Desktop app: hours-long session transcript permanently lost (not just a display/routing bug)

Follow-up to #93709, which originally reported a project-routing/badge-mismatch bug. During troubleshooting that issue, a separate and more serious problem surfaced: an actual, permanent loss of an hours-long working session, not just a mislabeled or misrouted display.

Environment

• Claude Code desktop app, Code tab
• Platform: WSL2 (Linux) under Windows
• Project involved: a session related to a project directory the account owner calls "prose-voice-editor"

Observed sequence

1. An hours-long session had been in active use in the desktop app, working in a project directory referred to as "prose-voice-editor."
2. While troubleshooting the session-routing bug in #93709, the sidebar began showing inconsistent entries for this project. At one point, an entry in the sidebar rendered with the title "Session disappeared unexpectedly" instead of a normal session title.
3. The sidebar subsequently showed multiple distinct, similarly-named entries under "Ungrouped," including one titled "Prose voice editor -- defunct," separate from an unrelated newer session that also involved the prose-voice-editor project.
4. The account owner located a "Shared session, visible to anyone with the link" URL (https://claude.ai/code/session_01Tpx3ahfRPvc6Z3AoQVUcn2) believed to point to the original session. Opened directly in a logged-in browser, it loaded successfully and showed a real, intact transcript. However, the account owner confirmed this transcript was from a different, newer session created afterward (mid-troubleshooting), not the original lost session. The original session's content could not be located this way.
5. Local, on-machine session storage under ~/.claude/projects/**/*.jsonl was inspected across every project directory present on the machine (via Claude Code itself, run from a terminal) and showed no evidence of missing or truncated files. This only covers local CLI-side storage, though -- the product supports following a session from another device, implying session state may also be server-side/cloud-backed, which could not be inspected this way.
6. The account owner has confirmed that, after all of the above, the original hours-long session is unrecoverable through any means tried so far.

Impact
Permanent loss of substantial, non-reproducible working session content, with no in-app recovery path found (trash/archive, "Open in," and the shared link all failed to surface the original content -- they either don't apply, don't exist for this entry, or resolve to the wrong session).

Relationship to #93709
The session-routing/badge-mismatch bug in #93709 was found first, during the same troubleshooting session, and may or may not share a root cause with this data-loss issue -- that is unconfirmed. Flagging both, and cross-linking, so triage isn't forced to assume they're the same bug.