[BugFix] FSE-v2 missed setting the schema for shared-data sorted schema change (backport #72235)

[mergify]

Why I'm doing:

On shared-data, an ALTER that changes the sort key is wrongly cancelled
with a misleading "table not found" when the schema cache is disabled:

update information_schema.be_configs
    set value = "0" where name = "lake_metadata_cache_limit";

ALTER TABLE t1 ADD COLUMN k0 INT KEY DEFAULT "0" FIRST;

W table_schema_service.cpp:333 failed to get schema.
  db_id: 0, table_id: 0, schema_id: 10422, tablet_id: 10423, txn_id: 249,
  error: Table not exist: table not found, may be dropped, db id: 0, table id: 0

Walking the cause:

• This alter runs through SortedSchemaChange, which writes the converted
  rowsets through DeltaWriter. The builder is only fed schema_id; the
  writer is left to resolve the schema itself.

• Since [Enhancement] Add BE TableSchemaService for Fast Schema Evolution in shared-data #66699 (FSE-v2 in shared-data, merged Dec 2025), DeltaWriter
  resolves the schema through TableSchemaService, whose lookup chain is:

  schema cache (by schema_id)
     -> latest cached tablet metadata
     -> FE RPC (by db_id, table_id, schema_id)
  

• Shared-data alter tasks (TAlterTabletReqV2) don't carry catalog ids.
  When the lookup falls through to the RPC, the request goes out with
  db_id=0, table_id=0 and FE rightly answers "Table not exist".

The bug has been latent because the cache (default 2 GB) and cached
tablet metadata almost always answer the schema lookup before the RPC.
Disabling the cache exposes the broken RPC path.

DirectSchemaChange is unaffected — it builds its writer with a
TabletSchemaPtr directly and never touches the service.

What I'm doing:

The sorted schema change already holds the new tablet schema; the
schema-service lookup is unnecessary. Hand the schema to DeltaWriter
directly.

• DeltaWriterBuilder gains set_tablet_schema(TabletSchemaPtr). When
  set, DeltaWriter::init_tablet_schema() short-circuits and bypasses
  TableSchemaService entirely. set_schema_id is still required and
  validated against the preset schema's id.
• SortedSchemaChange::process passes the new tablet schema into the
  builder. DirectSchemaChange is unchanged.

As a side effect this also removes one (normally successful) RPC per
sorted schema change in the cache-hit case — the residual TODO already
flagged in schema_change.cpp.

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
  • BE UT: a regression test that disables the metacache, hooks the
    schema RPC sync point, and asserts the sorted schema change runs
    end-to-end without firing the RPC.
  • SQL: test_fse_alter_with_metacache_off @cloud pinning the original
    repro.
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
  • This pr needs auto generate documentation
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.1
  • 4.0
  • 3.5
  • 3.4

    ---

    This is an automatic backport of pull request [BugFix] FSE-v2 missed setting the schema for shared-data sorted schema change #72235 done by Mergify.

[mergify]

Cherry-pick of d70921f has failed:

On branch mergify/bp/branch-4.0/pr-72235
Your branch is up to date with 'origin/branch-4.0'.

You are currently cherry-picking commit d70921f1e4.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   be/src/storage/lake/delta_writer.cpp
	modified:   be/src/storage/lake/delta_writer.h
	modified:   be/src/storage/lake/schema_change.cpp
	new file:   test/sql/test_fast_schema_evolution/R/test_fse_alter_with_metacache_off
	new file:   test/sql/test_fast_schema_evolution/T/test_fse_alter_with_metacache_off

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   be/test/storage/lake/schema_change_test.cpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

@mergify[bot]: Backport conflict, please reslove the conflict and resubmit the pr