docs: add guide for updating git dependencies in Cargo

- Add new how-to guide covering hash updates for git dependencies
- Applies to any git dependency (e.g., nostr-sdk fork)
- Add critical note in AGENTS.md linking to this guide
- Emphasize that hash updates in both flake.nix and nix/module.nix are MANDATORY

1 files changed, 1 insertions, 0 deletions

diff --git a/AGENTS.md b/AGENTS.md
index 9b480b4..ef45a52 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -272,6 +272,7 @@ This was a key learning from GRASP-01: docs described plans, not implementation,
 6. **Archive naming:** Use `YYYY-MM-DD-description.md` format
 7. **test-ngit-relay.sh tests ngit-relay**: This script tests the reference implementation, NOT ngit-grasp
 8. **Configuration sync:** Config changes MUST be updated in all four places: `src/config.rs`, `docs/reference/configuration.md`, `nix/module.nix`, AND `.env.example`
+9. **Git dependencies:** When updating `Cargo.toml` or `Cargo.lock` with ANY git dependency (not crates.io), you MUST update hashes in BOTH `flake.nix` and `nix/module.nix`. See [docs/how-to/update-git-dependencies.md](docs/how-to/update-git-dependencies.md) - this is MANDATORY and builds will fail if skipped
 
 ## File Restrictions by Mode