Live factory start should always run startup backfill after subscribing

[miyaontherelay]

Problem

factory start --mode live subscribes from now, but currently only runs the startup runOnce() full pull when the event high-watermark route is unavailable.

When the high-watermark route works, pre-existing Ready issues or pre-existing GitHub mirror Linear issues can be missed until a new event fires.

Observed with AgentWorkforce/relayfile-adapters#224 mirrored as Linear AR-311: the live daemon was healthy and subscribed, but the already-existing issue was not dispatched.

Expected

Live startup should register subscriptions first, then always run a startup backfill/full pull, buffering events while the backfill runs. The existing high-watermark fallback logic already has most of this shape, but it should not be gated only on route unavailability.

Acceptance criteria

• factory start / factory start --mode live subscribes before backfill.
• Startup backfill runs even when event high-watermark is available.
• Buffered live events drain after the backfill.
• Tests cover an issue that exists before live start and does not emit a new event.

Related

• Source GitHub issue used in repro: GitHub: export shared mount-path parser for issues and PRs relayfile-adapters#224
• Linear mirror observed in repro: AR-311

[miyaontherelay]

Related routing fallback issue: #31. Related Linear label preservation issue: AgentWorkforce/relayfile-adapters#226.