shellState stays .unknown — dedup records state before panel exists, suppressing all subsequent reports

[arzafran]

Tracking upstream cmux manaflow-ai#6618 — verified FIX_NOW (exists in our fork, ship-ready).

Complexity: small

Evidence (our code): Sources/TerminalController.swift:15368-15380 — shouldPublishShellActivity is called and state recorded off-main before main.async; Sources/Workspace.swift:7648 — guard panels[panelId] != nil else { return } silently drops the update if panel not yet registered; Sources/Workspace.swift:6730-6741 — resolveCloseConfirmation returns fallbackNeedsConfirmClose (Ghostty confirm-close) when state is .unknown, producing spurious close-confirmation dialogs.

Proposed fix: In Sources/TerminalController.swift:15368-15380, move the socketFastPathState.shouldPublishShellActivity(...) call and dict update inside the DispatchQueue.main.async block, after confirming the panel is registered. Only record the state in the dedup dict when updateSurfaceShellActivity actually applies the update (panel found). If the panel is absent the first time, the next identical report must not be suppressed. Alternative: make updateSurfaceShellActivity/updatePanelShellActivityState return Bool and call shouldPublishShellActivity only on true.

Upstream: manaflow-ai#6618