feat: add --tabname flag for per-tab isolation within a single daemon

[halmisen]

Summary

• Adds a --tabname <name> global flag that routes any command to a named, persistent browser tab within the same daemon instance
• Each named tab maintains its own isolated element ref map, active frame context, and cross-origin iframe sessions — no state bleeding between tabs
• A new tab_name_list action returns all registered named tabs with URL, title, and liveness

Motivation

The current --session/--session-name mechanism provides isolation at the daemon/process level (separate Chrome instances). --tabname provides tab-level isolation within a single browser instance, which is useful when:

• An AI agent drives multiple sites simultaneously (e.g. cross-referencing two pages)
• A workflow needs several persistent, named browser contexts without the overhead of launching multiple Chrome processes
• Tests need to interleave commands across tabs in a predictable, named fashion

How it works

agent-browser --tabname reddit open reddit.com
agent-browser --tabname hn    open news.ycombinator.com
agent-browser --tabname reddit snapshot   # isolated ref map, not polluted by hn
agent-browser tab_name_list               # list all named tabs

• First use of a name creates a new browser tab; subsequent commands reuse it
• If the backing page was closed externally the slot is re-created transparently
• The daemon's shared ref_map / active_frame_id / iframe_sessions are swapped in/out around every command — all existing action handlers work unchanged (zero risk of regression for non-tabname usage)
• AGENT_BROWSER_TAB_NAME env var is an alternative to the CLI flag

Changes

File	Change
cli/src/flags.rs	Add tab_name: Option<String> field + --tabname parsing + env var
cli/src/commands.rs	Inject tab_name into command JSON when flag is set
cli/src/native/element.rs	Add #[derive(Clone)] to RefMap (required for per-tab state save/restore)
cli/src/native/browser.rs	Add find_page_index_by_target_id, switch_to_target, active_target_id helpers
cli/src/native/actions.rs	Add NamedTabState, named_tabs field in DaemonState, setup/save helpers, tab_name_list action

Test plan

• --tabname foo navigate <url> creates a new named tab and navigates it
• Second call with same --tabname foo reuses the existing tab
• --tabname a snapshot and --tabname b snapshot return independent ref maps
• tab_name_list returns both tabs with correct URLs
• Commands without --tabname continue to work exactly as before
• Named tab with a closed backing page is re-created transparently

Background

This feature was originally built as a TypeScript implementation in the BUNotesAI/agent-browser-session fork and is re-implemented here natively for the Rust daemon.

[vercel]

Someone is attempting to deploy a commit to the Vercel Labs Team on Vercel.

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[vercel]

The --tabname CLI flag violates the project's mandatory kebab-case convention for multi-word CLI flags, making it inconsistent with all other flags.

[vercel]

When a named tab's backing browser page dies and is recreated, stale element references, frame IDs, and iframe sessions from the dead page are restored to the new page, causing invalid state.