[idea] Dynamic tab labels via template support ({cwd_basename}, {terminal_title}) while preserving manual names

[carlosmoradev]

Summary

Add support for template variables (such as {cwd_basename} or {terminal_title_stripped}) in tab labels under [ui], applying only to auto-named tabs and respecting user-assigned manual names.

[ui]
# Dynamic label for tabs that have not been manually renamed.
# Falls back to positional number when empty or unset.
tab_label = "{cwd_basename}"

The Problem

In multi-repo or agentic setups, users frequently navigate between repositories or run agents in distinct project directories. Static numbering (1, 2, 3) forces the user to remember which tab hosts which project, leading to disorientation.

Attempting to solve this externally with shell hooks (precmd, chpwd) or agent wrappers calling herdr tab rename hits major architectural walls:

1. Permanent custom-name freeze: Per No way to clear a tab's custom name: tab.rename permanently freezes auto-numbering and the dim tab-bar style #3470 and Custom tab and workspace names can't be removed: no "Clear name" action, and saving an empty rename is a no-op #3252, calling tab.rename sets custom_name = Some(...) irrevocably, freezing auto-numbering, breaking the DIM tab-bar styling, and making transient decorations permanent.
2. Subprocess & agent spawning: Background tools, subagents, and long-running multiplexer panes bypass shell interactive alias/hook layers.
3. Loss of user intent: Blindly renaming tabs clobbers strategic labels manually set by the user (e.g., naming a tab "Argos" or "Hotfix-Prod").

Because Herdr already tracks pane state live (CWD via OSC 7 / procfs, and terminal_title for window_title and the sidebar), resolving this inside the multiplexer is the cleanest path.

Proposed Design

1. Template-driven tab_label in configuration

Introduce a tab_label setting under [ui] in config.toml that accepts template variables already familiar from window_title:

• {cwd_basename} — e.g. gentle-shell, backend, frontend
• {cwd} — full working directory path
• {terminal_title} / {terminal_title_stripped} — dynamic title reported by shell / agent
• {index} / {number} — tab position index (current default behavior)

2. Strict respect for custom_name

• Auto-named tabs (custom_name.is_none()): Dynamically evaluate tab_label based on the focused pane's state. If the template is unset or resolves empty, retain the current position number.
• Manually named tabs (custom_name.is_some()): The user's explicit name takes precedence. The template is ignored.

3. Clear/Reset path for custom names (#3470)

Allow resetting a custom name back to auto-naming:

• CLI: herdr tab rename <tab_id> --reset
• Socket RPC: accepting label: null (or an explicit tab.reset_name method) to set custom_name = None.
  This allows users (or transient scripts) to hand the tab back to the dynamic template without restarting the session.

Edge Cases & Decisions

• Multi-pane tabs: Follow the active/focused pane's CWD/title (consistent with the rule window_title already uses).
• Tab label width cap: An optional tab_max_width = 24 (or truncation with ellipsis) would prevent long directory names from overflowing the tab bar.
• Performance: CWD / title changes only trigger a tab re-render for the active tab or on focus change, avoiding overhead during high-output commands.

[dariocurr-lexroom]

I'd like this too: I use Herdr desktop 0.1.13 on macOS with several Claude Code and Codex sessions, and numeric tab labels make it hard to tell the sessions apart. I'd like unnamed tabs to follow the AI session name, including later renames or a new session in the same tab, while keeping manually assigned tab names.

The related tab-title request was redirected to Ideas; I realize this discussion concerns the terminal version, but the same need exists in the desktop app. Given the desktop contribution policy, should desktop users handle this entirely through a personal tab-bar mod, or would you consider it for the shipped tab bar?

I would be happy to work on this if it is a change you would consider accepting; please let me know the preferred scope and contribution path before I start.