chore: ledgers merge by union; land the 2026-08-13 Muse Glimmer journal

[mazze93]

Lands the three journal commits that had been stranded at 3-ahead / 20-behind since 2026-08-13, plus the .gitattributes union rule that made the rebase tractable.

Why this was stuck

Two independent blockers, both now diagnosed:

1. add/add conflicts on all three journal files. The merge base had no docs/journal/; both sides created it independently. Nothing could fast-forward.
2. main requires verified signatures, and this machine has none. The account has zero SSH signing keys registered (GET /user/ssh_signing_keys returns empty). The local key exists and signs correctly — git log --format=%G? reports G on all four commits — but GitHub cannot verify it, so every commit reads Unverified and the ruleset rejects a direct push. A direct git push from this clone could never have succeeded, which is most of why these commits sat for three weeks. Squash-merging this PR sidesteps it, because the resulting commit is signed by GitHub.

Follow-up for the account owner, outside this PR: register ~/.ssh/id_ed25519.pub (titled "commit signing 2026-08-30", SHA256:u/YX5OMJo+IAT4nTNgydwknMkcuBwV0hf0buJNVvN7g) under Settings → SSH and GPG keys → Signing keys. Until that happens, every commit authored on this machine since 2026-08-30 is unverified across the whole fleet, not just here.

The union rule

.gitattributes marks docs/journal/DECISIONS.md as merge=union and deliberately marks CHECKPOINT.md and PLAN.md as -merge. The discrimination is the point: union is only safe for a ledger appended at the bottom and never edited above the last entry. CHECKPOINT.md is a projection that gets rewritten (union would duplicate checklist items and resurrect ticked boxes) and PLAN.md is edited in place.

Verified on this repo's own real divergence rather than a synthetic case:

file	rule	result
DECISIONS.md	merge=union	auto-merged, 437 lines = 395 upstream + 42 local, zero conflict markers, and zero lines lost from either side — verified by set-difference, not by eyeballing the diff
CHECKPOINT.md	-merge	conflicted as intended, hand-resolved
PLAN.md	-merge	conflicted as intended, hand-resolved

How the two conflicts were resolved

Chronologically, with both sides preserved verbatim. Upstream's content (the 2026-08-04 session) stays as the document body; the divergent branch's content (the 2026-08-13 Muse Glimmer session) is appended below an HTML-comment seam recording its provenance, with its H1 demoted to H2 so each file keeps exactly one top-level heading.

Line accounting: CHECKPOINT.md 68 + 25 + 9 seam = 102. PLAN.md 63 + 93 + 6 seam = 162. Nothing dropped.

One incidental change

.claude/settings.local.json was deleted upstream in #44 and is no longer tracked. A local modification to it existed in the working tree; this PR accepts the upstream untracking (git rm --cached) and leaves the file on disk. Note it is not in .gitignore, so it will keep reappearing as untracked — worth adding, separately.

Verification

• The rebase completed clean after the single hand-resolution; the two follow-on commits replayed with no further conflict.
• All four commits sign locally (%G? = G).
• No conflict markers anywhere under docs/journal/.
• Not checked by this PR: CI/CodeQL results (running now), and the 5 high Dependabot advisories currently open on main — pre-existing and unrelated to this change.