`<script>`/`<style>` content. |
+
-| `feed.odin` | RSS feed + sitemap XML generation. Uses `strings.Builder`. `format_rfc822` uses `core:time` for date parsing. |
+### Subpackages
-| `mustache/` | Mustache template engine (spec-compliant, custom implementation) |
+
+| Package | Files | Responsibility |
+|---|---|---|
+| `treesitter/` | `treesitter.odin` | FFI types (`Parser`, `Node`, `Query`, etc.), `@(link_prefix="ts_")` foreign bindings, grammar management (`ensure_parser`, `load_grammar`, `grammar_cache`), statically-linked HTML/CSS grammars |
+| `markdown/` | `markdown.odin` | `Extension` enum, `DEFAULT_EXTENSIONS`, `process(body, ext, file_path)` — full pipeline, `parse_extension_list`, `apply_extension_config` |
+| | `footnotes.odin` | `strip_definitions` (pre-cmark), `inject_notes` (post-cmark) |
+| | `alerts.odin` | `inject_alerts` — GitHub alert blocks (`> [!NOTE]`) → styled blockquotes with semantic class names (`alert-note` etc.) |
+| | `emoji.odin` | `expand_emoji` — `:shortcode:` → unicode emoji |
+| | `sectionate.odin` | `wrap_sections` — splits HTML at `<h2>` into `<section>` wrappers |
+| | `highlight.odin` | Syntax highlighting via tree-sitter. Imports `../treesitter`. |
+| `mustache/` | See [Mustache engine](#mustache-engine) below | Template engine |
 
 Icon SVGs live as HTML partials in `layouts/partials/icons/` (home, github, rss, chevron_up, star).
 
 ### Data flow
 
 ```
-thor.json → find_config → init_site:
+thor.json → find_config → init_site (5-step)
-  1. set defaults (base_url, DEFAULT_MARKDOWN_EXTENSIONS)
+  → build_vfs (defaults/layouts → modules → site/layouts, site/assets)
-  2. parse CLI flags (Flags struct)
+  → site_load_content (scan_content + url computation)
-  3. load config file (Config_File from thor.json)
+  → render_site
-  4. apply_config — non-empty config fields override defaults
+    → load_partials + get_template (VFS + fallback chain)
-  5. apply_cli_flags — flags override config, -ext/-no-ext adjust extensions
+    → render_page_html / render_home_html / render_section
-→ Site (config + Dynamic_Arena + features: bit_set + markdown_extensions: bit_set)
+    → optional minify_html
-                                                                                               ↓
+    → public/
-content/ → walk_content → []Page (with body_html from pipeline)
-                                                                                               ↓
-layouts/*.html → parse() → mustache.Template (parsed once)
-                                   ↓
-render_site → mustache.render(Page_Data, partials) → optional minify_html → public/
 ```
 
-### Config system
+## Page struct
+
+```odin
+Page :: struct {
+    section:     string,      // "" for root, "posts", etc.
+    slug:        string,
+    layout:      string,      // inferred or frontmatter override
+    permalink:   string,      // relative URL path
+    url:         string,      // full canonical URL (base_url + permalink)
+    title:       string,
+    description: string,
+    date:        string,
+    menu:        string,
+    body_html:   string,
+    draft:       bool,
+    is_starred:  bool,
+    _is_index:   bool `private`,
+}
+```
+
+No `Page_Type` enum — page type is inferred from section + `_is_index`. Layout is inferred via `infer_layout(section, is_index)`:
+
+- Home (root index): `"home"`
+- Section index: `"<section>_index"` (e.g. `"posts_index"`)
+- Section page: singularized section (e.g. `"post"`)
+- Root page: `"page"`
+
+**Template fallback chain** (in `get_template`): for content pages, `post → page → base`; for section indexes, `posts_index → section_index → page → base`. Fallbacks logged at debug level. Frontmatter `layout` field overrides the inferred value.
+
+## Config system
 
 Config is split into three structs with a clear 5-step initialization flow:
 
-- **`Flags`** — CLI args only. Parsed by `core:flags`. Includes path overrides, build-mode toggles, and `-ext`/`-no-ext` for markdown extension overrides.
+- **`Flags`** — CLI args only. Parsed by `core:flags`. Includes path overrides (`--content`, `--assets`, `--output`, `--layouts`), build-mode toggles (`-drafts`, `-watch`, `-minify`), and `-ext`/`-no-ext` for markdown extension overrides.
-- **`Config_File`** — parsed from `thor.json` via `json.unmarshal_string`. Holds title, paths, `markdown_extensions` (JSON), `params` (JSON).
+- **`Config_File`** — parsed from `thor.json` via `json.unmarshal_string`. Holds title, paths, `markdown_extensions` (JSON), `params` (JSON), `modules` (JSON array of relative paths).
-- **`Site`** — runtime state: arena, resolved config values, `features: bit_set[Feature]`, `markdown_extensions: bit_set[Markdown_Extension]`.
+- **`Site`** — runtime state: arena, pages, modules, VFS, `features: bit_set[Feature]`, `markdown_extensions: bit_set[md.Extension]`.
 
-**`Feature` enum** — build-mode toggles: `Drafts`, `Minify`, `Watch`. Checked with `.Minify in site.features`.
+**`Feature` enum** — `Drafts`, `Minify`, `Watch`. Checked with `.Minify in site.features`.
 
-**`Markdown_Extension` enum** — content pipeline toggles: `Emoji`, `Sidenotes`, `Alerts`, `Highlight`, `Sections`. Default is `DEFAULT_MARKDOWN_EXTENSIONS` (currently `.Emoji, .Sidenotes, .Alerts`). Configurable via:
+**`markdown.Extension` enum** (in the `markdown` package, not main) — `Emoji`, `Sidenotes`, `Alerts`, `Highlight`, `Sections`. Default is `md.DEFAULT_EXTENSIONS` (currently `.Emoji, .Sidenotes, .Alerts`). Configurable via:
 - `thor.json`: `"markdown_extensions": { "emoji": true, "highlight": false, ... }`
 - CLI: `-ext:highlight,sections` (enable) / `-no-ext:emoji` (disable). Comma-separated, case-insensitive.
 
@@ -74,6 +130,7 @@ Config precedence: `CLI flags > thor.json values > hardcoded defaults`.
   "title": "...",
   "base_url": "...",
   "author": "...",
+  "modules": ["../path/to/module"],
   "markdown_extensions": {
     "emoji": true,
     "sidenotes": true,
@@ -89,7 +146,41 @@ Config precedence: `CLI flags > thor.json values > hardcoded defaults`.
 }
 ```
 
-### Template system
+## VFS (Union File System)
+
+Layered directory resolution for templates and assets: `site layouts/ → module layouts/ → defaults/layouts/`.
+
+```odin
+VFS :: struct { files: map[string]VFS_Entry }
+VFS_Entry :: struct { fs_path: string, data: []byte }
+```
+
+`build_vfs` mounts in reverse precedence (defaults first, site last overwrites). `DEFAULTS_PATH` resolved at compile time via `#directory`, so bundled templates ship inside the binary. Modules configured via `"modules": ["../path"]` in `thor.json` — each module contributes `layouts/` and `assets/` subdirectories. `vfs_get` lazily reads file contents on first access.
+
+Content is **not yet in the VFS** — `scan_content` still uses direct filesystem reads. (See `TODOS.md`.)
+
+## Open Graph
+
+`Open_Graph` struct in `opengraph.odin` with fields ordered per [ogp.me](https://ogp.me/) spec. Site defaults set via `og_init(site)` (site_name, description, default image, locale). Page-specific fields via `og_for_page(site, page, base)` (copies base, overrides url/title/type/is_article/section/published_time). Templates access via `{{og.url}}`, `{{og.title}}`, `{{#og.is_article}}`, etc.
+
+## Markdown pipeline
+
+Lives in the `markdown` package. Entry point: `md.process(body, ext, file_path)`. All `.html` content files skip the pipeline entirely — body is used as-is.
+
+```
+raw markdown
+  → md.strip_definitions     (if .Sidenotes — pre-cmark)
+  → cmark markdown_to_html   (Unsafe mode for HTML passthrough)
+  → md.expand_emoji          (if .Emoji — post-cmark)
+  → md.inject_notes          (if .Sidenotes — post-cmark)
+  → md.inject_alerts         (if .Alerts — post-cmark)
+  → md.highlight_code        (if .Highlight — post-cmark)
+  → md.wrap_sections         (if .Sections — post-cmark)
+```
+
+Each step is gated by `bit_set[md.Extension]`.
+
+## Template system
 
 Templates use Mustache with template inheritance (`{{<base}}` / `{{$block}}`):
 
@@ -97,7 +188,7 @@ Templates use Mustache with template inheritance (`{{<base}}` / `{{$block}}`):
 <!-- base.html -->
 <body>{{> nav}}{{$content}}{{/content}}{{> footer}}</body>
 
-<!-- post.html -->
+<!-- page.html (content layout) -->
 {{<base}}
 {{$content}}
 <main><article><h1>{{page_title}}</h1>{{&body}}</article></main>
@@ -109,50 +200,61 @@ Data is passed as **typed structs** (not `map[string]any`). Mustache resolves st
 
 ```odin
 Base_Data :: struct {
-    now:  datetime.DateTime,
+    now:    datetime.DateTime,
-    body: string,
+    author: string,
-    title: string,
+    params: json.Value,
-    // ...
+    body:   string,
+    title:  string,
+    og:     Open_Graph,
 }
 Page_Data :: struct {
-    using base: Base_Data,  // fields promoted via struct_get fallback
+    using base:   Base_Data,  // fields promoted via reflection fallback
+    page_title:   string,
+    date_iso:     string,
+    date_display: string,
+}
+Home_Data :: struct {
+    using base: Base_Data,
+    pages:      [dynamic]Page_Context,
+}
+Section_Data :: struct {
+    using base: Base_Data,
     page_title: string,
-    // ...
+    posts:      [dynamic]Page_Context,  // flat list; year grouping done in template via pipe
 }
 ```
 
-`render_site` pre-parses all templates and partials once (via `mustache.parse`), then reuses them for every page render.
+`render_site` pre-parses all partials and the base layout once (via `mustache.parse`), then per-layout templates are cached in `get_template`. Year-based grouping on section index pages is done in the template via `{{#posts | group_by year}}` (see Pipes extension below) — there is no `Year_Section` Go-side struct.
 
-**Pipes extension**: section tags may transform the resolved value before iteration via `{{#key | op args…}}`. Pipe filters are parsed into `Node.filters` (allocator-owned by the template) and applied at render time via `apply_pipeline`, with filter results (e.g. `[dynamic]Group` from `group_by`) living in `context.temp_allocator`. Currently only `group_by <field>` is implemented; see `mustache/EXTENSIONS.md`. Used by `posts_index.html` to group posts by year without privileged Go-side data shaping.
+### Pipes extension
 
-### Markdown pipeline (in content.odin `load_page`)
+Section tags may transform the resolved value before iteration:
 
-```
+```handlebars
-raw markdown
+{{#posts | group_by year}}
-  → strip_definitions     (pre-cmark: extract [^id]: definitions — only if .Sidenotes enabled)
+  {{key}}: {{#items}}{{title}}, {{/items}}
-  → cmark markdown_to_html (Unsafe mode for HTML passthrough)
+{{/posts}}
-  → expand_emoji          (post-cmark: :shortcode: → unicode — only if .Emoji enabled)
-  → inject_notes          (post-cmark: [^id] → <label><input><span> markup — only if .Sidenotes enabled)
-  → inject_alerts         (post-cmark: [!TYPE] blockquotes → styled alerts — only if .Alerts enabled)
-  → highlight_code        (post-cmark: tree-sitter per code block — only if .Highlight enabled)
-  → wrap_sections         (post-cmark: wraps content in <section> at <h2> — only if .Sections enabled)
 ```
 
-Each step is gated by `bit_set[Markdown_Extension]`. All `.html` content files skip the pipeline entirely — body is used as-is.
+Currently only `group_by <field>` is implemented. Filter results live in `context.temp_allocator` (render-scoped). See `mustache/EXTENSIONS.md` for syntax details, caps (`MAX_PIPES`, `MAX_PIPE_ARGS`), and the `Group` struct shape.
 
-### Syntax highlighting
+### Comments
+
+`page.html` includes `{{> comments}}`. The `comments.html` partial self-guards with `{{#og.is_article}}` so it only renders on article pages — no separate `is_post` flag.
+
+## Syntax highlighting
 
 Build-time highlighting via Tree-sitter C FFI. No client-side JavaScript.
 
-- **HTML and CSS grammars** statically linked via Nix (`mkGrammarStaticLib` in `thor/flake.nix`). Always available, no dlopen.
+- **HTML and CSS grammars** statically linked via Nix (`mkGrammarStaticLib` in `thor/flake.nix`). Always available, no `dlopen`.
 - **Other grammars** (bash, odin, nu, etc.) loaded via `dlopen` from Helix's compiled `.so` files.
 - Highlight queries (`.scm`) loaded from Helix's runtime directory.
-- Paths hardcoded in `tree_sitter.odin` (Nix store paths, Helix-version-dependent).
+- Paths hardcoded in `treesitter/treesitter.odin` (`GRAPHS_PATH`, `QUERIES_PATH`) — Nix store paths, Helix-version-dependent. (See `TODOS.md`.)
 - Grammar loading split: `ensure_parser` (parser only, used by minify) vs `load_grammar` (parser + query, used by highlight).
 - Capture names mapped to CSS classes: `keyword` → `.hl-keyword`, etc.
 - Atom-one-dark color theme in `main.css`.
 
-### Minification
+## Minification
 
 Optional, enabled with `-minify` flag (`.Minify` in `Feature` bit_set).
 
@@ -160,17 +262,18 @@ Optional, enabled with `-minify` flag (`.Minify` in `Feature` bit_set).
 - **CSS** — tree-sitter parses `.css` files in `assets/`, strips comments, collapses whitespace, trims around `{};:,`. Applied during `copy_assets_dir`.
 - Non-CSS files in `assets/` copied verbatim.
 
-### Memory management
+## Memory management
 
 - `Site` owns a `mem.Dynamic_Arena`
-- `init_site` calls `mem.dynamic_arena_init(&site.arena, alignment = 64)` — the 64-byte alignment is required by Odin's map runtime (`MAP_CACHE_LINE_SIZE`)
+- `init_site` calls `mem.dynamic_arena_init(&site.arena)` (Odin's default alignment suffices)
 - Config loading (flags + JSON) uses the arena allocator explicitly
 - `site_allocator(site)` returns the arena allocator for callers
 - `destroy_site` frees the arena
 - `main.odin` sets `context.logger = log.create_console_logger()` — without this, all `log.*` calls are silently dropped
 - `context.allocator` is set to `site_allocator(&site)` in the main loop
+- `context.temp_allocator` freed per watch-loop iteration via `defer free_all`
 
-### Spall profiling
+## Spall profiling
 
 Optional, compiled out by default. Enabled with `-define:SPALL=true`:
 
@@ -205,23 +308,25 @@ nix build  # runs thor, outputs to ./result/
 
 ```bash
 cd thor
-odin test .              # site tests (config, frontmatter, footnotes)
+odin test .                  # main package tests (site, frontmatter)
-odin test . -all-packages  # includes mustache spec tests
+odin test . -all-packages    # includes mustache specs, lambdas, pipes, markdown tests
 ```
 
 ## Mustache engine
 
-Spec-compliant Mustache implementation at `mustache/`. See `mustache/EXTENSIONS.md` for the non-standard extensions (pipes).
+Spec-compliant implementation at `mustache/`. See `mustache/SPEC.md` for the implementation specification and `mustache/EXTENSIONS.md` for non-standard extensions (pipes).
 
 ### Files
 
 | File | Responsibility |
 |---|---|
-| `mustache.odin` | Public API (`parse`, `render`, `Template`), parser (`parse_section`), renderer (`render_nodes`), template inheritance (`merge_block_overrides`) |
+| `mustache.odin` | Public API (`parse`, `render`, `Template`), parser (`parse_section` with allocator threading), renderer (`render_nodes`), template inheritance (`merge_block_overrides`), `delete_template`/`delete_partials` |
 | `tokenizer.odin` | Tokenizer (template string → `[]Token`), standalone whitespace detection |
-| `data.odin` | Reflection-based data model: `effective` (union/distinct peeling), `lookup_in`, `resolve_name`, `is_truthy`, `any_to_string`, `list_info`, `write_value` |
+| `data.odin` | Reflection-based data model: `base_value` (peels union/any/nested-any layers), `lookup_in` (structs + maps, handles `Type_Info_Any` value kind in maps), `resolve_name`, `is_truthy`, `any_to_string`, `list_info`, `extract_list_element` (unwraps `[dynamic]any` element types so downstream lookups see the real value), `call_interp_lambda`/`call_section_lambda` |
-| `pipes.odin` | Pipes extension: `Pipe_Filter` AST, `parse_pipeline`, `apply_pipeline`, `apply_group_by`. Stored on `Node.filters`; render-scoped results in temp allocator. |
+| `pipes.odin` | Pipes extension: `Pipe_Filter` AST, `parse_pipeline`, `apply_pipeline`, `apply_filter` (switch dispatch), `apply_group_by`. Stored on `Node.filters`; render-scoped results in temp allocator. |
 | `spec_test.odin` | JSON spec test runner — loads `spec/specs/*.json`, runs each test case |
+| `lambda_test.odin` | Spec lambda tests |
+| `pipes_test.odin` | Pipe filter tests |
 
 ### Architecture
 
@@ -233,23 +338,34 @@ render(tmpl, data, partials) → render_nodes (walks flat node array against con
 - **Two-phase API**: `parse()` produces a reusable `Template`, `render()` walks it against data. Templates parsed once, rendered many times.
 - **Flat `[dynamic]Node` array** with `first_child`/`child_count` indices — pre-order layout.
 - **Context stack**: `^[dynamic]any` with `append`/`pop` for section push/pop.
-- **`effective(a)`** peels Named/Distinct/Union layers (including `json.Value`).
+- **`base_value`** peels Named/Distinct/Union layers (including `json.Value`). Also unwraps nested `any`-of-`any` (which occurs when `map[string]any` values are read via runtime map internals).
-- **`lookup_in`** resolves keys on structs (via `reflect.struct_field_value_by_name` with `allow_using = true`) and maps (via runtime map internals).
+- **`lookup_in`** resolves keys on structs (via `reflect.struct_field_value_by_name` with `allow_using = true`) and maps. Detects `Type_Info_Any` value kind in maps and reads the inner any directly to avoid double-wrap.
 - **Template inheritance**: `{{<parent}}` loads parent from partials, `{{$block}}` defines overridable sections. `merge_block_overrides` propagates overrides through multi-level chains.
 - **Dynamic partial names**: `{{>*key}}` resolves partial name from data context at render time.
 
+### Lambdas
+
+Spec-compliant. Stored as `any` values in the data context.
+
+- **Interpolation lambdas**: `proc() -> string`, `proc() -> int`, `proc() -> bool` — called via `call_interp_lambda`, result stringified and escaped.
+- **Section lambdas**: `proc(string) -> string`, `proc(string) -> int`, `proc(string) -> bool` — called via `call_section_lambda` with the raw section text (`node.content`). String result is re-parsed as mustache and rendered against the current context stack.
+
+### Pipes
+
+`{{#key | op args…}}…{{/key}}`. Stored as `[dynamic; MAX_PIPES]Pipe_Filter` on each `Node` (fixed-cap inline storage, no per-tag heap allocation at parse time). Applied in the renderer via `apply_pipeline` before truthiness check. Currently only `group_by <field>` is implemented (returns `[dynamic]Group` where `Group{key, items}`). See `mustache/EXTENSIONS.md`.
+
 ### Not implemented
 
-- Lambdas (`~lambdas.json`)
 - Set delimiters (`{{= =}}`, `delimiters.json`)
 
 ## Known limitations
 
-- cmark allocates via C malloc, not the arena. HTML output leaks until process exit.
+- cmark allocates via C malloc, not the arena. HTML output leaks until process exit (problematic in watch mode — see `TODOS.md`).
 - CSS/JS cache busting uses manual `?v=N` query params instead of content hashing.
-- Tree-sitter grammar/query paths for dynamic grammars hardcoded in `tree_sitter.odin` (Nix store hashes, Helix-version-dependent). HTML/CSS are statically linked.
+- Tree-sitter grammar/query paths for dynamic grammars hardcoded in `treesitter/treesitter.odin` (Nix store hashes, Helix-version-dependent). HTML/CSS are statically linked.
-- `map[string]any` not fully supported by mustache `lookup_in` — thor uses structs instead.
+- `map[string]any` only works through `lookup_in`'s special-case handling; thor otherwise uses structs.
 - `format_f64` in mustache brute-forces shortest float representation.
+- Content directory not mounted in VFS (modules can ship templates/assets but not content packs yet).
 
 ## Design decisions
 
@@ -257,6 +373,7 @@ You may never, *ever* remove `TODO:` or `FIXME:` comments. Those are for humans,
 See `HUGO.md` for analysis of why thor doesn't need Hugo's shortcode context isolation.
 See `mustache/PARTIAL_INDENT.md` for whitespace handling analysis.
 See `mustache/SPEC.md` for the original implementation specification.
+See `mustache/EXTENSIONS.md` for non-standard extensions (pipes).
 
 ## TODO
 

TODOS.md

@@ -6,6 +6,7 @@
 - [ ] Only publish referenced assets.
 - [ ] Split `load_page` into frontmatter-parse + body-process phases so draft pages can skip the markdown pipeline entirely
 - [ ] Use spall to find ways to reduce run time.
+- [ ] Consider using `#soa` for Page lists.
 
 ## Memory Management
 
@@ -28,14 +29,12 @@
 - [ ] Clean up the default layouts
 - [ ] Add `-production` flag
   - sets `-minify`
-- [ ] Open Graph
+- [x] Open Graph
   - [x] mustache data keys for opengraph, etc.
-  - [ ] OpenGraph meta tags — verify all fields match production site
+  - [x] OpenGraph meta tags — verify all fields match production site
-  - [ ] set opengraph tags / description automatically if unset. (Like hugo does)
+  - [x] set opengraph tags / description automatically if unset. (Like hugo does)
-  - [ ] We can't use avatar.jpg as the default site image, that's unique to sbrow.github.io. We need to set that in the frontmatter of content/index.html. or possibly in the config
+  - [x] We can't use avatar.jpg as the default site image.
-  - [ ] Add `og Open_Graph` to `Config_File` and if `Some`, use it as the base
+  - [x] Add `og Open_Graph` to `Config_File`.
-        site og instead of `og_init()`?
-    - If we go this route, `og_init` might not be the best name.
 - [ ] Author should be a struct adhering to https://schema.org/author
 - [ ] Block attributes on code fences (`{ #ex-1 }`) — hello-world.md
 - [ ] include-code shortcode (`{{< include-code ... >}}`) — i-ported-fd-to-odin

content.odin

@@ -17,8 +17,10 @@ Page :: struct {
 	title:       string,
 	description: string,
 	date:        string,
+	lastmod:     string,
 	menu:        string,
 	body_html:   string,
+	og:          Open_Graph,
 	draft:       bool,
 	is_starred:  bool,
 	_is_index:   bool `private`,
@@ -132,10 +134,12 @@ load_page :: proc(
 	page.title = fm.title
 	page.description = fm.description
 	page.date = fm.date
+	page.lastmod = fm.lastmod
 	page.draft = fm.draft
 	page.is_starred = fm.isStarred
 	page.menu = fm.menu
 	page.layout = fm.layout if fm.layout != "" else infer_layout(section, is_index)
+	page.og = fm.og
 
 	if strings.has_suffix(file_path, ".html") {
 		page.body_html = strings.clone(body)

flake.lock

@@ -51,11 +51,11 @@
     },
     "nixpkgs-unstable": {
       "locked": {
-        "lastModified": 1783475452,
+        "lastModified": 1784525419,
-        "narHash": "sha256-3S92fSuv32mjJz2Qb2F4405c21J55F4NIphz5K6hxco=",
+        "narHash": "sha256-yocJ4I4Kd4as0UPMFs9P7laPvvA2x/Bj8EW46iW3VVM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "05988b07fb05cbcb50be6bce197b4b5f75b5e61b",
+        "rev": "a16c3fde2ffeab7f6326f50f460aaffde7ae066d",
         "type": "github"
       },
       "original": {

flake.nix

@@ -62,6 +62,8 @@
             pkgs.tree-sitter-grammars.tree-sitter-html.src;
           css-grammar = mkGrammarStaticLib "tree-sitter-css"
             pkgs.tree-sitter-grammars.tree-sitter-css.src;
+          odin = pkgs.unstable.odin;
+          ols = pkgs.unstable.ols;
         in
         {
           _module.args.pkgs = import nixpkgs {
@@ -108,7 +110,7 @@
             src = ./.;
 
             nativeBuildInputs = [
-              pkgs.odin
+              odin
               pkgs.pkg-config
             ];
 
@@ -143,9 +145,7 @@
           };
 
           devShells.default = pkgs.mkShell {
-            buildInputs = with pkgs; [
+            buildInputs = [odin ols ] ++ (with pkgs; [
-              odin
-              ols
               cmark
               tree-sitter
 
@@ -153,7 +153,7 @@
               unstable.helix
               typescript-language-server
               vscode-langservers-extracted
-            ];
+            ]);
 
             shellHook = ''
               export LIBRARY_PATH="${html-grammar}/lib:${css-grammar}/lib:$LIBRARY_PATH"

frontmatter.odin

@@ -8,11 +8,13 @@ Frontmatter :: struct {
 	title:       string,
 	description: string,
 	date:        string,
+	lastmod:     string,
 	publishDate: string,
-	draft:       bool,
-	isStarred:   bool,
 	menu:        string,
 	layout:      string,
+	og:          Open_Graph,
+	draft:       bool,
+	isStarred:   bool,
 }
 
 // parse_frontmatter splits raw file content into a Frontmatter struct and the
@@ -49,11 +51,13 @@ parse_frontmatter :: proc(content: string) -> (fm: Frontmatter, body: string, ok
 	fm.title       = json_get_string(obj, "title")
 	fm.description = json_get_string(obj, "description")
 	fm.date        = json_get_string(obj, "date")
+	fm.lastmod     = json_get_string(obj, "lastmod")
 	fm.publishDate = json_get_string(obj, "publishDate")
 	fm.draft = json_get_bool(obj, "draft")
 	fm.isStarred = json_get_bool(obj, "isStarred")
 	fm.menu = json_get_string(obj, "menu")
 	fm.layout = json_get_string(obj, "layout")
+	fm.og = json_get_open_graph(obj, "og")
 
 	ok = true
 	return
@@ -77,3 +81,22 @@ json_get_bool :: proc(obj: json.Object, key: string) -> bool {
 	return false
 }
 
+json_get_open_graph :: proc(obj: json.Object, key: string) -> Open_Graph {
+	og: Open_Graph
+	if v, ok := obj[key]; ok {
+		if inner, ok2 := v.(json.Object); ok2 {
+			og.title          = json_get_string(inner, "title")
+			og.type           = json_get_string(inner, "type")
+			og.image          = json_get_string(inner, "image")
+			og.url            = json_get_string(inner, "url")
+			og.description    = json_get_string(inner, "description")
+			og.locale         = json_get_string(inner, "locale")
+			og.site_name      = json_get_string(inner, "site_name")
+			og.published_time = json_get_string(inner, "published_time")
+			og.modified_time  = json_get_string(inner, "modified_time")
+			og.section        = json_get_string(inner, "section")
+		}
+	}
+	return og
+}
+

html.odin

@@ -0,0 +1,137 @@
+package main
+
+import "core:strings"
+
+strip_html_tags :: proc(s: string, allocator := context.allocator) -> string {
+	sb := strings.builder_make(allocator)
+	defer strings.builder_destroy(&sb)
+
+	in_tag := false
+	start := 0
+	for i in 0 ..< len(s) {
+		if s[i] == '<' && !in_tag {
+			if i > start {
+				strings.write_string(&sb, s[start:i])
+			}
+			in_tag = true
+		} else if s[i] == '>' && in_tag {
+			in_tag = false
+			start = i + 1
+		}
+	}
+	if start == 0 {
+		return s
+	}
+	if !in_tag && start < len(s) {
+		strings.write_string(&sb, s[start:])
+	}
+	return strings.to_string(sb)
+}
+
+unescape_html :: proc(s: string) -> string {
+	sb := strings.builder_make()
+	defer strings.builder_destroy(&sb)
+
+	start := 0
+	for i in 0 ..< len(s) {
+		if s[i] != '&' {
+			continue
+		}
+		semi := strings.index(s[i:], ";")
+		if semi < 0 {
+			break
+		}
+		entity := s[i : i + semi + 1]
+		replacement := ""
+		switch entity {
+		case "&amp;":  replacement = "&"
+		case "&lt;":   replacement = "<"
+		case "&gt;":   replacement = ">"
+		case "&quot;": replacement = "\""
+		case "&#39;", "&apos;": replacement = "'"
+		case: continue
+		}
+		if i > start {
+			strings.write_string(&sb, s[start:i])
+		}
+		strings.write_string(&sb, replacement)
+		start = i + semi + 1
+	}
+	if start == 0 {
+		return s
+	}
+	if start < len(s) {
+		strings.write_string(&sb, s[start:])
+	}
+	return strings.to_string(sb)
+}
+
+// generate_summary produces a plain-text summary of an HTML fragment.
+// Blocks (paragraphs, headings, list items) are extracted, their tags
+// stripped, entities decoded, and accumulated word-by-word until the
+// max_words threshold is crossed — at which point the rest of the
+// current block is included before stopping. Mirrors Hugo's default
+// summary behavior.
+generate_summary :: proc(html: string, max_words: int = 70) -> string {
+	separated, _ := strings.replace_all(html, "</p>", "\n\n", context.temp_allocator)
+	separated, _ = strings.replace_all(separated, "</h1>", "\n\n")
+	separated, _ = strings.replace_all(separated, "</h2>", "\n\n")
+	separated, _ = strings.replace_all(separated, "</h3>", "\n\n")
+	separated,_ = strings.replace_all(separated, "</h4>", "\n\n")
+	separated, _ = strings.replace_all(separated, "</h5>", "\n\n")
+	separated, _ = strings.replace_all(separated, "</h6>", "\n\n")
+	separated, _ = strings.replace_all(separated, "</li>", "\n\n")
+	separated, _ = strings.replace_all(separated, "</blockquote>", "\n\n")
+
+	stripped := strip_html_tags(separated, context.temp_allocator)
+	plain := unescape_html(stripped)
+
+	blocks := strings.split(plain, "\n\n", allocator = context.temp_allocator)
+	defer delete(blocks)
+
+	sb := strings.builder_make(context.temp_allocator)
+	defer strings.builder_destroy(&sb)
+
+	word_count := 0
+	first := true
+	for raw_block in blocks {
+		block := strings.trim_space(raw_block)
+		if len(block) == 0 {
+			continue
+		}
+
+		// Collapse internal whitespace to single spaces.
+		block_sb := strings.builder_make(context.temp_allocator)
+		has_content := false
+		in_space := true
+		for c in block {
+			if c == ' ' || c == '\t' || c == '\n' || c == '\r' {
+				in_space = true
+			} else {
+				if in_space && has_content {
+					strings.write_byte(&block_sb, ' ')
+				}
+				strings.write_rune(&block_sb, c)
+				in_space = false
+				has_content = true
+			}
+		}
+		collapsed := strings.to_string(block_sb)
+		words := strings.split(collapsed, " ", allocator = context.temp_allocator)
+
+		if !first && word_count > 0 {
+			strings.write_byte(&sb, ' ')
+		}
+		strings.write_string(&sb, collapsed)
+		word_count += len(words)
+		first = false
+
+		delete(words)
+
+		if word_count >= max_words {
+			break
+		}
+	}
+
+	return strings.to_string(sb)
+}

mustache/EXTENSIONS.md

@@ -58,16 +58,4 @@ Errors (returned as `Data_Error` at render time):
 - **Filter results** (e.g. the `[dynamic]Group` returned by `group_by`) are render-scoped allocations in `context.temp_allocator`. They die with the render call. No caller-side cleanup is needed.
 - The string data inside `Pipe_Filter` (op names, args) is borrowed from the template source — no cloning.
 
-### Future ops (not yet implemented)
 
-The pipe framework is general; additional ops are straightforward to add to `apply_filter` in `pipes.odin`:
-
-- `sort`, `sort_by <field>` — ordering
-- `filter <field> <value>`, `where <field>` — selection
-- `take <n>`, `take_last <n>`, `skip <n>` — slicing
-- `reverse` — order flip
-
-To add a new op:
-1. Implement `apply_<op>(value: any, args: []string) -> (any, Render_Error)` in `pipes.odin`.
-2. Add a `case` to `apply_filter`.
-3. Add tests to `pipes_test.odin`.

opengraph.odin

@@ -1,7 +1,5 @@
 package main
 
-import "core:fmt"
-
 Open_Graph :: struct {
 	title:          string,
 	type:           string,
@@ -10,31 +8,110 @@ Open_Graph :: struct {
 	description:    string,
 	locale:         string,
 	site_name:      string,
-	is_article:     bool,
+	is_article:     Maybe(bool),
 	published_time: string,
 	modified_time:  string,
 	section:        string,
 }
 
-og_init :: proc(site: Site) -> Open_Graph {
+og_for_site :: proc(site: ^Site) -> Open_Graph {
-	return {
+	og := site.og
-		site_name = site.title,
+	if og.site_name == "" {
-		description = site.description,
+		og.site_name = site.title
-		image = fmt.tprintf("%s/avatar.jpg", site.base_url),
+	}
-		locale = "en_US",
+	if og.description == "" {
+		og.description = site.description
+	}
+	if og.locale == "" {
+		og.locale = "en_US"
 	}
-}
-
-og_for_page :: proc(site: Site, page: Page, base: Open_Graph) -> Open_Graph {
-	og := base
-	is_article := page.section != ""
-	og.url = page.url
-	og.title = strip_html_tags(page.title, context.temp_allocator)
-	og.type = "article" if is_article else "website"
-	og.is_article = is_article
-	og.section = page.section
-	og.published_time = page.date
-
 	return og
 }
 
+og_for_page :: proc(site_og: Open_Graph, page: Page) -> Open_Graph {
+	og := site_og
+
+	is_article := !page._is_index
+	if page.url != "" {
+		og.url = page.url
+	}
+	if page.title != "" {
+		og.title = strip_html_tags(page.title, context.temp_allocator)
+	} else {
+		og.title = og.site_name
+	}
+	og.type = "article" if is_article else "website"
+	og.is_article = is_article
+	if page.section != "" {
+		og.section = page.section
+	}
+	if is_article {
+		if page.date != "" {
+			og.published_time = page.date
+		}
+		if page.lastmod != "" {
+			og.modified_time = page.lastmod
+		} else if page.date != "" {
+			og.modified_time = page.date
+		}
+	}
+
+	// Description priority for articles:
+	//   page.og.description > page.description > body summary > inherited
+	// For non-articles (home, section index), inherited site.og.description
+	// is the fallback (matches production behavior — home inherits site
+	// description, section index is empty).
+	description_set := false
+	if page.og.description != "" {
+		og.description = page.og.description
+		description_set = true
+	}
+	if !description_set && page.description != "" {
+		og.description = page.description
+		description_set = true
+	}
+	if !description_set && is_article && page.body_html != "" {
+		og.description = generate_summary(page.body_html)
+		description_set = true
+	}
+	if !description_set {
+		if page._is_index && page.section == "" {
+			// Home: keep inherited site.og.description.
+		} else {
+			og.description = ""
+		}
+	}
+
+	if page.og.title != "" {
+		og.title = page.og.title
+	}
+	if page.og.type != "" {
+		og.type = page.og.type
+	}
+	if page.og.image != "" {
+		og.image = page.og.image
+	}
+	if page.og.url != "" {
+		og.url = page.og.url
+	}
+	if page.og.locale != "" {
+		og.locale = page.og.locale
+	}
+	if page.og.site_name != "" {
+		og.site_name = page.og.site_name
+	}
+	if page.og.published_time != "" {
+		og.published_time = page.og.published_time
+	}
+	if page.og.modified_time != "" {
+		og.modified_time = page.og.modified_time
+	}
+	if page.og.section != "" {
+		og.section = page.og.section
+	}
+	if page.og.is_article != nil {
+		og.is_article = page.og.is_article
+	}
+
+	return og
+}

render.odin

@@ -57,32 +57,6 @@ build_page_context :: proc(page: Page) -> Page_Context {
 	}
 }
 
-strip_html_tags :: proc(s: string, allocator := context.allocator) -> string {
-	sb := strings.builder_make(allocator)
-	defer strings.builder_destroy(&sb)
-
-	in_tag := false
-	start := 0
-	for i in 0 ..< len(s) {
-		if s[i] == '<' && !in_tag {
-			if i > start {
-				strings.write_string(&sb, s[start:i])
-			}
-			in_tag = true
-		} else if s[i] == '>' && in_tag {
-			in_tag = false
-			start = i + 1
-		}
-	}
-	if start == 0 {
-		return s
-	}
-	if !in_tag && start < len(s) {
-		strings.write_string(&sb, s[start:])
-	}
-	return strings.to_string(sb)
-}
-
 load_template :: proc(vfs: ^VFS, virtual_path: string) -> mustache.Template {
 	data, ok := vfs_get(vfs, virtual_path)
 	if !ok {
@@ -176,7 +150,7 @@ render_site :: proc(site: ^Site) {
 		now    = now,
 		author = site.author,
 		params = site.params,
-		og     = og_init(site^),
+		og     = site.og,
 	}
 
 	// Find home page
@@ -289,7 +263,7 @@ render_page_html :: proc(
 	data.body = page.body_html
 	data.date_iso = page.date
 	data.date_display = format_date(page.date)
-	data.og = og_for_page(site^, page, base.og)
+	data.og = og_for_page(site.og, page)
 	return render_template(content_tpl, data, partials)
 }
 
@@ -315,10 +289,7 @@ render_home_html :: proc(
 	data.title = site.title
 	data.body = home.body_html
 	data.pages = list_pages
-	data.og.url = fmt.tprintf("%s/", site.base_url)
+	data.og = og_for_page(site.og, home)
-	data.og.title = site.title
-	data.og.type = "website"
-	data.og.is_article = false
 	return render_template(content_tpl, data, partials)
 }
 
@@ -347,16 +318,17 @@ render_section :: proc(
 		data.body = section_index.body_html
 		data.page_title = section_index.title
 		data.title = fmt.tprintf("%s | %s", section_index.title, site.title)
-		data.og.title = section_index.title
+		data.og = og_for_page(site.og, section_index)
 	} else {
 		data.page_title = capitalize(section)
 		data.title = fmt.tprintf("%s | %s", capitalize(section), site.title)
 		data.og.title = capitalize(section)
+		data.og.description = ""
+		data.og.url = fmt.tprintf("%s/%s/", site.base_url, section)
+		data.og.type = "website"
+		data.og.is_article = false
 	}
 	data.posts = posts
-	data.og.url = fmt.tprintf("%s/%s/", site.base_url, section)
-	data.og.type = "website"
-	data.og.is_article = false
 	return render_template(content_tpl, data, partials)
 }
 

site.odin

@@ -29,6 +29,7 @@ Site :: struct {
 	params:              json.Object,
 	features:            bit_set[Feature],
 	markdown_extensions: bit_set[md.Extension],
+	og:                  Open_Graph,
 }
 
 Feature :: enum {
@@ -51,6 +52,7 @@ Config_File :: struct {
 	markdown_extensions: json.Value,
 	params:              json.Value,
 	modules:             json.Value,
+	og:                  Open_Graph,
 }
 
 // Configuration loaded from command line arguments. Gets folded in to Site
@@ -70,7 +72,7 @@ Flags :: struct {
 }
 
 init_site :: proc(site: ^Site, args: []string) {
-	mem.dynamic_arena_init(&site.arena, alignment = 64)
+	mem.dynamic_arena_init(&site.arena)
 	alloc := site_allocator(site)
 
 	// Set defaults
@@ -107,6 +109,9 @@ init_site :: proc(site: ^Site, args: []string) {
 
 	site_apply_cli_flags(site, _flags)
 	site.config_path = path
+
+	// Build the resolved site-level OG now that every other field is set.
+	site.og = og_for_site(site)
 }
 
 load_config_file :: proc(
@@ -159,6 +164,8 @@ site_apply_config :: proc(site: ^Site, config: Config_File, config_dir: string)
 			}
 		}
 	}
+
+	site.og = config.og
 }
 
 site_apply_path_defaults :: proc(site: ^Site, config_dir: string) {