feat(tui): show tokens per second in assistant message footer

[thdxr]

This PR adds tokens per second (tok/s) display to the TUI assistant message footer.

Changes

• Added index prop to AssistantMessage component to enable efficient backwards iteration through message list
• Modified duration memo to stats memo that returns both duration and total output tokens
• Tokens are accumulated from all assistant messages since the parent user message
• Display format: {duration} · {tps} tok/s

Implementation

• Single backward loop starting from current message index
• Accumulates tokens from assistant messages between user message and current message
• Exits immediately when parent user message is found
• Only shows tok/s when output tokens > 0

[bxb1337]

this will be great. why its not merged yet?

[andrewdunndev]

Clean implementation. The backward loop from the current message index is efficient.

One edge case I hit when building something similar: the first few tokens of a response produce unstable tok/s values (small elapsed time, large variance). A minimum output token threshold before displaying (e.g., skip if output < 10 tokens) avoids showing misleading rates like "2,000 tok/s" from a single token arriving quickly.

Also, for cumulative session-level token visibility (total in/out across all turns), would that fit as a separate footer element or is per-message the intended scope?

[0serna]

This would be great. are there any plans to merge these changes?

[rekram1-node]

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