feat: follow Markdown file links and heading fragments

docs/architecture.md

@@ -12,6 +12,7 @@ One crate; no workspace or terminal-coordinate types in the editing backend:
 - `files`: owns the gitignore-aware directory/file catalog, authoritative OS paths, compact tree projection, query filtering, browse/search focus, expansion/selection restoration, navigation, and scan/error state shared by floating and docked presentations.
 - `clipboard`: owns native plain-text provider selection and bounded subprocess I/O; it never computes selections or editing offsets.
 - `syntax`: owns Tree-sitter grammar detection, per-buffer incremental trees, bundled highlight/local/injection queries, and syntax byte spans; it has no terminal color/geometry or editing dependency.
+- `markdown`: owns native Markdown link/reference resolution, local destination decoding, and heading fragment lookup through the installed block/inline grammars. It has no editor lifecycle, terminal, LSP, or external-process dependency.
 - `plugin`: owns generic document snapshots/events, zero-based grapheme positions, diagnostics, frontend-independent semantic token kinds/modifiers, and versioned asynchronous update contracts. Semantic token updates are native-only, not part of the Ruby wire protocol; it has no LSP protocol types.
 - `lsp`: owns opt-in native server workers, bounded framed JSON-RPC, synchronization/capability negotiation, settings, UTF-16/file-URI conversion, definition/hover results, and semantic token requests/legend decoding. Its private configuration resolver supplies presets without restricting language IDs.
 - `session`: `EditorSession` owns the editor, native LSP, and Ruby hosts together. It loads configuration once, registers eligible plugins before installing shared bindings, tracks document open/change/save/close events, polls native and plugin results, validates versioned diagnostics/navigation, and retires failed plugin ownership.
@@ -27,6 +28,7 @@ Frontends inspect `palette()` for the optional read-only query, filtered command
 Frontends use cached `selection_navigation_hint()` for command lists and `file_navigation_hint()` for the active file view/context, without reconstructing input policy.
 Frontends inspect `count()` for the optional pending motion prefix; parsing and counted motion dispatch remain editor-owned.
 Frontends inspect `leader_pending()` for the cached display of a pending leader sequence; prefix recognition, cancellation, and dispatch remain editor-owned.
+Frontends inspect `g_pending()` for the built-in Normal `gf` prefix. Markdown following preflights links and headings before buffer/caret mutation; an unloaded target is validated/prepared once, while loaded targets use their current unsaved text. File identity and activation stay editor-owned.
 Frontends inspect `buffer_id()`, `buffer_count()`, `has_buffer(id)`, and the ascending-ID `buffers()` iterator of borrowed path/dirty/active metadata. Existing text, cursor, selection, search, and mode methods describe only the active buffer.
 Frontends inspect `file_picker()` for query, presentation, view, explorer-local INSERT/filter subfocus, selection, and errors, and iterate borrowed `FileRow` metadata (actual path, display label, directory flag, visible depth, expansion). Dock side is a logical preference. They allocate rectangles, add folder suffixes/colors, and render; hierarchy, filtering, parent/child navigation, focus transitions, and selected-file opening remain backend-owned.
 Frontends inspect `diagnostics()` and `diagnostic_at_cursor()` for validated active-buffer annotations. Diagnostics are owned by core LSP or a plugin and buffer revision; text changes clear them. Native server retirement removes only that server's contribution, preserving sibling diagnostics. The TUI underlines annotated text, colors affected gutter numbers by severity, and displays the primary caret's diagnostic message without replacing search/selection backgrounds.

docs/configuration.md

@@ -55,6 +55,8 @@ Key notation follows [Herdr's readable style](https://herdr.dev/docs/configurati
 
 `ctrl+i` aliases `tab`, and `ctrl+m` aliases `enter`, including inside leader sequences. Ctrl+h and Ctrl+j are distinct control keys, not Backspace/Enter aliases. Only a single modifier on an ASCII letter is supported. Arbitrary non-leader key sequences, Alt/Cmd/Super, combined modifiers, modified special keys, and Vim-style angle-bracket notation are rejected rather than silently treated as another key.
 
+The built-in Normal `gf` sequence follows Markdown file links. It is not a configurable general sequence prefix: bind `config.core.follow_link` to a single key or leader sequence to add another route. A configured or disabled Normal `g`, or choosing `g` as the leader, overrides the built-in prefix.
+
 ## Action reference
 
 | Available modes | Methods on `config.core` |
@@ -62,6 +64,7 @@ Key notation follows [Herdr's readable style](https://herdr.dev/docs/configurati
 | Normal | `insert`, `append`, `open_below`, `open_above` |
 | Normal, Visual | `insert_first_nonblank`, `append_line_end`, `clone_above`, `clone_below` |
 | Normal | `join_lines`, `undo`, `redo`, `command` |
+| Normal | `follow_link` |
 | Normal | `lsp.definition`, `lsp.diagnostics`, `lsp.hover` |
 | Normal | `search`, `paste_before`, `paste_after` |
 | Normal | `paste_system_before`, `paste_system_after` |

docs/development.md

@@ -33,6 +33,7 @@ Rust embeds the Ruby implementation at compile time: [`ruby_values.rb`](../src/r
 Rust tests live alongside their modules; native LSP integration checks are in [`tests/lsp.rs`](../tests/lsp.rs).
 
 - Editor checks cover Unicode editing, multi-target state, undo/redo, saving failures, and modal paste acceptance and rejection atomicity.
+- Markdown navigation checks cover inline/reference destinations, escaped/percent-encoded paths, heading markup and duplicates, same-document fragments, dirty target reuse, failed navigation atomicity, primary-only following, and `gf` prefix cancellation/configuration overrides.
 - Session and Ruby checks exercise real Ruby execution, command/capability ownership, effect validation, configuration fallback, plugin retirement, crash/timeout recovery, and inherited-pipe cleanup.
 - Unix terminal-hook checks use isolated child processes and real PTYs to keep process-global hooks out of the parallel runner. They cover cleanup on entry failure, normal return, I/O errors, and panics, including original panic-payload propagation.
 - Native LSP integration checks launch framed-protocol fixture subprocesses, covering initialization/settings, opt-in startup, synchronization, UTF-16/file-URI conversion, dirty targets, stale requests/diagnostics, and transport failures. Stack checks cover independent initialization, diagnostic merging/clearing, sibling failure isolation in active/parked buffers, same-revision rename/close identity, aggregate limits, first-server position routing, and both shutdowns. Semantic ordering uses protocol/file gates; elapsed deadlines only bound stuck subprocesses.

docs/editing.md

@@ -16,6 +16,7 @@ Default controls and editing behavior. For custom bindings, see [configuration](
 | Normal, Visual | `I` (Shift+i) / `A` (Shift+a) insert at first nonblank / line end; Visual splits each touched row into a caret first |
 | Normal | `h`/`j`/`k`/`l` or arrows move every caret; `0`/`$` or Home/End |
 | Normal | `w`/`b`/`e` move every caret to next word start, previous/current word start, word end; `W`/`B`/`E` for whitespace-delimited WORDs |
+| Normal | `gf` follows a Markdown file link or heading fragment at the primary caret |
 | Normal, Visual | Decimal prefixes repeat cursor/word/search motions: `5j`, `3k`, `2w`, `4e`, `2n`; Esc cancels a pending count |
 | Normal | `J` (Shift+j) joins each targeted line with the next line |
 | Normal | `x`/Delete delete; `u` undo; `U` (Shift+u) redo; `:` enter command mode |
@@ -170,6 +171,22 @@ Esc or Ctrl+p cancels without changing text, selections, the previous command/se
 
 Space begins a leader sequence in Normal/Visual by default. Press the suffix keys in order; nested prefixes wait without a timeout. The status bar shows the pending sequence. Esc cancels the sequence and pending count without leaving Visual or collapsing carets. See [leader configuration](configuration.md#leader-key) for remapping and declaration rules.
 
+## Markdown links
+
+Normal `gf` or `:follow_link` follows the link under the primary caret, without an LSP. Inline links and full/collapsed/shortcut reference links are supported; reference definitions can appear elsewhere in the document. The label or destination can be under the caret. Images, code blocks, and ordinary text are not file links.
+
+Local paths resolve relative to the source file, not the working directory; percent-encoded UTF-8 paths and Markdown-escaped punctuation are decoded. Targets can be any supported text file. Existing buffers are reused, including unsaved text and files removed from disk. Missing files, undefined references, invalid destinations, or missing headings report an error without switching buffers or moving carets.
+
+`[Section](#section)` stays in the current document; `[Section](other.md#section)` opens the target and moves to its heading. ATX and Setext headings use GitHub-style slugs derived from visible inline text: lowercase, punctuation removed, whitespace replaced by hyphens, and duplicate suffixes `-1`, `-2`, etc. Heading lookup uses unsaved target text. Relative file links require a named source; same-document fragments also work in unnamed buffers.
+
+External URL schemes/network paths are rejected; this action never launches a browser or shell. Numeric HTML entities and common named entities (`amp`, `lt`, `gt`, `quot`, `apos`, `nbsp` and their supported aliases) are decoded; other recognized named entities report an unsupported-entity error rather than guessing. Unicode slugs/reference matching use standard-library case conversion, not a complete Unicode case-fold/category table.
+
+`g` waits for `f`, shows in status, and Escape cancels. Other input cancels the prefix and follows ordinary input handling. A configured Normal `g` binding overrides this built-in prefix. Custom bindings use the generated action:
+
+```ruby
+config.bind "leader f", config.core.follow_link
+```
+
 ## Syntax highlighting
 
 Buffers highlight automatically using [Tree-sitter](https://tree-sitter.github.io/tree-sitter/) and compiled-in grammar/query packages. The selected language set is Rust, Ruby, Python, JSON, Bash, Makefile, Markdown, JavaScript/JSX, TypeScript/TSX, HTML, CSS, YAML, TOML, C, C++, and Go. Detection uses filename/extension or the in-memory first-line shebang, including common special filenames such as Makefile, Gemfile, and Cargo.lock; no file reread occurs. Unsupported formats use the normal foreground. The detected language appears in status, and save-as redetects it.