feat(core): FD-S02, FD-S03 - Add RST and Typst format handlers

SHOULD requirements implemented:
- FD-S02: reStructuredText handler using document_tree crate
  - Parser converts RST elements to unified AST
  - Renderer outputs RST from AST
  - Handles headings, paragraphs, lists, code blocks, emphasis

- FD-S03: Typst handler using typst-syntax crate
  - Parser converts Typst syntax to unified AST
  - Renderer outputs Typst markup from AST
  - Supports math blocks, figures, bibliography features

Both handlers implement Parser, Renderer, and FormatHandler traits.
FFI layer updated for Ada TUI integration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell

crates/formatrix-core/src/ffi.rs

@@ -120,6 +120,22 @@ pub unsafe extern "C" fn formatrix_parse(
                 Err(_) => return FfiResult::ParseError,
             }
         }
+        // FD-S02: RST support
+        SourceFormat::ReStructuredText => {
+            use crate::formats::RstHandler;
+            match RstHandler::new().parse(content_str, &config) {
+                Ok(d) => d,
+                Err(_) => return FfiResult::ParseError,
+            }
+        }
+        // FD-S03: Typst support
+        SourceFormat::Typst => {
+            use crate::formats::TypstHandler;
+            match TypstHandler::new().parse(content_str, &config) {
+                Ok(d) => d,
+                Err(_) => return FfiResult::ParseError,
+            }
+        }
         _ => return FfiResult::UnsupportedFormat,
     };
 
@@ -179,6 +195,22 @@ pub unsafe extern "C" fn formatrix_render(
                 Err(_) => return FfiResult::RenderError,
             }
         }
+        // FD-S02: RST support
+        SourceFormat::ReStructuredText => {
+            use crate::formats::RstHandler;
+            match RstHandler::new().render(doc, &config) {
+                Ok(s) => s,
+                Err(_) => return FfiResult::RenderError,
+            }
+        }
+        // FD-S03: Typst support
+        SourceFormat::Typst => {
+            use crate::formats::TypstHandler;
+            match TypstHandler::new().render(doc, &config) {
+                Ok(s) => s,
+                Err(_) => return FfiResult::RenderError,
+            }
+        }
         _ => return FfiResult::UnsupportedFormat,
     };
 

crates/formatrix-core/src/formats/mod.rs

@@ -6,12 +6,18 @@ pub mod markdown;
 pub mod djot;
 pub mod orgmode;
 
-// These will be implemented incrementally
+// FD-S02, FD-S03: SHOULD requirement implementations
+pub mod rst;
+pub mod typst;
+
+// FD-S01: AsciiDoc - to be implemented
 // pub mod asciidoc;
-// pub mod rst;
-// pub mod typst;
 
 pub use plaintext::PlainTextHandler;
 pub use markdown::MarkdownHandler;
 pub use djot::DjotHandler;
 pub use orgmode::OrgModeHandler;
+
+// SHOULD handlers
+pub use rst::RstHandler;
+pub use typst::TypstHandler;