Exercise 2: Three Small Inserts Landing on the Same Page — Possible Solution
====================================================================

THE TEST
------------------------------
    table = HeapTable(hf, Schema([('n', 'TEXT')]))
    ids = [table.insert([f"x{i}"]) for i in range(3)]

RESULT
------------------------------
    ids -> [(0, 0), (0, 1), (0, 2)]

All three row IDs share page_num == 0 -- three distinct slots (0, 1,
2) on the SAME page, not three separate pages.

WHICH PART OF insert() IS RESPONSIBLE
------------------------------
insert()'s own logic is:

    n = self.heap_file.num_pages()
    if n > 0:
        page = self.heap_file.read_page(n - 1)   # the LAST existing page
        try:
            slot = page.add_record(record)
            self.heap_file.write_page(n - 1, page)
            return (n - 1, slot)
        except ValueError:
            pass   # full -- fall through to allocating a new one
    page_num = self.heap_file.allocate_page()
    ...

For the FIRST insert, n (num_pages()) is 0, so the `if n > 0:` branch
is skipped entirely -- a new page (page 0) is allocated, and the
record goes into it, returning (0, 0).

For the SECOND insert, n is now 1 -- the `if n > 0:` branch runs,
reading page n-1 = page 0 (the same page the first record went into).
Since page 0 still has plenty of room for one more tiny record,
page.add_record() succeeds without raising ValueError, and the
function returns (0, 1) directly -- the `except ValueError: pass`
branch, and the subsequent allocate_page() call, are never reached at
all.

The THIRD insert follows the exact same path as the second: n is
still 1 (no new page was allocated for insert #2), page 0 is read
again, and the record fits again, giving (0, 2).

WHY THIS WORKS AS AN ANSWER
------------------------------
The specific mechanism responsible is the `if n > 0: ... try: ...
except ValueError: pass` structure -- insert() always attempts to
reuse the LAST page before ever considering a new one, and only falls
through to allocate_page() when that attempt genuinely raises
ValueError (meaning the last page really is full, per Chapter 3's own
capacity check). This is the direct fix for the wasteful "allocate a
new page for every single insert" alternative named in the chapter's
own "Where This Connects" table -- reusing existing space is the
default behavior, not an afterthought.