fix: do not treat unknown presence as machine offline

[slashdevcorpse]

Related issue

Closes #484

Problem / pressure

getOnlineMachineIds() returning null means the presence room did not join. MCP and chat landing treated that as every remote machine offline, including a live PC.

Summary

MCP makeMachineOnlineLookupForMcp and create-options treat null as unknown (usable). Chat landing treats the local probe machine as online, and only claims Offline when presence is synced and there is no heartbeat. Does not sweep other .has() surfaces.

Before / after

Before	After
Presence not joined → MACHINE_OFFLINE and hidden machines.	Unknown is not offline.
Chat landing has() → Offline while syncing.	Offline only when presence is synced and the heartbeat is missing.

Test plan

• corepack pnpm exec vitest run src/mcp/lody-mcp-server.test.ts -t "MACHINE_OFFLINE|shares one remote Machine presence" — 2 passed.
• No chat-landing unit for the callback. No live desktop run.

Context handoff

Instructions for reviewing agents

• Review focus: makeMachineOnlineLookupForMcp in lody-mcp-server.ts and isPresenceMachineOnline in chat-landing.tsx.
• Decisions to challenge: Unknown treated as usable/online rather than a third UI state. Other .has() surfaces (sidebar, settings) are unchanged.
• Plausible failures / evidence gaps: A truly offline remote machine can be listed while presence is joining. Chat landing has no new unit test.

Authoring context

• User goal / directives: Open the remaining false-offline hole as an issue and a small real fix PR.
• Constraints / non-goals: Do not retouch [Bug] Bounded renderer reconnect still paints the PC offline #480/fix(components): keep presence snapshots across bounded reconnect stop #481 snapshot wipe. Do not convert every UI caller to three-state. Do not change Flock sync.
• Risk-bearing decisions: Unknown presence allows create/list of remote machines until RPC fails later.
• Destructive or irreversible behavior: None.
• Deliberately not done or tested: Sidebar/settings/CLI machine list. Live presence-join failure.
• Unknowns / confidence: High on the MCP null path. Medium on chat-landing coverage without a component test.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Include unknown machines in the mobile selector

When presence is not synced on Web/mobile, this callback makes hasNoMachine false and populates selectableMachines from cached machines, but mobileSheetMachineOptions is still sourced from useOnlineMachines() at chat-landing.tsx:3859, which filters strictly to heartbeat IDs in hooks/use-online-machines.ts:23-25. The mobile sheet therefore renders an enabled, non-loading Machine picker with no options, preventing users from choosing or switching to the live remote PC in the exact missing-presence-join scenario this change is intended to support.

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[slashdevcorpse]

Fixed in 498e148. mobileSheetMachineOptions now maps selectableMachines (same source as the desktop picker and hasNoMachine) instead of heartbeat-only useOnlineMachines().