Channel Monitor V2 Safe Defaults & Gentle Backfill

Date: 2026-08-08
Status: Approved for implementation
Branch: fix/channel-monitor-v2-ops-ui-blockers (onto channel-monitor-v2)

Problem

H2 — Migration 195 and code defaults set channel_monitor_mode=v2, so every upgrade without an existing key auto-opts into passive V2, stops V1 probes, and may leave users on an empty V2 view.
M1 — First-enable bootstrap forces 5s ticks and ~24h RecomputeRange chunks until now-30d, hammering the primary DB.
Error dedup SQL matches request_id without a created_at bound, scanning ops_error_logs history via candidate_ids.

Topic	Decision
Default mode	v1 (keep active probes). V2 is explicit opt-in.
Existing `channel_monitor_mode=v2` rows	Unchanged (`ON CONFLICT DO NOTHING` / no force rewrite).
Switch to v2	V1 runner `fire()` and `RunCheck` require `ActiveProbesAllowed()` → probes stop.
Backfill	Unified hard gates + adaptive soft gates (same rules, different observed load).
Optional profile knob	Not in this change (YAGNI).

Migration 195_channel_monitor_mode.sql: insert 'v1' when key missing.
If 195 already applied with old checksum, add migration checksum compatibility (do not force rewrite applied DBs to v1).
Code: defaultChannelMonitorMode = v1; empty/invalid normalize → v1.
Frontend Settings form default and public feature flag fallback → v1 when missing/invalid.
Nil settings on V1 RunCheck path remains fail-closed (no probes) for test safety — independent of product default.

Tick interval = refresh_interval (60 or 300s). No 5s bootstrap override.
Each tick: (1) recent overlap (~10m), then (2) at most one historical chunk while product bootstrap incomplete / retention walk ongoing.
Single leader lock; single short transaction budget (~55s).
Chunk ceiling by depth (product phases 90m → 1d → 7d → 30d → silent 90d).

Initial historical chunk: 1h (first seed still 2h for 90m UI).
Min chunk: 15m; max by depth: ≤1d → 2h, ≤7d → 4h, older → 6h.
Success + fast: grow slowly (×1.5) up to depth max.
Failure/timeout: halve chunk; exponential backoff on wait (cap 10m).
Progressive UI: show whatever is covered; bootstrap banner vs 30d product window.

Bound the request_id IN candidate_ids branch with
created_at >= $1 - INTERVAL '90 minutes' AND created_at < $2.