feat(chat): keep the execution machine visible in the main chat

[coygeek]

Summary

Show the selected thread's execution machine in the main chat, including after the thread has started. The machine name is available in the new-thread composer, but the reported ongoing projectless thread relies on a small sidebar icon for machine context.

Problem to solve

When the same thread is viewed from two computers, the main chat can look the same on both. Users need to know which machine owns the execution environment and will run commands or access files. A small sidebar icon is easy to overlook and requires attention away from the conversation.

On T3 Code Nightly 0.0.46-nightly.20261004.2657, the investigator observed a new-thread composer with a named "Run on" control. Opening an existing running projectless thread removed that named control from the main chat. The user supplied screenshots of the ongoing thread on both computers and then recognized the machine indicator in the left sidebar. The concern is discoverability, rather than an established routing failure.

Proposed behavior

Keep a readable execution-machine name visible within the main chat for the selected existing thread, near the composer or in another persistent chat location. Apply this to projectless threads as well as threads associated with a project.

Identify the machine that owns the thread's execution environment. Viewing a thread from a different computer must not change the indicated execution machine. A readable name should provide the context without requiring a hover, opening another panel, or consulting the sidebar.

Preserve the existing new-thread machine selection behavior. For an existing thread, the indicator can be informational and need not allow changing where the thread runs. If the execution environment cannot be identified, show that uncertainty instead of claiming that execution is on the viewing computer.

Acceptance criteria

• Open an existing projectless thread owned by Machine B from a T3 Code client on Machine A. The main chat visibly names Machine B without hovering or opening another panel.
• Open that same thread from a client on Machine B. The main chat still identifies Machine B as the execution machine.
• Switch to a thread owned by Machine A. The chat indicator updates to Machine A and does not retain the previous thread's machine name.
• Collapse the left sidebar. The selected thread's execution machine remains readable in the main chat.
• Verify the indicator for running and completed threads, with and without an associated project.
• Confirm that the existing new-thread "Run on" selection remains usable and that the displayed machine for an existing thread agrees with its actual execution environment.

Affected area

The main chat's persistent execution-environment context, including the existing-thread composer and projectless threads.

Non-goals

Changing command routing, migrating a running thread to another machine, or replacing the existing sidebar indicators. No incorrect routing or simultaneous execution on two computers was established by this investigation.

Alternatives considered

• Keep the sidebar icon as the only persistent cue. This preserves the current layout but leaves the reported discoverability problem in the main chat.
• Show the name only on hover or in a details panel. This provides more information on demand but requires an extra action before the user can identify where commands will run.
• Keep a readable machine name in the main chat. This is the preferred option because it supplies the needed context while the user reads and sends messages.

Supporting context

Both computers were directly checked and had the same exact Nightly version, 0.0.46-nightly.20261004.2657. The investigator directly inspected the client on Machine A and observed the named new-thread "Run on" control followed by its absence from the existing running thread's chat composer. The screenshots from both computers were supplied by the user. The supplied comparison screenshot also shows the named control below the new-thread composer.

Read-only database inspection found the selected thread in Machine B's current store and did not find it in Machine A's inspected stores. Machine B also had a running T3 server with a child Codex app-server process, and the selected thread's latest persisted run was marked running. This supports the execution-environment association without establishing that any individual command was executed during the investigation.

The user corrected the initial bug interpretation after noticing the sidebar machine indicator. This request is therefore a usability feature, with one outcome: readable execution-machine context in the main chat. The original screenshots are omitted because they contain unrelated conversation content and identifying details; the relevant observations are recorded above.

Related reports cover adjacent behavior: #4124 was addressed by #4217 for remote project toolbars; #8218 proposes sidebar colors; #14711 concerns choosing the machine for a new projectless draft. This proposal focuses on a readable machine name in an existing chat after it starts, including local and projectless threads and when the sidebar is collapsed.