Show terminal-clickable changed files above TUI Current Activity

[roackb2]

Problem

When Heddle edits files in TUI chat, the user currently has to scroll upward through the conversation to find edit previews and understand what changed. The terminal-rendered diff preview is useful for quick confirmation, but it is not ideal for real code review.

Often the user wants to inspect the changed files in a mature IDE/editor. Today that means manually finding the path in the terminal, copying it, and opening it elsewhere.

The screenshot shows an edit preview for:

src/__tests__/integration/tools/tools.test.ts

followed by Recent activity / Current Activity. The changed file path is visible in the older conversation output, but there is no stable, compact changed-files section near the live activity area.

Desired behavior

Add a TUI section above Recent activity / Current Activity that summarizes files changed during the current run/session context.

Example shape:

Changed files
  modified  src/__tests__/integration/tools/tools.test.ts
  modified  src/core/tools/toolkits/coding-files/search-files.ts

The paths should be rendered in a terminal-friendly way so recent terminals can recognize them as clickable file paths. Clicking should open the file in the user's default editor/IDE where supported by the terminal environment.

The goal is likely just to show correct workspace-relative or absolute paths in the right format, not to implement custom click handling.

Placement and UX constraints

• The changed-files section should appear above Recent activity / Current Activity.
• It should be separate from recent activity so large file-change lists do not obscure what Heddle is currently doing.
• It should stay compact by default.
• It should not make live progress harder to see.
• It should handle large edit sessions gracefully, for example by showing the first N files plus a +M more line, grouping by status, or otherwise capping vertical height.
• It should update as Heddle makes changes during a run.

Likely implementation area

Relevant existing pieces:

• TUI panels:
  • src/cli/chat/components/ActivityPanel.tsx
  • src/cli/chat/components/ConversationPanel.tsx
  • src/cli/chat/App.tsx
• Edit preview history formatting:
  • src/cli/chat/utils/format.ts
  • formatEditPreviewHistoryMessage(...)
• Existing workspace diff/review machinery already used by the control plane:
  • src/server/features/control-plane/services/workspace-diff.ts
  • workspaceChanges / workspaceFileDiff routes
  • web review surfaces that show Current workspace changes
• Mutation/diff tracking areas:
  • src/core/agent/mutation-tracking.ts
  • edit-file preview/result metadata from coding file tools

The implementation should prefer reusing existing changed-file detection or diff tracking rather than inventing a second unrelated source of truth.

Acceptance criteria

• While a TUI chat run is editing files, a Changed files section appears above Current Activity.
• The section lists changed file paths with enough status/action context to be useful, such as modified/created/deleted/renamed when available.
• File paths are rendered in a terminal-clickable-friendly format. Prefer workspace-relative paths if those are reliably clickable from the current working directory; use absolute paths if needed for broad terminal/editor support.
• The section updates as additional files are changed during the run.
• Large changed-file lists are capped or summarized so Current Activity remains visible.
• The feature reuses existing diff/change tracking where practical.
• Tests cover changed-file collection/projection and compact rendering behavior.

UX rationale

Heddle already has mechanisms to track diffs and changed files. Surfacing a compact changed-file list in the TUI gives users a quick bridge from agent activity to real code review in their editor, without forcing them to scroll through terminal diff output or copy paths by hand.