Rendered Edit Session

Block commits in rendered WYSIWYG mode produce one logical undo step per close/switch/save, not one step per in-session keystroke.

Modules: src/markdown/rendered_commit_undo.rs, src/markdown/editor.rs (commit_session_block), src/state.rs (Tab::apply_rendered_commit_undo_entries)

Problem

central_panel previously called prepare_undo_snapshot_hashed() each frame and record_edit_from_snapshot() when MarkdownEditorOutput.changed. Session buffers keep keystrokes out of tab source until commit, but any path that wrote source mid-frame could still record per-keystroke undo if it ran every frame.

Commit boundary

Undo is recorded when source is mutated at a commit boundary:

Event	Undo step
RenderedEditSession::close_active / switch_to with SaveIfDirty	Yes — via commit_session_block
Enter / lost focus on session TextEdit	Yes — closes active block
Click outside active block (session_dismiss_if_clicked_outside)	Yes
Table cell flush (EditableTable output.changed)	Yes — one step per table write
Keystrokes in active session buffer (on_text_changed)	No
Task checkbox toggle, structural edits	Yes — fallback in central_panel when !undo_recorded

Flow

sequenceDiagram
    participant CP as central_panel
    participant ME as MarkdownEditor
    participant Q as rendered_commit_undo queue
    participant Tab

    CP->>Tab: prepare_undo_snapshot_hashed (non-commit fallback)
    CP->>ME: show()
    ME->>Q: begin_frame (clear queue)
    Note over ME: switch_to_ui → mark_break_before_next_commit
    ME->>Q: record_source_commit (pre-clone → mutate source)
    ME-->>CP: changed, undo_recorded
    CP->>Q: take_pending_commits
    CP->>Tab: apply_rendered_commit_undo_entries
    alt changed && !undo_recorded
        CP->>Tab: record_edit_from_snapshot (structural/checkbox)
    end

1. record_source_commit clones source immediately before mutation and enqueues PendingRenderedCommitUndo.
2. session_switch_to_ui calls mark_break_before_next_commit so the previous block's commit starts a fresh undo group.
3. After show, Tab::apply_rendered_commit_undo_entries sets pending_undo_snapshot from each pre-commit clone and calls record_edit_from_snapshot() (no source_epoch bump — rendered policy).
4. MarkdownEditorOutput.undo_recorded prevents duplicate recording for commits; structural/checkbox paths still use the frame-start snapshot + fallback record_edit_from_snapshot.

Table cells

BlockRef::TableCell commits only signal signal_table_force_commit; the actual source write and undo enqueue happen in render_table when EditableTable sets output.changed.

Undo / redo and epoch

Tab::undo() / redo() bump source_epoch and invalidate session buffers via load_for_epoch. Rendered commits do not bump epoch during normal editing (stable widget ids).

Related

• Core session
• EditHistory
• Undo/redo
• Split view
• Phase 0 epoch policy

Tests

cargo test rendered_commit_undo::
cargo test rendered_session::