ALTER COLLECTION x ADD COLUMN y rejected — router dispatcher missing branch

[hollanf]

Summary

ALTER COLLECTION x ADD COLUMN y ... is documented but rejected at parse time. The underlying handler exists — the router just doesn't dispatch to it for ALTER COLLECTION.

Zero-downtime schema evolution impossible on strict collections. Only workaround is DROP + CREATE + re-ingest (data loss unless caller has their own backup tooling).

Repro

CREATE COLLECTION memories TYPE DOCUMENT STRICT (
  id STRING PRIMARY KEY,
  name STRING NOT NULL
);

ALTER COLLECTION memories ADD COLUMN is_latest BOOL DEFAULT true;

Error:

parse error: sql parser error: Expected: one of VIEW or TYPE or TABLE or INDEX

Same error for every column type / default combination. ALTER TABLE memories ADD COLUMN is_latest BOOL DEFAULT true works on the same collection.

Expected

Per docs/documents.md:131:

ALTER COLLECTION orders ADD COLUMN region STRING DEFAULT 'us-east';

Root cause — dispatcher asymmetry

In src/control/server/pgwire/ddl/router/schema.rs:

• Line 84 wires ALTER TABLE ... ADD COLUMN → alter_table_add_column()
• Lines 103–136 wire ALTER COLLECTION ... for OWNER, SET RETENTION, LAST_VALUE_CACHE, LEGAL_HOLD, SET APPEND_ONLY
• No branch for ALTER COLLECTION ... ADD COLUMN

Statement falls through to DataFusion's sqlparser-rs, which only knows ALTER {TABLE,VIEW,TYPE,INDEX} — hence the misleading error list.

Handler at src/control/server/pgwire/ddl/collection/alter.rs:14-104 is already catalog-generic, so it would work for collections if the router reached it.

Special case ALTER COLLECTION ... ADD COLUMN ... AS MATERIALIZED_SUM is wired separately at router/collaborative.rs:58-63 — plain ADD COLUMN fell through the cracks.

Tests

tests/sql_transactions.rs:71-76 covers ALTER TABLE ... ADD COLUMN only. No test exercises the documented ALTER COLLECTION ... ADD COLUMN path.

Pointers

• `src/control/server/pgwire/ddl/router/schema.rs:84`
• `src/control/server/pgwire/ddl/router/schema.rs:103-136`
• `src/control/server/pgwire/ddl/router/collaborative.rs:58-63`
• `src/control/server/pgwire/ddl/collection/alter.rs:14-104`
• `docs/documents.md:131`
• `tests/sql_transactions.rs:71-76`