TUI side pane: list of connected clients with per-connection metrics

[sunng87]

Goal

Add a toggleable side pane to the --tui view that lists every tracked connection (the connected PostgreSQL clients) with per-connection state and traffic counters, so you can see who is connected at a glance and act on a specific client.

Today the TUI shows only aggregate metrics in the header (conns_live, totals, rate sparkline via metrics.summary() in src/state.rs:303). The per-connection data already exists — MetricsSnapshot::connections: Vec<ConnSnapshot> (src/state.rs:53) — but it is never rendered. This issue surfaces it.

Data source (already available)

The registry already retains everything the pane needs:

• ConnSnapshot { id, client: SocketAddr, server: SocketAddr, lifecycle, encrypted, msgs_in, msgs_out, bytes_in, bytes_out } (src/state.rs:45)
• ConnectionLifecycle::{ Open { since }, Closed { since, ended } } (src/state.rs:27)

The pane should read metrics.snapshot() (src/state.rs:317) rather than summary(). Performance note / design point: unlike summary() (which deliberately avoids touching connection records), snapshot() walks the registry under its lock and allocates a Vec every frame. Decide how to keep this cheap:

• Only call snapshot() while the pane is open (preferred — closed pane pays nothing), and/or
• Throttle to a few times per second rather than every frame.

The default connection cap is large (DEFAULT_CONNECTION_CAP = 10_000, src/state.rs:15), so the pane must virtualise/scroll rather than render thousands of rows.

Layout

The current layout is purely vertical: title(5) / log(Fill) / footer(3) (src/tui.rs:486). The pane splits the middle row horizontally, keeping the title and footer full-width:

• Position — left vs right. Right keeps the existing left-aligned message flow anchored and matches the "detail rail" convention. Left surfaces clients first. Slight preference for right.
• Width — a bounded Constraint, e.g. Min(24)..Max(40) or a percentage with sensible small-terminal fallback (collapse/hide below a threshold width).
• Resize — optional, follow-up; a fixed sensible default is fine for v1.

Per-client row content

For each connection, show:

• Client endpoint — client.ip and client.port (the primary identity; the display filter keys off these, src/filter.rs:74).
• Lifecycle — Open/Closed with colour (e.g. green live, dim/grey closed) and age from since. Decide whether closed connections appear at all; if so, how they are sorted/dimmed relative to live ones.
• Encryption — a marker for encrypted (relevant in mitm mode; distinguishes the decrypted sessions from cleartext pcap ones).
• Traffic — compact per-connection bytes_in/bytes_out (reuse the human() formatter, src/tui.rs:711) and/or message counts.

server addr and per-connection message counts are secondary; show server addr only when width allows or when it differs from the default upstream.

Interaction / scoping the log

The display-filter subsystem (#13) already parses client.ip == ... and client.port == ... (src/filter.rs:8). Make the pane the ergonomic entry point for that:

• j/k (or arrows) to move the selection within the pane.
• Enter on a client applies a client.ip == <ip> and client.port == <port> display filter, scoping the message log to that one connection. Esc/clear returns to the unfiltered view.
• Optionally, the header's existing conns_live counter links to the pane (e.g. it becomes the pane's title/cap summary).

Decide whether selecting a client filters immediately on Enter (explicit) or on navigation (live preview). Preference: explicit Enter, consistent with the existing filter UX.

Keybinding

The pane needs a toggle. The keyspace is getting crowded — relevant existing bindings in normal mode: c clears events, f follow, r rich, w wrap, y filter-edit (src/tui.rs:418). Candidates:

• Tab / Shift-Tab to focus-cycle into the pane (clean, no letter conflict, scales if more panes are added later), or
• C (capital) / s for clients/side.

Preference: Tab to toggle, with the pane collapsing to a thin status column when unfocused (so a key like j/k always maps to log scroll unless the pane is focused). No startup flag needed for v1; default off to preserve current behaviour.

Scope

TUI only. The line-oriented stdout output (pcap/mitm without --tui) is unaffected. No change to the metrics/state layer's public API beyond (optionally) reading snapshot() from the TUI.