Style

Code Style

Use raise exception, not assert. Using assert would be nice, but "ASSERT is meant for detecting program bugs, not for reporting ordinary error conditions", and can be disabled via plpgsql.check_asserts.
Whe possible, use a begin ... exceptions block to catch and re-raise exceptions, instead of checking for things that constraints already enforce, for much speed.

Use plural names for set-returning functions.
"public" functions (ones the user might call from the psql prompt or their code) typically take human-readable text arguments, e.g. repository name instead of repository id.

select get_tracked_rows('io.my_repo');

"private" functions begin with a underscore, and typically take ids where applicable.

select _get_tracked_rows('01939312-8f21-7243-8bc8-e6b0e9352cf9');

"public" functions do error checking for things like repository existence, and meaningful error messages. "private" functions just blow up.
Functions should start with the action being taken, e.g. create_repository() instead of repository_create().
Functions that fetch values and don't change state should start with:
- _get_loot() for functions that return vars and setof
- _is_funkty() for booleans
Macro-ops (e.g. stage_tracked_rows(), track_untracked_rows() don't do all the sanity and error checking that single-op functions do, because they rely on internal logic that is expected to be consistent. Speeds.
Prefer returns setof to returns table, setof is inlinable where table is not?
Type signatures look like this:

create or replace function foo( x int, y int, z decimal ) returns x as $$
$$ language plpgsql;

When arguments collide with column names (e.g. repository_id), prefix the argument with a underscore (e.g. _repository_id)

Core .sql source is in the root
Tests are in ./test
- test/unit is for coverage of every function
- test/shakespeare is for performance testing