[teamleaderleo]

W2-15 — fence stale delegated starts on an existing Cloud link

Dependent on backend cmux #30800, which must deploy before this Mac client change lands. Canonical finding: HQ #5353, and W2-15 full result. Draft; no merge/deploy requested.

User failure

Alice grants Bob chat-start permission on a team Cloud VM. Bob attaches: the link stores vmKind: "owner". Alice revokes him. While his original link stays connected, Bob's NEXT app can still initiate a new cmux-managed chat using that stale answer. The existing Rust host gate only sees the answer carried by the old link.

Slice

• Classic CloudAPIClient.chatStartAccess(id) performs read-only GET of the new backend's /api/vm/:id/chat-start-access (returns the caller's owner | granted | none). It does not mint attach tokens or wake the machine.
• For a team Cloud VM whose signed-in user is not the recorded machine creator (or creator is unknown), the Mac refreshes that authorization at the new chat start immediately before the remote start connection. A deleted grant, departed member or account switch refuses before a new agent-session-start; an unavailable permission read fails closed. The original Cloud link's generation/owner check remains in place.
• The creator's own link/start path, SSH hosts, native app-server Cloud links and already-running chats retain their existing behavior. No client-side cached grant is used as authority.
• Regression tests: stale ownerLink + fresh denied grant sends no start, unreadable permission check sends no start, current grant still permits one start, and API client checks GET path / response without an attach.

Limits / required proof

This closes the ordinary NEXT Mac's post-revoke new-start path only. The grant is still separately checked from the daemon's command admission, so revocation can race a just-authorized command, and CLI/other clients using a previously elevated link need a remote-server-validated, revocable action capability for complete fencing. Do not advertise instantaneous all clients revocation based on this slice alone. Team members also retain their separate shared-VM shell access.

Before review/merge: land/deploy #30800; run exact-head Swift tests (AgentTabRemoteStartTests, CloudMachineShareTests) and an Alice/Bob two-identity runtime probe: grant, Bob attach/start A, Alice revoke, Bob start B without reconnect (must refuse), then Bob reconnect (must refuse), with network-read outage and account switch. Local full Mac test environment unavailable here; CI/runtime evidence still pending.

No other owner's branch was overwritten and no production token, permission, spend or VM change was made.

[blacksmith-sh]

Found 9 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmprx54htgr/summary-fail.json (live):/summary-fail.json (live):	View Logs
/tmp/tmpu9kf_96i/summary-missing.json (live):/summary-missing.json (live):	View Logs
[new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows/ [new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows	View Logs
[new_workspaces] the window draws no frames/[new_workspaces] the window draws no frames	View Logs
[tabs] debug.tab_switch timed 0 of 40 switches/ [tabs] debug.tab_switch timed 0 of 40 switches	View Logs
[tabs] the window draws no frames/[tabs] the window draws no frames	View Logs
nightly must build and hand off the macOS 26 helper and Xcode 26.5 app before publishin g/ nightly must build and hand off the macOS 26 helper and Xcode 26.5 app before publishin g	View Logs
test_helper_never_takes_a_hosted_mac_and_skips_compile_on_hit (main.WorkflowTests.t est_helper_never_takes_a_hosted_mac_and_skips_compile_on_hit)/ test_helper_never_takes_a_hosted_mac_and_skips_compile_on_hit (main.WorkflowTests.t est_helper_never_takes_a_hosted_mac_and_skips_compile_on_hit)	View Logs
test_the_repository_highlights_validate (main.DigestTests.test_the_repository_highl ights_validate)/ test_the_repository_highlights_validate (main.DigestTests.test_the_repository_highl ights_validate)	View Logs

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[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

red: cmux-next checks (god files, concurrency, crash safety, l10n); no finished base run on 3154610 to compare; do not merge until green; see lane-rules

[teamleaderleo]

Owned by an agent session · session

[teamleaderleo]

Closing: this classic /api/vm work belongs in cmux-platform, not cmux. Continue it there if still needed.