chore: add changesets for the snapshot stall and recovery fixes

Author: elkaix

.changeset/snapshot-stall.md

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+---
+'@pymodel/pythinker-code': patch
+---
+
+Stop the session snapshot request from timing out on busy sessions. Each recorded event no longer pays a fresh file open and close, the watermark is read without waiting for pending writes, and the session list is scanned in parallel, so opening or refreshing a session stays fast even with a long history. This was most visible on Windows, where the per-event file cost is highest.

.changeset/web-snapshot-recovery.md

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+---
+'@pymodel/pythinker-code': patch
+---
+
+Recover the web and desktop app when a session snapshot request fails. It is now retried with a growing delay instead of leaving the todo list and the sub-agent list frozen until a reload, and a failed task refresh reports itself rather than failing in silence.