Summary

Add a \ash command that shows a live TUI-style Active Session History view, inspired by Oracle ASH and pg_ash. Works in two modes depending on whether pg_ash is installed.

Motivation

pg_stat_activity polling is already available to any connected user. pg_ash stores historical samples. rpg can surface both in a unified TUI — giving DBAs an ASH-quality view without leaving the terminal.

Design

Command

\\ash

Layer 1 — always available (no extension needed)

• Poll pg_stat_activity every 1s (configurable)
• Live updating stacked bar / sparkline by wait_event_type
• Drill-down hierarchy: wait_event_type → wait_event → query_id → pid

Layer 2 — pg_ash installed

• Detect via SELECT 1 FROM pg_extension WHERE extname = 'pg_ash' or presence of ash.samples
• Time-range slider: zoom in/out on historical data
• Aggregation: 1s buckets recent, 10s/1m/5m for older
• Same drill-down hierarchy works on historical data

Color scheme (matches pg_ash / PostgresAI monitoring — 24-bit RGB)

CPU* = on CPU or uninstrumented wait event (wait_event_type IS NULL in pg_stat_activity).
IdleTx = state = 'idle in transaction'.

Display modes

• Horizontal: time on X axis, AAS on Y, stacked bars by wait_event_type
• Vertical: current snapshot, top N wait events ranked

Key bindings

Drill-down levels

1. wait_event_type (top level — 12 categories)
2. wait_event (within selected type)
3. query_id (top queries within selected wait event)
4. pid (individual session detail)

Acceptance criteria

• \ash launches TUI, exits cleanly on q, Esc, and Ctrl-C
• Live mode works with no pg_ash extension (pg_stat_activity only)
• pg_ash detected automatically; history mode activates when available
• Zoom in/out works in history mode
• Drill-down through all 4 levels works
• Colors match 24-bit RGB scheme above (respects --no-color / NO_COLOR env)
• Works inside alias psql=rpg (is_terminal() guarded)