Tailcat upstream snapshot

This directory vendors the networking core of tailscale/tailcat at commit c04c5afee401df40e620db8ae108e957ae07bcd9 (2026-08-27).

Imported upstream files:

• LICENSE
• disco.go
• pickregion.go
• pickregion_js.go
• tailcat.go
• wire.go
• export_test.go
• tailcat_test.go
• wire_test.go

The CLI, SSH support, README embedding, web demo, image, Nix files, module files, and repository configuration are intentionally omitted. Croc uses the Tailcat networking and wire layers directly and does not expose Tailcat's standalone wire protocol.

Croc-local changes

• tailcat.go: Server.StartContext is a minimal variant of Server.Start that lets croc's coordinated 30-second setup deadline cancel DERP-map discovery. Start retains upstream behavior by calling it with a background context. Its package overview omits the standalone Tailcat SSH-server claim, because croc does not import that CLI integration.
• croc_authorization.go: exposes the deterministic Tailcat address for a node key so croc can bind an authenticated invitation role to its tunnel source, and adds Server.RemoveAllowedClient so one-time client keys can be revoked.
• croc_status.go: adds a client status accessor for direct/DERP path transitions and final byte reporting.

All other imported source and test files are unchanged. SOURCE_HASHES.sha256 records SHA-256 hashes of the exact upstream files before the local patch. The resulting croc-patched tailcat.go has SHA-256 897b2a9a03be97cbd5a55009b158b4a54cd161cc0552438574dbc52e277718bd.

Croc deliberately uses stable tailscale.com v1.102.3 instead of Tailcat's pre-release Tailscale pseudo-version. The complete imported upstream test suite passes with that stable release. The gVisor version remains Tailcat's pinned v0.0.0-20260224225140-573d5e7127a8.

Updating

1. Select and record an immutable upstream Tailcat commit.
2. Download the source archive and verify its commit identity.
3. Re-copy only the files listed above, preserving LICENSE.
4. Regenerate SOURCE_HASHES.sha256 from the unmodified upstream files.
5. Reapply and review the documented Server.StartContext and package-comment changes, and keep croc-only additions in croc_*.go where possible.
6. Run go test ./internal/tailcat ./src/tailcattransport, the focused race tests, go test ./..., and croc's release cross-build matrix.