#36044 cmux-tui: the owner's Native dial carries a Cloud chat's folder copy; outdated only when older

Leo's first Cloud chat on NIGHTLY 036f8aa5 failed at "Clone repository" with "cloud-chats-3 runs an older cmux that can't take this chat yet. Update the machine to move it." (Leo: "4+ situations end to end", "where's all our ergo").

Cause (read on the machine): cloud-chats-3 runs b24aac2c, the app's own bundled cmux-tui. Since cmux-platform#824 the app's Cloud link is a signed Native owner dial, and identify on that carrier lists only the agent carrier's 36 capabilities (native_owner.rs CAPABILITIES), so cmux link start-chat copy read fs-v1 as missing and answered machine_outdated. The app's automatic update then found nothing older (not_older) and the copy failed again. The entry also refused the fs.* frames themselves on that dial.

Fix:

• native_owner: identify on the owner's carrier also lists fs-v1 (symlink, deflate, no-follow), git-seed-v1, git-seed-export-v1 and blob-fetch-v2, while the host serves them (the carrier filters identify's own advertised set).
• fs_wire / remote_entry: on a Native dial only the owner's (vm_kind owner) may send a file, seed, blob or cloud.repo.* frame, as a line and as a byte-stream dial (native_dial_admits). A team or unverified Native dial is refused them (remote_denied). Classic dials keep the entry gate's answer as before.
• link/machine_gate: machine_outdated ("update the machine") only when the machine's build_time is older than this client's, as machine update --if-older orders them. Otherwise machine_capability_missing, whose message names the capability. Used by sync, seed push/pull, access and agent move.

Tests: native_data_frames_reach_only_the_owner (owner admitted; team and unverified Native dials refused every data frame; classic dials unchanged; the carrier lists the capabilities), only_an_older_machine_is_outdated.

Scope decision (coordinator, for Leo's ask): the owner principal only, never shared or team guests.

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Fixes Cloud chat folder copies failing on the app's own build, and makes "update the machine" errors only apply to actually older machines.

Previously, cmux link start-chat copy on a Native owner dial read fs-v1 as missing because the owner's carrier identify didn't list file capabilities, so it answered machine_outdated even when the machine was current. Now the owner's carrier lists file, seed, and blob capabilities, and only the owner's Native dial may send those frames. Separately, machine_outdated is now only reported when the machine's build is older than the client's; otherwise the error is machine_capability_missing and names the capability.

• Adds an older flag to the outdated check, comparing build_time against this client's like machine update --if-older does.
• Adds machine_capability_missing for current machines that still lack a capability.
• Updates sync, seed push/pull, access, and agent move paths to use the new distinction.
• Adds tests for owner-only native data frames and the older-machine rule.