Client attached to older shared server: -m and /model silently ignored (version mismatch)

v0.52.19-dev client (Eagle) attached via JCODE_SOCKET to a long-running v0.52.0 release server (Brook), same machine.

Symptoms:

• jcode -m claude-sonnet-4-6 launches but session stays on the server's previous model (GPT-5.6 Sol); the -m is silently ignored.
• /model claude-oauth:claude-sonnet-4-6 and the /model picker in the TUI also fail to switch, silently.
• provider-doctor for the same model/route passes all catalog-tier checkpoints including 'Model switch route'.
• Standalone attempt (JCODE_SOCKET= jcode -m ...) printed 'Using model: claude-sonnet-4-6' then died with 'Another jcode server process is already running for runtime dir /run/user/1000'.

Resolution: killing the old 0.52.0 server and letting a fresh server spawn made -m work immediately.

Suggestions: (1) client/server version mismatch should warn loudly or trigger server restart, (2) a failed model switch through the socket should surface an error instead of silently keeping the old model, (3) 'another server running' error could mention which PID/version owns the runtime dir.

Start by reproducing the mismatch with jcode -m, /model, and JCODE_SOCKET using the reported client and server versions. Trace the client/server socket handling and model-switch path, then define done as a visible version or switch error instead of silently retaining the old model; the runtime-owner error may also need PID/version details.