Prove chunked result assembly end to end through Genie

[ivanvyd]

Chunked result assembly (ADR 0004)
is verified in both halves, but never as one flow.

What is already proven, live

• A Genie-executed statement's chunks are readable with the caller's own identity — HTTP 200 on
  both /api/2.0/sql/statements/{id} and .../result/chunks/0. This was the unknown ADR 0004
  shipped with.
• The wire contract behaves as the client assumes: on a deliberately chunked statement,
  total_chunk_count: 2, manifest.truncated: false, a workspace-relative
  next_chunk_internal_link, and following it returned the remainder with the row counts summing
  exactly to total_row_count.

What is not proven

Genie itself emitting a multi-chunk result. The Agent used for verification has a six-row
table, and Genie bounds its own SQL, so the composition of those two halves has never run.

Why it is not just "make a big table"

The demo Agent's table is also the fixture for the 9 live integration tests, which assert its exact
regions and totals. Enlarging it breaks them. Closing this needs a separate large table added
to a Genie Agent, which is a Genie Workbench configuration change.

What closing this looks like

1. Create a table with enough rows that a full read exceeds one chunk — roughly 40,000+ rows, since
   a chunk observed live held about 41,000.
2. Add it to a Genie Agent.
3. Ask for all of it, and check truncated is false with the full row count:
   lakespeak ask --agent <agent> --format json "show every row of <table>"
4. Record the outcome in docs/compatibility.md.

A negative result is a real result. If Genie always bounds its own SQL and never emits more
than one chunk, that is worth recording — it would mean this code path is unreachable in practice,
which changes how much it deserves to exist.