GENESIS: git mark init reads nostr.voucher to seed the first gitmark.txo

[melvincarvalho]

Re-scoped against the funding contract — see FUNDING.md (#43, PR #44). The original framing ("auto-discover base-key funding from .well-known/txo/txo.json") was reaching for the publish-mode artifact; the contract gives a cleaner seam.

The seam (per the contract)

nostr.voucher (bootstrap, written by fund-agent) and gitmark.txo (the running tip, gitmark-managed) are two distinct roles. They meet at exactly one point:

git mark init (GENESIS) reads nostr.voucher, sweeps it onto the repo's own key, and seeds the first gitmark.txo.

After that gitmark owns the tip; the voucher is spent and never re-read.

What to implement

• On git mark init, if gitmark.txo is unset, read git config --local nostr.voucher (a bearer txo:…?…&key= URI), sweep it to the repo's own key, and write the resulting output to gitmark.txo.
• If no nostr.voucher and no gitmark.txo: unfunded — print the base address to fund (current behaviour).
• --voucher <uri|file> stays as the explicit override for the same sweep.

Not this

• Reading .well-known/txo/txo.json is publish-mode only convenience, not the default path. The default handoff is the nostr.voucher config field.
• No dependence on fund-agent's internal namespace beyond the agreed nostr.voucher field.

Depends on

• Write nostr.voucher (bootstrap handoff) when funding a repo blocktrails/fund-agent#1 (producer writes nostr.voucher).
• Contract: Define the funding & state contract: clean-by-default, two roles (nostr.voucher bootstrap → gitmark.txo tip) #43 / PR docs: FUNDING.md — the funding & state contract #44.

Symptom this fixes

Funding a repo then git mark → No funding. Run: git mark init --voucher txo:..., because nothing bridged the funded output into gitmark.txo. With this, GENESIS does the bridge automatically.