[Bug] FileStore tag manager ignores the table branch, so branch tags are not protected from snapshot expiration

[thswlsqls]

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Paimon version
master @ bbae07d / 2.2-SNAPSHOT

Compute Engine
Engine-agnostic (core); surfaces via Flink/Spark rollback procedures

Minimal reproduce step

1. Create a primary-key table, commit once on main.
2. table.createBranch("branch1"), branchTable = table.switchToBranch("branch1"), commit once.
3. branchTable.createTag("branch_tag", 1), then commit twice more.
4. Expire with snapshot.num-retained.min/max = 1 via branchTable.newCommit("").expireSnapshots().
5. Read branchTable.copy(scan.tag-name = branch_tag): fails with FileNotFoundException: manifest-list-....

Cause: AbstractFileStore.newTagManager() (line 369) passes DEFAULT_MAIN_BRANCH to TagManager, while snapshotManager() (line 190) and AbstractFileStoreTable.tagManager() (line 817) use the table branch. newExpireSnapshots() (line 485) hands that main-branch manager to ExpireSnapshotsImpl.collectTaggedSnapshots() (line 454), which never sees branch tags.

What doesn't meet your expectations?
Branch tags should protect their snapshots, as on main. Instead the tagged snapshot's manifest list and data files are deleted.

Anything else?
Same root cause: automatic tags and _SUCCESS files of branch tables land in the main tag/ directory, and Flink RollbackToProcedure (line 72), RollbackToAsLatestProcedure (line 87) and Spark RollbackProcedure (line 116) cannot find branch tags. #9044 fixed the same pattern in StaticFromTagStartingScanner.

Are you willing to submit a PR?

• I'm willing to submit a PR!