riabuild 2026.09.23

What's Changed

• docs(agents): describe the UI and UX of riabuild agents in DESIGN.md by @lowerkinded in #171
• fix(agents): leave the shell prompt at the top after exiting, not the bottom by @lowerkinded in #174
• fix: agents UI — no extra space from the caret, out-of-usage warnings for every provider, and Esc interrupts a running turn by @lowerkinded in #170
• fix(agents): a draft per row, start-up failures in the pane, token totals, a stable rail by @lowerkinded in #175
• feat(agents): NEW SESSION offers exactly the signed-in sign-ins; remove the chooser by @lowerkinded in #176
• feat(agents): show a turn as launching, thinking or running a tool by @lowerkinded in #177
• feat(agents): quitting takes a second q or Ctrl-C within five seconds by @lowerkinded in #173
• docs(agents): copying out of riabuild agents is the terminal's own selection by @lowerkinded in #172
• fix(harness): read Grok's streaming-json as it is documented, not as ACP by @lowerkinded in #178

Full Changelog: v2026.09.21...v2026.09.23