After a mid-turn re-pin, token and content-block traces keep naming the old channel #555

What's wrong (main b82ba630)

• In src/framework.ts, typingChannel is computed once from resolveTurnLocus() when the stream starts (~16289-16295). It is then used as channelId on inference:tokens and inference:content_block traces for the rest of the stream.
• The addressed re-pin at a tool boundary (repinTurnLocus, ~11044-11052) moves the turn's locus mid-stream. After a re-pin, prose goes to the new channel while the traces still name the turn-start one.
• The turn-start comment (~15660-15663) still says the locus is frozen and that mid-turn injections must not redirect prose. That predates the re-pin.

Why it matters

Trace consumers that tag streamed text by channelId attribute the re-pinned round to the wrong conversation. The comment also misleads anyone reasoning about whether injections move routing.

How found

Flagged by the second reviewer in #168's round-4 review. Confirmed by reading; not run.

Possible fix

Derive the trace channelId from the live locus, or update it on repinTurnLocus. Reword the comment.

Found during our review of #168: #168 (review)

_{Posted by the maintainer's desk assistant.}