[BUG] Tab autocompletes folder and closes picker; can't drill into folders

[hannesrudolph]

Type

Bug

Problem / Value

When adding context, pressing Tab or Enter on a folder autocompletes the folder name and immediately closes the picker. This prevents users from drilling into a folder to select deeper files via keyboard, adding friction to building precise paths.

Context

Affects users selecting files/folders via "@" in a new task. Users trying to navigate into nested folders by keyboard can't expand a folder without the picker closing. Reported behavior includes that using backslashes shows a subset of items, while forward slashes don't consistently list contents; overall, users end up typing full paths which is slower and error-prone.

Reproduction

1. Start a new task
2. Type "@" to add file/folder
3. Begin typing a path and select a folder from suggestions
4. Press Tab
   Expected: Stay in the picker, autocomplete the folder segment, and show the folder's contents to continue narrowing.
   Actual: The picker closes and the selection ends, forcing full path typing to go deeper.

[hannesrudolph]

Closed #4058 as duplicate. Tracking here.

[hannesrudolph]

Hey @roomote-agent,

Summary of cause:

• Enter/Tab in the picker routes through handleKeyDown() which calls handleMentionSelect(). For concrete items (including folders), the menu is explicitly closed via setShowContextMenu(false) at [webview-ui/src/components/chat/ChatTextArea.tsx:345].
• The insertion uses insertMention(), which always appends a trailing space after the mention (see [webview-ui/src/utils/context-mentions.ts:68-73]). That trailing space immediately causes shouldShowContextMenu() to return false due to the unescaped whitespace check at [webview-ui/src/utils/context-mentions.ts:388-389]. Net result: the picker closes and will not stay open to drill into the selected folder.
• The only place that keeps the menu open is the category branch (File/Folder/Git) when there is no value yet (drill-in prompt), see [webview-ui/src/components/chat/ChatTextArea.tsx:332-343]. There is no special-case for a concrete folder value.

Proposed approach:

1. In handleMentionSelect(), when selecting a Folder with a concrete value:
   • Ensure the inserted path ends with "/".
   • Insert the folder mention without a trailing space (either trim the one added by insertMention() or construct the mention manually for this case).
   • Do not call setShowContextMenu(false); keep it open.
   • Place the caret after the trailing slash and immediately issue a search for the updated query, mirroring the existing flow at [webview-ui/src/components/chat/ChatTextArea.tsx:601-606], so the folder’s children repopulate under the same picker.
   • Optionally setSelectedMenuIndex(0) and keep selectedType null; getContextMenuOptions() will blend fuzzy matches with dynamic results.

Why this works:

• No trailing space keeps shouldShowContextMenu() true.
• Not closing the menu preserves the picker for continued keyboard navigation.
• The immediate search repopulates entries with the folder’s contents so users can drill down.

Edge cases:

• Paths with spaces are already handled by escaping in insertMention().
• Keep leading "/" normalization and enforce a trailing slash for folders for consistent matching.

If helpful, I can sketch the exact conditional in handleMentionSelect() and a test that simulates selecting a folder via Enter and asserts the picker remains open and input ends with "@/path/to/folder/" (no space).