Command queue: prioritize user commands over status polls #680

Problem

User commands and status polls share a single FIFO queue (asyncio.Queue in gateway_sessions.py). On busy systems or when the gateway is slow to NACK, a user action (e.g. turning on a light) can be delayed for several seconds while earlier status polls finish.

The is_status_request flag is already present on queued tasks, but it is not used for prioritization.

Current mitigations

Several related issues have already been improved:

• Silent/unresponsive zones are skipped (perf(climate): stop polling heating zones that never answer #555)
• Discovery pacing and poll-on-add suppression (Fresh install without myhome.yaml: lights are never queried, and discovery follow-ups cut status replies short #578)
• Physical gateway climate poll timeouts (fix(climate): eliminate 10s command session timeouts on F455 and add authentic trace fixture (#674) #675)

These reduce how often the queue fills up, but the underlying FIFO behavior remains.

Proposal

Replace the plain FIFO with a priority queue:

• User commands (and any frame with is_status_request=False) are dequeued first
• Status requests are dequeued only when no user commands are waiting
• FIFO ordering is preserved within each class
• The existing “read-back after write” pattern must be preserved: a status request that is queued after a command for the same device must not overtake that command

Acceptance criteria

• A user command queued while status polls are pending is sent before those polls
• A status request queued after a command for the same entity still runs after that command
• Existing tests for queue pacing and silent-zone skipping continue to pass
• No regression on single-session gateways (MH200/MH201)

Related

• Command queue: user commands should go ahead of status polls #553 (original issue, closed after silent-zone mitigation)
• perf(climate): stop polling heating zones that never answer #555, Fresh install without myhome.yaml: lights are never queried, and discovery follow-ups cut status replies short #578, fix(climate): eliminate 10s command session timeouts on F455 and add authentic trace fixture (#674) #675