🪲 BUG-#28: Last assistant message missing after a tool call

[FernandoCelmer]

Description

• media/dom.js — Adds renderedAssistantText, tracking cumulative text actually rendered in the panel across the turn (alongside the existing turnEndSeen).
• media/chat-turns.js — finishAssistantTurn() appends the closed bubble's rawText into renderedAssistantText.
• media/app.js / media/composer.js — done no longer discards its fallback outright when turnEndSeen is true. It diffs message.text (the full cumulative answer from the RPC response) against renderedAssistantText and flushes only the un-rendered remainder, resetting both trackers per turn.

Motivation and Context

turnEndSeen was a plain boolean, set once on the chat/turnEnd notification fired before a tool call and never reset until the turn's done event. When the trailing segment after a tool call never streamed via chat/textDelta — only arriving in the final RPC response text — done's fallback was forced to undefined, silently dropping the last assistant message with no bubble ever created for it.

Closes #28.

Types of changes

• Bug fix (change that fixes an issue)
• New feature
• Documentation

Checklist

• I have performed a self-review of my own code
• I have added tests that prove my fix is effective
• I have updated the CHANGELOG
• I have updated the documentation accordingly

[FernandoCelmer]

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