feat(tmux): pillbox-styled session chooser with ADR

Add custom formatting to choose-tree (prefix+s) with:
- Catppuccin Mocha colored pills (green=attached, blue=detached)
- Window count with nerd font icon
- Consistent styling with status bar

Document the decision in ADR 0021, including the key constraint
that tmux hardcodes the session name prefix and it cannot be
styled or removed.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: technicalpickles

doc/adr/0021-tmux-pillbox-styled-session-chooser.md

@@ -0,0 +1,86 @@
+# 21. Tmux Pillbox-Styled Session Chooser
+
+Date: 2026-01-28
+
+## Status
+
+Accepted
+
+## Context
+
+The tmux status bar uses a consistent pillbox visual style with Catppuccin Mocha colors—rounded separators, colored backgrounds, and semantic color coding (green for active, blue for info, etc.). The built-in session chooser (`prefix+s`, which invokes `choose-tree -Zs`) uses plain default formatting, creating visual inconsistency.
+
+Goals:
+
+1. Apply pillbox styling to the session chooser for visual consistency
+2. Add semantic color coding (green for attached sessions, blue for others)
+3. Display useful metadata (window count) in a compact format
+
+## Decision
+
+Customize the `choose-tree` format using the `-F` flag with pillbox styling that matches the status bar.
+
+### Implementation
+
+```tmux
+set -g @_icon_windows "󱂬 " # nf-md-dock_window
+set -g @_chooser_format "\
+#{?session_attached,#[fg=#a6e3a1],#[fg=#89b4fa]}\
+#{@_pill_left}\
+#{?session_attached,#[fg=#11111b]#[bg=#a6e3a1],#[fg=#11111b]#[bg=#89b4fa]} \
+#{session_windows} #{@_icon_windows}\
+#{?session_attached,#[fg=#a6e3a1],#[fg=#89b4fa]}#[bg=default]\
+#{@_pill_right}#[default]"
+
+bind-key s choose-tree -Zs -F "#{E:@_chooser_format}"
+```
+
+### Key Constraint Discovered
+
+The `choose-tree` command hardcodes a prefix before the custom format:
+
+```
+(shortcut) indicator session-name: <custom format>
+```
+
+The session name before the colon **cannot be removed, styled, or replaced**. The `-F` format only controls what appears after the colon. This limits alignment possibilities since session names vary in length.
+
+### Alternatives Considered
+
+1. **Include session path in format**
+
+   - Tried: `#{s|$HOME|~|:session_path}` with padding/truncation
+   - Rejected: Path often duplicates session name; varying session name lengths before the colon prevent clean alignment regardless of padding
+
+2. **Pad path to fixed width for alignment**
+
+   - Tried: `#{p-40:#{=/38/...:path}}` (40-char left-aligned field with truncation)
+   - Rejected: Pills align relative to path column, but the column itself shifts based on session name length—the part we can't control
+
+3. **Use fzf-based picker instead**
+
+   - `sesh` already provides this on `prefix+T` with full format control
+   - Rejected for `prefix+s`: Keep the built-in for quick access; fzf picker serves different use case (fuzzy search, zoxide integration)
+
+4. **Include activity/recency timestamp**
+   - Available via `#{t:session_activity}`
+   - Deferred: Adds clutter; may revisit if needed
+
+## Consequences
+
+### Positive
+
+- **Visual consistency**: Session chooser now matches status bar styling
+- **Semantic coloring**: Green pills for attached sessions provide instant visual scanning
+- **Compact metadata**: Window count visible at a glance with icon
+- **Preserves functionality**: Built-in choose-tree behavior unchanged; just styled
+
+### Negative
+
+- **Limited control**: Cannot style or remove the hardcoded session name prefix
+- **Alignment impossible**: Varying session name lengths cause pills to appear at different horizontal positions
+- **Nerd font dependency**: Requires nerd fonts for pill separators and window icon
+
+### Files
+
+- `home/.tmux.conf`: Format definition and keybinding

doc/adr/README.md

@@ -20,3 +20,4 @@
 - [18. switch-to-zoxide](0018-switch-to-zoxide.md)
 - [19. fish-plugin-drift-detection](0019-fish-plugin-drift-detection.md)
 - [20. tmux-prefix-c-space](0020-tmux-prefix-c-space.md)
+- [21. tmux-pillbox-styled-session-chooser](0021-tmux-pillbox-styled-session-chooser.md)

home/.tmux.conf

@@ -184,16 +184,15 @@ set -g status-right-length 100
 # ============================================================================
 # Session Chooser (prefix+s) - Pillbox styled
 # ============================================================================
-# Format: [windows pill] path  (session name already shown by tmux)
-# Colors: green=attached, blue=detached, dim=path
+# Format: [windows pill]  (session name shown by tmux prefix)
+# Colors: green=attached, blue=detached
 set -g @_icon_windows "󱂬 " # nf-md-dock_window
 set -g @_chooser_format "\
 #{?session_attached,#[fg=#a6e3a1],#[fg=#89b4fa]}\
 #{@_pill_left}\
 #{?session_attached,#[fg=#11111b]#[bg=#a6e3a1],#[fg=#11111b]#[bg=#89b4fa]} \
 #{session_windows} #{@_icon_windows}\
 #{?session_attached,#[fg=#a6e3a1],#[fg=#89b4fa]}#[bg=default]\
-#{@_pill_right} \
-#[fg=#6c7086]#{s|$HOME|~|:session_path}"
+#{@_pill_right}#[default]"
 
 bind-key s choose-tree -Zs -F "#{E:@_chooser_format}"