Risky behavior now covered

Recent desktop fixes (merged in #349) left a few fail-closed branches untested:

• A chat title set by another source during a single in-flight rename is left in place when that rename rejects or succeeds. Draft renames stay local when the server rejects them.
• Leaving the last workspace-watcher subscriber during a restart cancels the restart. A remaining subscriber still gets the replacement watcher.
• POSIX directories are not treated as launchable programs. A missing file still fails closed.
• A throwing workspace-root provider does not drop crash logs. An explicit workspace path overrides the default provider. A sync crash-log write swallows a disk failure.
• Unreadable state.json still resets when the corrupt file cannot be renamed aside.
• The warm-start snapshot cache skips a selected snapshot that exceeds the byte budget, and still keeps a later smaller snapshot after one that does not fit.

Test files updated

• apps/desktop/test/jsonrpc-single-connection.test.ts
• apps/desktop/test/workspace-directory-watcher.test.ts
• apps/desktop/test/launchable-files.test.ts
• apps/desktop/test/local-logs.test.ts
• apps/desktop/test/persistence-state-sanitization.test.ts
• apps/desktop/test/bootstrap-cache.test.ts

Why this reduces regression risk

These paths decide whether a rename clobbers a newer title, a closed workspace keeps a filesystem watcher, a folder open is treated as executing a program, crash logs leak or vanish, corrupt desktop state is discarded, and one large chat blows the warm-start cache. The new tests fail if those guards are removed. No production behavior changed.

Validation

bun run test on the six touched files: 155 pass, 0 fail. Biome check on those files is clean.