[Bug]: Composer shows Markdown markers on styled text but they can't be edited #29561

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web (mobile not checked)

Root cause

The ** shown beside styled text in the rich text composer looks like editable text, but it isn't in the document.

The editor stores styled text as a ProseMirror mark. decorationsForSelection in apps/web/src/components/ComposerPromptEditorTiptap.tsx draws each marker as a widget decoration while the caret is in that range. .composer-rich-marker sets user-select: none and pointer-events: none, so the marker cannot be clicked, selected, or changed.

docs/user/composer.md adds to the confusion by saying markers "stay in the text". That is true of what the agent receives, but not of what can be edited in the composer.

Steps to reproduce

1. Leave Settings → Chat → Rich text composer on.
2. Type **bold** in the composer.
3. Click the word bold. The ** markers appear beside it.
4. Try to click, select, or change one of the markers.

Expected behavior

Markers revealed by the caret behave like the text they appear to be. As in the MarkText desktop editor, clicking into formatted text exposes its Markdown so it can be edited in place. For example, changing ** to * makes the text italic, and deleting the markers removes the formatting.

Actual behavior

The markers can't be selected or edited. The only way to edit them directly is to turn off Settings → Chat → Rich text composer, which removes styling from the whole composer. The source toggle that addressed this was added in #26777 and reverted in #27390.

Impact

Minor bug or occasional failure

Version or commit

T3 Code v0.1.6 (desktop). Code inspected at main @ 8657eec.

Environment

Windows 11

Suggested approach

While the caret or selection is inside a styled range, show that range as real Markdown text, and parse it back into marks when the caret leaves. serializeEditorDoc and parseInlineMarkdown already convert in both directions.

This changes editor behavior as well as fixing a mismatch, so caret stops, input rules, and undo history would all need checking. This has not been prototyped.

Workaround

Turn off Settings → Chat → Rich text composer while editing formatting.