fix: mount-list dedup (BA-650 / #3593) regressed in SessionSpec refactor — KernelRow.mounts no longer deduped at enqueue

Read src/ai/backend/manager/repositories/scheduler/creators.py at SessionRowCreator.build_row, especially the resolved_mounts assignment and KernelRow.mounts construction. Compare it with the original deduplication in #3593, then check the legacy registry.py:1075 enqueue path for the same gap. Done means persisted mounts are deduplicated in both write paths; user-facing GraphQL behavior is already described as unaffected.

Summary

The mount-list deduplication added in #3593 (BA-650) was partially lost during the sokovan session-lifecycle / SessionSpec refactor (#11250). The write/enqueue path no longer deduplicates mounts before persisting it to KernelRow.

Background

#3593 deduped the compute-session mount list in two places, both via a set-comprehension [*{mount.name for mount in ...}]:

1. Read path — models/session.py :: parse_row (GraphQL session resolver)
2. Write path — registry.py :: enqueue_session (persisted KernelRow.mounts)

Current state (main, after #11250)

Read path — still correct, even strengthened. Now at src/ai/backend/manager/api/gql_legacy/session.py:1103:

"mounts": [*{mount.name for mount in vfolder_mounts}],
"vfolder_mounts": [*{vf.vfid.folder_id for vf in vfolder_mounts}],  # newly deduped too

Write path — regressed. The enqueue_session payload was refactored into SessionRowCreator.build_row, and the set-dedup was dropped. src/ai/backend/manager/repositories/scheduler/creators.py:110:

resolved_mounts = list(self.kernel_spec.vfolder_mounts)
...
mounts=[mount.name for mount in resolved_mounts],   # ← no dedup (was [*{...}])

Impact

• The persisted KernelRow.mounts column can again contain duplicate folder names — the exact condition #3593 fixed.
• User-facing GraphQL responses are NOT affected: parse_row re-derives mounts from vfolder_mounts with dedup at read time, so compute_session / compute_session_list still return unique values.
• Any consumer that reads the stored mounts column without going through parse_row would observe the duplicates.

Suggested fix

Restore the set-comprehension at the write site to match #3593:

mounts=[*{mount.name for mount in resolved_mounts}],

The legacy registry.py enqueue path (registry.py:1075, mounts=mount_entries built by _mount_entries_from_creation_config) should be checked for the same gap while at it.

References

• Original fix: #3593 (BA-650)
• Regressing refactor: #11250 (8321c79aa, creators.py:110)