Should upsert() work with compound primary key?

[jclark-dot-org]

Given this table:

create table main.summary (
    Source      TEXT,
    Object      TEXT,
    Category    TEXT,
    Count       INTEGER,
    primary key (Source, Object, Category)
)

I'd like to have a simple helper to run rollups like so:

def summarize(db, table, source, object_name, category='All', criteria=None):
    db['summary'].upsert({
        'source': source,
        'object': object_name,
        'category': category,
        'count': table.count_where(criteria)
    })

To use like so:

utils.summarize(db, db["accounts_a"], 'Client A', 'Accounts')
utils.summarize(db, db["accounts_b"], 'Client B', 'Accounts', 'Customer', 'Type = "Customer"')
utils.summarize(db, db["accounts_b"], 'Client B', 'Accounts', 'Prospect', 'Type = "Prospect"')

But I'm getting an error that upsert requires a pk:

  File "/Users/jclark/Documents/dev/clientname/merge/scripts/utils.py", line 13, in summarize
    db['summary'].upsert({
  File "/opt/homebrew/lib/python3.12/site-packages/sqlite_utils/db.py", line 3346, in upsert
    return self.upsert_all(
           ^^^^^^^^^^^^^^^^
  File "/opt/homebrew/lib/python3.12/site-packages/sqlite_utils/db.py", line 3383, in upsert_all
    return self.insert_all(
           ^^^^^^^^^^^^^^^^
  File "/opt/homebrew/lib/python3.12/site-packages/sqlite_utils/db.py", line 3237, in insert_all
    raise PrimaryKeyRequired("upsert() requires a pk")
sqlite_utils.db.PrimaryKeyRequired: upsert() requires a pk

Per the upsert docs, the pk param to upsert() is only used when creating the target table, which I am not, so I'm assuming the error means it doesn't like my pk. Is that because it's a compound key? Or am I doing something else wrong?