fix: derive every repo's spelling join from the body map

[Jammy2211]

Closes #287. Mind half: PyAutoLabs/PyAutoMind#333 (merge that first; this does not block on it — see the fallback below).

The defect, reproduced on main

The bare and prefixed spellings of seven repos normalised to two different keys, so a policy map filed under one was invisible to the other. _target_sets registered BOTH spellings of every PyAuto* repo as a known target while repo_aliases only joined them for the libraries:

mention	before	after
@PyAutoBrain	pyautobrain → PyAutoBrain/tests	unchanged
@autobrain	autobrain → no witness row	pyautobrain → PyAutoBrain/tests

So pyauto-brain refactor reported [unwitnessed: autobrain] and advised "strengthen tests first" for the best-tested repo in the organism, and pyauto-brain intake on the same mention filed Target: autobrain — a folder that does not exist. Five organs, one project repo and the Hands were split this way. Nothing failed; the advice was just quietly wrong.

The decision, taken before the edit

The prompt required answering the keying question first rather than sweeping aliases blind. Organs key on the PREFIXED form. That is not a new rule — it is #269's rule made executable: the canonical key is the package the repo SHIPS where it ships one, and the repo name where it does not. Organs ship no package; Nerves is the one that does and keys bare (autonerves) already. Everything downstream was filed prefixed for organs — test_witness, target_signals, REPO_DISPLAY, target_default_wiki, and the Mind's own target folders — so keying bare would have rekeyed five maps for no gain.

The class, not the fourth instance

repo_aliases was hand-maintained while the known-target set was derived from the body map, so the two drifted silently. The join is now derived (_derived_aliases), keyed off the body map's new package: field, and a hand row that contradicts the derivation raises instead of quietly winning. What stays hand-written is only what a body map cannot know: short forms (aa, af) and pre-rename spellings.

Two things found that were not in the prompt

• PyAutoScientist split the same way — joined.
• pyautolabs.github.io is now deliberately NOT registered. normalise_repo truncates at the first .//, so no mention could ever reach it. The tempting fix — alias the truncated head — is worse than the gap: that head is the org's own name, so @PyAutoLabs/PyAutoFit would have started resolving to the static site instead of PyAutoFit. The acceptance criterion's other branch ("or is deliberately not registered") covers it, and the exclusion is derived from the names, not a hand-kept list. A guard pins both halves.

REPO_DISPLAY also derives from the body map now — it had the beginnings of the same drift, with reachable keys carrying no row, so a header came out as Target: pyautohands.

Guards

Five, each mutation-tested rather than assumed:

Guard	Mutation that proves it
no repo splits across two keys	removing the derived join names all seven affected repos
no alias points at a key nothing is filed under	—
body map package: agrees with the witness map	mis-keying one package: value raises at import
unreachable repos excluded and their truncated head resolves to nothing	forcing the dotted repo back into the set
canonical keys survive a body map with no package:	deleting the fallback rows

That last one matters for merge order: CI checks the sibling Mind out at main, pinned, so a Brain half that required the Mind half would sit red until Mind merged. canonical_key falls back to the hand table's library rows when no package: is declared, giving identical keys either way. Those rows become dead weight once PyAutoMind#333 lands and can be deleted then.

Validation

• 515 tests pass (510 before).
• repos_sync --check all 13 legs OK. The tenant firewall rejected two drafts of this prose for naming instance repos, which is why the comments read generically — the same check that caught drafts at fix: retire PyAutoConf rename leftovers in Brain functional surfaces #267 and fix: witness map misses 5 repos with real test suites, splits 2 more across keys #269.
• A/B over every spelling in the alias table and target sets: exactly six resolutions changed, all of them the intended joins. Libraries, short forms, renames, workspaces and org-qualified paths are byte-identical.
• Heart NOT EVALUATED — pyauto-heart is unreachable from a web-github session, so leg 4 of the ship gate did not run. Recorded that way rather than claimed clean.

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