chore(tiering): remove dead read_parquet query builders

[xe-nvdk]

Follow-up to #501.

Summary

Removes four dead functions from internal/tiering/router.go:

• BuildReadParquetExpr, BuildMultiTierQuery (exported, never called)
• buildReadParquet, buildFullPath (helpers, only called by the above)

These have had zero callers since they were introduced in the original 2-tier commit (2575746). The query engine builds tiered read_parquet() calls inline in internal/api/query.go (buildMultiTierReadParquet → quotePath) and never routes through these builders. The only live router methods — GetStoragePathsForQuery, GetGlobPathsForQuery (the one query.go actually calls), and getBackendName — are untouched.

Why delete rather than keep

#501 had just escaped and nil-guarded these as defense-in-depth. But once confirmed unreachable (exhaustive cross-repo reference search: the four functions referenced only each other + their tests; verified GetGlobPathsForQuery, the live entry point, calls none of them), deleting is the better outcome:

• Less surface to maintain.
• Removes the raw-whereClause SQL-fragment injection sink that BuildMultiTierQuery carried (documented in fix(tiering): escape paths in router read_parquet builders (#307) #501 as a hazard for any future caller — now moot).

They are not pending/incomplete scaffolding: an earlier hot/warm/cold design was collapsed to 2-tier before this code landed (tier_test.go comments: "Warm tier removed in 2-tier system"; TierWarm was never a committed constant), and router.go was born in the 2-tier commit itself. This is superseded code, safe to remove.

Drops the now-unused sqlutil, storage, and strings imports. Pure deletion (241 lines), no behavior change, no release-notes entry.

Test plan

• go build ./cmd/... ./internal/...
• go vet ./internal/tiering/, gofmt -l clean
• go test ./internal/tiering/ ./internal/api/ -count=1 passes

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request removes several unused methods (BuildReadParquetExpr, BuildMultiTierQuery, buildReadParquet, and buildFullPath) and their associated imports from internal/tiering/router.go. It also deletes the corresponding unit tests that validated these methods. There are no review comments to address, and I have no additional feedback to provide.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[gemini-code-assist]

Code Review

This pull request removes unused and unwired query-building methods (BuildReadParquetExpr, BuildMultiTierQuery, buildReadParquet, and buildFullPath) from the tiering package, along with their associated unit tests and unused imports. I have no feedback to provide.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.