[santoshkumarradha]

Summary

A launch after the dev channel replaced the binary took about 15 s. The old host had retired itself, but it held the workspace lock while it saved its conversations, and it had already closed its socket. The new launch saw the lock held and assumed a host was starting. It waited the full 10 s birth wait, then opened the conversation in its own process.

 Host.shutdown
+  close listener, remove socket, release workspace lock
   for each conversation: Close   # waits for its last save, up to 30 s
-  close listener, remove socket, release workspace lock

 Attach
   lock free  -> spawn, wait for socket
-  lock busy  -> wait 10 s for a socket
+  lock busy  -> wait for a socket, and ask for the lock again on each turn;
+                when the holder lets go, spawn once

Each conversation still holds its own journal lock until its save finishes, so a new host cannot open a conversation that is still being written. The second change covers hosts from older builds, which still save while holding the lock.

A retiring host also holds a new host.saving lock from before it gives the slot up until its last conversation is closed. Retire and Stop (waitForGone) wait up to 1 s more on that lock once the slot is free, so an ordinary save finishes before the new host reopens those journals. The launch path never waits on it. The full suite caught this need: TestDifferentEnvironmentRestartsIdleRealHostAndReopensJournals failed without it.

Evidence

Tests count states and order, not time (internal/enginehost/handover_test.go):

• TestARetiringHostLetsGoOfTheWorkspaceBeforeItsSaveFinishes: the host retires while a conversation's Close is blocked. The test checks that the lock is free, that a second host can start, and that the first host's late exit leaves the new socket in place.
  Before: the host kept the workspace lock while its conversation was still saving. After: pass.
• TestRetireWaitsForTheSaveOfTheHostItAskedToGo: while the save is still running, the slot is free and Retire has not returned. Retire returns after the save.
• TestALaunchStartsTheHostOnceAHolderOnItsWayOutLetsGo: the lock is held with no socket, Attach starts waiting, then the lock is released. The test checks that exactly one host is spawned and Attach connects to it.
  Before: engine host: no host answered (after 10 s). After: pass.

Rig on Spark (copied codeaf home, fresh 240k-file folder so the first save is slow): open the folder, quit, engine --stop, then launch again 1 s later.

	first frame	engine --stop	client engine
dev 334cab9	11.03 s	gave up after 10 s: "the host is still holding this workspace"	in-process (vision line in the client's own stderr at +10 s)
this branch (d4db04e)	0.51 s	1.04 s (1 s save grace, then returns)	new host; the old host keeps saving alongside it and exits on its own

In the dev run, the client's goroutine dumps show enginehost.waitForHost < Attach < localLink.dial < remote.Roam from 0.2 s to 10 s. The old host logged the same line as the laptop did: could not finish saving this chat: still saving this chat on this computer: context deadline exceeded.

Full suite: make check (LC_ALL=C) on Spark, fleet job 20261026-192124-002488, commit d4db04e. Every enginehost test passes, plus -race -count=20 on the new tests and the environment-restart test. Failures:

• Already failing on dev: internal/release (2), internal/seniordev/util TestFindUpRootFirst.
• Flaky under suite load, both pass alone (10/10 and 5/5): cmd/codeaf TestRunInCellSealsItsCallsAndContinuesFromThem (TempDir cleanup) and internal/syncsetup TestR7PersonalLeaderFallbackAndNoAutomaticRegain.

Merge Danger

Door: two-way

Blast Radius: host handover

Retire and Stop now return when the workspace is free and its saves are done, or 1 s after the slot frees, whichever comes first. Before, they waited up to 10 s and then failed. A launch that comes during a slow save and asks for the conversation still being written gets the existing "open in another window" landing: a new conversation with the held row armed. Before, it waited up to 10 s and then opened the conversation in its own process.

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