GitRepoSource walks the working tree at HEAD via `git ls-tree` + `git show`,
yielding one Document per text file. URI shape `git://<repo>/file/<path>`
intentionally omits the commit hash — re-ingest after new commits produces
fresh document_roots that aborist's prior-doc detection chains via
`supersedes` edges, so the audit trail and Merkle tree grow as the repo
grows. Binaries skipped via NUL-byte + UTF-8 decode probes; >5 MB files
filtered out by default. Commit hash + timestamp + subject ride along in
`extra` (informational only; not part of the Merkle commitment).
MercurialRepoSource mirrors via `hg manifest` + `hg cat`. Same supersedes
semantics, same shape.
Makefile adds:
make ingest-self (this repo -> aborist-self.db)
make ingest-git GIT_REPO=/path/to/repo (arbitrary git clone)
make ingest-hg HG_REPO=/path/to/repo (mercurial)
Each lands in its own shard file alongside existing shards/grok.db,
keeping per-shard write paths independent of the wikipedia 4-way ingest's
WAL writer lock.
