feat: add coldfront.drop_iceberg_table for decoupled and tiered tables

[vyruss]

Add a function to drop the Iceberg table behind the registered relation, in either mode, with an explicit purge decision and no default.

Decoupled: nothing remains.
Tiered: the cold tier goes and the hot table returns under its own name.
Plain DROP TABLE / DROP VIEW stays blocked.

Caveat: Table protection needs to be manually enabled for the table in Lakekeeper to prevent purging.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 18efb97a-2f0e-4abe-88f5-32b5f9a96915

📥 Commits

Reviewing files that changed from the base of the PR and between 6cc9ecd and b7d2909.

⛔ Files ignored due to path filters (1)

• extension/coldfront/test/expected/drop_iceberg_table.out is excluded by !**/*.out

📒 Files selected for processing (9)

• README.md
• ci/journey.sh
• docs/architecture.md
• docs/architecture_decoupled.md
• docs/index.md
• docs/usage.md
• extension/coldfront/Makefile
• extension/coldfront/coldfront--1.0.sql
• extension/coldfront/test/sql/drop_iceberg_table.sql

📝 Walkthrough

Walkthrough

Changes

Adds coldfront.drop_iceberg_table() with purge-aware Iceberg deletion, PostgreSQL and tiered-table teardown, regression and end-to-end tests, and documentation for both operating modes.

Iceberg drop implementation

Layer / File(s)	Summary
Drop and teardown workflow extension/coldfront/coldfront--1.0.sql	Adds SQL helpers for purge-aware DuckDB drops, PostgreSQL unregistration, tiered-table restoration, validation, claims, and execution.

Validation and integration

Layer / File(s)	Summary
Regression and journey coverage extension/coldfront/test/sql/drop_iceberg_table.sql, extension/coldfront/Makefile, ci/journey.sh	Tests decoupled and tiered cleanup, purge variants, identifier quoting, catalog state, PostgreSQL state, and Lakekeeper object behavior.

Documentation

Layer / File(s)	Summary
Supported drop workflow README.md, docs/index.md, docs/usage.md, docs/architecture.md, docs/architecture_decoupled.md	Documents the function, purge semantics, mode-specific teardown, blocked direct drops, and asynchronous cleanup.

Estimated code review effort: 4 (Complex) | ~45 minutes

Suggested reviewers: dpage

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly names the new drop_iceberg_table feature and its decoupled/tiered scope.
Description check	✅ Passed	The description matches the change by explaining the drop behavior, modes, and purge caveat.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/drop-iceberg-table

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

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[coderabbitai]

Actionable comments posted: 3

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/architecture_decoupled.md`:
- Around line 301-309: Update the purge behavior description in the architecture
documentation to clarify that the hard profile provides no recovery window while
physical object deletion still occurs asynchronously through Lakekeeper’s
background purge process. Replace “immediate” wording with language
distinguishing logical irrecoverability from eventual physical deletion, and
preserve the soft-profile expiration-window behavior.

In `@docs/usage.md`:
- Around line 352-362: Update the purge workflow documentation to state that
Lakekeeper table protection must be enabled manually before recommending
purge=true, and clarify that this function cannot override an active protection
hold. Keep the existing explanation of the irreversible purge outcomes and
asynchronous deletion behavior unchanged.

In `@extension/coldfront/coldfront--1.0.sql`:
- Around line 2464-2476: Update the alias construction in the DROP TABLE
statement’s `v_alias` expression to include a stable digest derived from the
current `coldfront.warehouse`, `coldfront.lakekeeper_endpoint`, and
`_attach_delegation_mode()` values, while retaining the purge-state distinction.
Ensure the resulting alias remains valid for the existing `%I` identifier
formatting and changes whenever any catalog setting changes.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 7effb807-d3c9-4882-8a56-ff6bc6bf8f4a

📥 Commits

Reviewing files that changed from the base of the PR and between 85baec5 and 6cc9ecd.

⛔ Files ignored due to path filters (1)

• extension/coldfront/test/expected/drop_iceberg_table.out is excluded by !**/*.out

📒 Files selected for processing (9)

• README.md
• ci/journey.sh
• docs/architecture.md
• docs/architecture_decoupled.md
• docs/index.md
• docs/usage.md
• extension/coldfront/Makefile
• extension/coldfront/coldfront--1.0.sql
• extension/coldfront/test/sql/drop_iceberg_table.sql