ProjectRegistry.removeConnection is reentrant, and the connection registry is keyed by descriptor #292

Found during the independent review of #291. Pre-existing — not introduced by that PR — but worth fixing on its own, because the daemon's outbound channels are now keyed by descriptor too, which makes a wrong-descriptor write more consequential than it was.

The interleaving

ProjectRegistry.removeConnection iterates a copy of connectionProjectPaths[id] with an await per store. While it is suspended:

1. Another connection's .openProject of a new path runs joinSidebars.
2. That inserts the departing sidebar into the new store — connectionProjectPaths[X].insert(B) plus storeB.addConnection(X, fdX).
3. The removal loop never sees B, because it is walking a snapshot taken before.
4. close(fdX) runs anyway.

storeB is then left holding X → fdX indefinitely. Every later broadcast for project B goes to whichever connection has since been handed that descriptor number — including a one-shot CLI, which would print the first graphChanged it sees as though it were its own project's.

It needs the app disconnecting at the same instant another client opens a new folder, so it is rare. No deterministic failing test yet — this is reasoning from ProjectRegistry.swift:128-137 and :390-397.

Suggested fix

Two parts, from the review:

• Key the connection registry by connection UUID rather than by file descriptor. Every caller already has the UUID, and it is the identity that is actually stable — a descriptor number is reused the moment it closes. This applies to OutboundChannels as well, whose global map is descriptor-keyed today.
• Re-read the path set after each await in removeConnection, rather than iterating a snapshot taken before suspending.

Why not in #291

#291 is already large and touches the same files; folding a registry-wide re-keying into it would make it unreviewable. Its own descriptor-recycling hazards are closed (open refuses to inherit a dead channel, send refuses an unregistered descriptor, close refuses a descriptor it has no channel for), so this is the remaining structural half rather than an open hole.

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https://claude.ai/code/session_01BP43ags4cn8fq2ZZdv85J9