feat(ol_dbt_cli): add ol-dbt local snapshot and raw-relation support to ol-dbt diff

[rachellougee]

What are the relevant tickets?

#2407

Description (What does it do?)

Adds a new companion command for local dbt development, plus support in ol-dbt diff for comparing against it:

• ol-dbt local snapshot: save a model's current build under a new name, so you can easily compare it against itself before and after a code change.
• ol-dbt diff --old-raw/--new-raw (plus --old-schema/--new-schema/--old-database/--new-database): compare against an already-materialized table — like a snapshot, or a copy sitting in another schema/database — instead of only a live dbt model.

Useful for validating and fixing bugs in how a report joins its dimensional tables — used to find and fix the remaining bugs in enrollment_detail_report see #2468

Test plan

• pytest src/ol_dbt_cli/tests/ — 389 passed
• ruff check / ruff format / mypy — clean
• ol-dbt local snapshot used in practice to validate the enrollment_detail_report fixes in fix(enrollment_detail_report): fix two join fan-out bugs  #2468

How can this be tested?

Verifies ol-dbt local snapshot + ol-dbt diff --old-raw correctly isolate a code change from production drift

1. cd src/ol_dbt
2. Register a model's Glue tables and build it locally:

ol-dbt local setup    # one-time bootstrap for the local DuckDB+Iceberg dev environment                                                                                                   
ol-dbt local register --database ol_warehouse_production_dimensional                                                                                           
ol-dbt run --select dim_user --target dev_local        

3. Snapshot the current build as a frozen baseline: ol-dbt local snapshot dim_user --as dim_user_baseline
4. With no code change yet, diff the baseline against the live model — should show a clean match, confirming the round trip is precise:
   ol-dbt diff --target dev_local --old dim_user_baseline --old-raw --new dim_user --primary-key user_pk
5. Expected: MATCH ... row Δ 0, 0 column mismatch(es).
6. Make a real code change to dim_user.sql, then rebuild: ol-dbt run --select dim_user --target dev_local
7. Re-run the same diff from step 4 — any mismatch now reported is attributable only to the code change, since both sides are built from the same underlying data pull.

  Verified real output (step 4, no change made):                                                                                                                 
  MATCH  dim_user_baseline (raw) → dim_user  (dev_local)                                                                                                         
     Compared columns: 48                                                                                                                                        
     Row counts: dim_user_baseline (raw)=7549738  dim_user=7549738  Δ=0                                                                                          
  Summary: match — row Δ 0, 0 column mismatch(es).                                                                                                               

Additional Context

[github-actions]

🔎 ol-dbt impact — column-level blast radius

✅ No column-level downstream impact detected for the changed models.

_{Posted by ol-dbt impact (annotate-only — does not block merge).}

[Copilot]

Pull request overview

Adds local-development tooling to make dbt model changes easier to validate by enabling “before/after” baselines and allowing ol-dbt diff to compare against already-materialized relations (not only manifest-resolved ref() models). This supports safer dimensional/mart migrations by making row/column-level comparisons against production-derived data practical and repeatable.

Changes:

• Add ol-dbt local snapshot to materialize a model’s current build under a new table name for baseline comparisons.
• Extend ol-dbt diff with --old-raw/--new-raw plus schema/database overrides to diff against literal relations, and improve mismatch output formatting.
• Expand CLI documentation and tests to cover snapshotting, raw relation resolution, and labeling/output behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/ol_dbt/README.md	Documents workflows for using ol-dbt diff together with ol-dbt local snapshot, including raw-relation comparisons across schemas.
src/ol_dbt_cli/ol_dbt_cli/commands/local_dev.py	Adds the local snapshot command that CTAS-copies a model build to a baseline table.
src/ol_dbt_cli/ol_dbt_cli/commands/diff.py	Adds raw-relation support (Relation.create), schema/database overrides, improved per-column query generation, and clearer mismatch formatting/labels.
src/ol_dbt_cli/tests/test_local_dev.py	Adds unit tests validating snapshot SQL construction and identifier validation.
src/ol_dbt_cli/tests/test_diff.py	Adds extensive coverage for raw relation handling, relation Jinja rendering, sample mismatch formatting, labels, and JSON schema updates.

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