memory-auto-split

Split an over-ceiling topic file that has no other automated reduction path. This is the gap /mempenny:memory-curate and /mempenny:memory-shard-roll leave open (docs/memory-taxonomy-design.md §2-§4b): curate never touches charter.md/pending.md (no ### entries, and distilling requirements or in-flight work is destructive — correctly so), and shard-roll never touches a year that hasn't fully closed ("no mid-year shards, ever" is shard-roll's own, deliberate pin). Before this command existed, an over-ceiling pending.md (or a log-topic stuck entirely in the open year) had no automatic reduction path at all and just grew forever until a human noticed — see docs/memory-taxonomy-design.md's §4b for the incident that motivated this.

The unifying principle: over ceiling → the main file becomes an INDEX, and the items it used to hold become PAGES the index points at. Three strategies below are three expressions of that one rule, chosen mechanically from what the file actually contains — never guessed, never an LLM judgment call — plus one last-resort fallback for content with no structure to index at all:

1. DATE (worklog/support/decisions) — the chronological expression. The parent's own ## Shards index block (Step 6, below) IS the index; the locked per-period shard files ARE the pages.
2. SUBJECT-INDEX (charter/pending, when ## -structured — the primary, real shape of a working pending.md) — the subject expression, and the most direct one: the live file itself becomes the index outright (frontmatter + preamble + one bullet per subject), and every top-level ## block becomes its own detail page.
3. PROSE-PEEL (charter/pending, only when neither of the above applies) — a last-resort positional split for genuinely structureless prose that still carries datestamps, no index/pages framing, just oldest-vs-newest.
4. Refuse closed — nothing to safely index, peel, or order; reported for manual trimming.

Unlike curate, this command makes no judgment call about content — it never decides what's worth keeping. It is pure, mechanical, content-preserving relocation. That is what makes it safe to run unattended, even on pending.md: nothing is distilled, archived-by-verdict, or deleted — every byte that leaves the live file is proven to still exist, verbatim, somewhere in the pages.

Step 1 — Parse arguments

The user invoked this command with: $ARGUMENTS

• First positional argument — absolute path to a topic file. Required.
• --lang <code> — output language. Default from MEMPENNY_LOCALE or en.

There is no --yes flag and no confirmation gate — see "Why no confirmation gate" under Constraints below; this matches /mempenny:memory-shard-roll, not /mempenny:memory-curate.