Boolean values differ between replication and query paths: "t"/"f" vs "true"/"false"

[alco]

Description

Boolean column values are represented differently depending on the response path:

• Replication path (changes_only): booleans are serialized as "t" and "f"
• Query path (full and subset): booleans are serialized as "true" and "false"

This inconsistency means clients cannot rely on a single boolean representation across all Electric response types.

Root cause

The replication path receives column values as-is from Postgres logical replication, which uses the single-character text output format for booleans (t/f).

The query path uses column::text in SQL (via pg_cast_column_to_text/1 in querying.ex), which produces the full words true/false.

These are both valid Postgres text representations of bool, but they differ.

Reproduction

1. Create a table with a boolean column:

   CREATE TABLE todos (id TEXT PRIMARY KEY, completed BOOLEAN DEFAULT false, title TEXT);

2. Insert a row:

   INSERT INTO todos (id, completed, title) VALUES ('1', true, 'test');

3. Compare responses:
   • changes_only response: "completed": "t"
   • full response: "completed": "true"
   • subset response: "completed": "true"

Expected behavior

Boolean values should be represented consistently across all response types (changes_only, full, subset).

Actual behavior

changes_only returns "t"/"f", while full and subset return "true"/"false".

Context

Originally reported as part of #4039. The char(n) padding inconsistency was fixed in #4044, but the boolean mismatch was intentionally left out of scope.

The fix in #4044 used concat(col, '') for bpchar to avoid affecting booleans — concat(bool_col, '') would produce t/f, which would have made the query path match replication but would be a breaking change for existing clients consuming "true"/"false" from snapshots.

Considerations

The fix needs to decide which representation is canonical:

• "true"/"false" (current query path) — more readable, what most clients likely expect
• "t"/"f" (current replication path) — Postgres native text output

If "true"/"false" is chosen as canonical, the replication path would need to normalize boolean values before storing/serving them. If "t"/"f" is chosen, the query path SQL would need adjustment (and this would be a breaking change for snapshot consumers).

[MdSadiqMd]

Hey @alco can I work on this?