galaxy/specs/APP-3904/TECH.md

TECH.md — APP-3904: Don't override pane/tab representation for expanded edit tool call

Problem

When an agent edit tool call is expanded into a pane (via ExpandEditToPane), the vertical tabs sidebar changes its representation for that tab from the original pane (e.g. "Create Korean Poem File" with agent icon and metadata) to a generic "Requested Edit" code-diff pane. The entire sidebar row — title, icon, subtitle, badge — changes to reflect the replacement CodeDiffPane instead of the original agent conversation pane.

The sidebar should continue showing the original pane's full representation while a temporary replacement is active.

Relevant code

• app/src/pane_group/pane/code_diff_pane.rs:22-45 — CodeDiffPane::from_view hardcodes PaneConfiguration title to "Requested Edit"
• app/src/workspace/view.rs:6428-6460 — open_code_diff creates the CodeDiffPane and calls replace_pane with is_temporary: true
• app/src/pane_group/tree.rs:55-112 — HiddenPane / HiddenPaneReason::TemporaryReplacement tracks the original→replacement mapping
• app/src/pane_group/tree.rs:368-372 — PaneData::is_temporary_replacement checks if a pane is a replacement
• app/src/pane_group/mod.rs:4456-4502 — PaneGroup::replace_pane orchestrates temporary replacement; original stays in pane_contents
• app/src/workspace/view/vertical_tabs.rs:2065-2136 — PaneProps::new resolves display properties (typed, title, subtitle, icon, badge) from the pane's configuration and type
• app/src/workspace/view/vertical_tabs.rs:2348-2391 — PaneGroup::resolve_pane_type maps PaneId → TypedPane which drives icon/badge/kind

Current state

The ExpandEditToPane feature flag controls how code diff views are opened:

• Enabled: The focused pane is temporarily replaced with a CodeDiffPane. The original pane is hidden via HiddenPaneReason::TemporaryReplacement(replacement_id) and kept in pane_contents for later restoration.
• Disabled: The diff opens in a new tab.

When the sidebar renders tab rows, PaneProps::new resolves all display properties from the visible pane. For a temporary replacement, the visible pane is the CodeDiffPane, so the sidebar shows:

• Icon: WarpIcon::Diff (instead of the original terminal/agent icon)
• Title: "Requested Edit" (hardcoded in CodeDiffPane::from_view)
• Type: TypedPane::CodeDiff (loses all terminal-specific metadata like conversation title, working directory, git branch)
• Badge/subtitle: empty

The pane header ("Requested Edit" with Refine/Done/Accept buttons) shown inside the pane content area is correct and is rendered by CodeDiffView::render_header_content — that is not affected by this change.

Proposed changes

1. Add original_pane_for_replacement lookup to PaneData

In app/src/pane_group/tree.rs, add a method that returns the original hidden pane's ID given a replacement pane ID:

pub fn original_pane_for_replacement(&self, replacement_pane_id: PaneId) -> Option<PaneId>

This scans hidden_panes for a TemporaryReplacement entry whose associated replacement ID matches. It follows the same pattern as the existing is_temporary_replacement method.

2. Expose through PaneGroup

In app/src/pane_group/mod.rs, add a thin delegation method:

pub fn original_pane_for_replacement(&self, replacement_pane_id: PaneId) -> Option<PaneId>

3. Update PaneProps::new to use original pane for display

In app/src/workspace/view/vertical_tabs.rs, modify PaneProps::new so that when the requested pane_id is a temporary replacement, it resolves the PaneConfiguration and TypedPane from the original hidden pane:

let display_pane_id = pane_group
    .original_pane_for_replacement(pane_id)
    .unwrap_or(pane_id);
let display_pane = pane_group.pane_by_id(display_pane_id)?;
let pane_configuration = display_pane.pane_configuration();
let typed = pane_group.resolve_pane_type(display_pane_id, app);

This makes the sidebar row render the original pane's icon, title, subtitle, badge, and all terminal-specific metadata (conversation title, working directory, git branch, status indicators).

Fields that should still use the replacement pane_id:

• pane_id — click/focus targets the visible replacement pane
• is_focused — the replacement pane is what actually holds focus
• is_being_dragged — drag state belongs to the visible pane

End-to-end flow

1. User is in an agent conversation (terminal pane, sidebar shows "Create Korean Poem File" with agent icon)
2. Agent produces an edit tool call; user expands it
3. open_code_diff creates a CodeDiffPane and calls replace_pane(focused_pane_id, new_pane, true), which:
   • Adds the original terminal pane to hidden_panes as TemporaryReplacement(replacement_id)
   • Swaps the tree node to the CodeDiffPane
4. Sidebar re-renders. PaneProps::new receives the replacement pane_id:
   • Looks up original_pane_for_replacement(pane_id) → finds the hidden terminal pane
   • Resolves typed, pane_configuration, title, icon, etc. from the original terminal pane
   • Sidebar row shows "Create Korean Poem File" with agent icon and metadata (unchanged)
5. User accepts/rejects the edit → close_temporary_replacement_pane reverts to the original pane
6. Sidebar naturally shows the original pane again (no special handling needed)

Risks and mitigations

• Original pane removed prematurely: For temporary replacements, replace_pane explicitly skips removing the original from pane_contents. The original pane is guaranteed to exist for lookup. No new risk.
• Multiple temporary replacements: If multiple diffs are expanded in sequence on the same pane, the previous replacement is reverted first (via close_temporary_replacement_pane) before a new one is created. The lookup remains 1:1.
• Non-ExpandEditToPane path: When the flag is disabled, diffs open in a new tab (not a replacement). original_pane_for_replacement returns None, and PaneProps::new falls through to the existing behavior. No regression.
• Detail sidecar: The detail sidecar (hover popup) also resolves from PaneProps. Using the original pane's type means the sidecar will show terminal-specific detail (working directory, git branch, etc.) instead of code-diff detail. This is the correct behavior since the tab still conceptually represents the agent conversation.

Testing and validation

• Manual: expand an agent edit tool call with ExpandEditToPane enabled. Verify the sidebar row keeps the original pane's icon, title, subtitle, and any badges. Verify clicking the sidebar row still focuses the diff pane. Verify accept/reject restores the original pane normally.
• Manual: repeat with ExpandEditToPane disabled. Verify no regression — diff opens in a new tab with "Requested Edit" title as before.
• Unit test: Add a test in tree_tests.rs for original_pane_for_replacement — verify it returns Some(original_id) after a temporary replacement and None otherwise.

Follow-ups

• Consider whether CodeDiffPane still needs a hardcoded "Requested Edit" title at all, since the pane header text comes from CodeDiffView::render_header_content independently. The PaneConfiguration title is only relevant when the pane is shown in a new tab (non-replacement path). Leaving it as-is is safe.