feat(gateway): mandatory identity-token attribution on every data plane (PR #354 review)

Codex review: the /31 TAP doesn't make source IP unspoofable, and the
app-layer token was returned by launch but never delivered or enforced, so
a spoofed source could select a victim bottle's policy/tokens. Make the
token mandatory and deliver it on each attributed plane (anti-spoof landed
separately as the network boundary).

Enforcement (control plane):
- `Orchestrator.resolve` now requires a matching (source_ip, identity_token)
  pair (constant-time) — no source-IP-only fallback. `/resolve` fail-closes
  (403) on a missing/empty/mismatched token.

Delivery, per plane (the token is `token_urlsafe`, safe in a URL):
- egress: proxy credentials (`HTTPS_PROXY=http://bottle:<token>@gw`). The
  addon reads `Proxy-Authorization` — from the request (HTTP) or captured at
  the CONNECT for HTTPS tunnels (keyed by client conn, cleared on disconnect)
  — validates, and strips it (+ the legacy header) before upstream.
- git-http: a URL-scoped `http.<gate>/.extraHeader: x-bot-bottle-identity`
  in the agent's git config (only over the http transport).
- supervise: `mcp add --header x-bot-bottle-identity: <token>` (claude +
  codex); the server reads the header and passes it to resolve.

Wiring: thread `ctx.identity_token` onto the firecracker + docker plans and
into the agent env/config at launch.

Verified on a KVM host: egress with the correct proxy-cred token returns
200 (HTTP and HTTPS/CONNECT), and no-token / wrong-token return 403; a real
`cli.py start --backend=firecracker` launch provisions git config + the
supervise MCP header and reaches the agent session, all under mandatory
enforcement. Fixed a `claude mcp add` arg-order bug (--header must follow
the positional name/url) found by that launch.

Transparent proxy for tools that ignore proxy env is deferred to a
follow-up (see thread); anti-spoof + host firewall remain the fail-closed
boundary.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

tests/unit/test_git_gate_render_provision.py

@@ -74,6 +74,19 @@ class TestRenderGitconfig(unittest.TestCase):
         out = git_gate_render_gitconfig((_entry(),), "1.2.3.4:9418", scheme="http")
         self.assertIn('[url "http://1.2.3.4:9418/repo.git"]', out)
 
+    def test_identity_token_extraheader_over_http(self) -> None:
+        # Delivered as a URL-scoped http.extraHeader so git-http can enforce
+        # the mandatory (source_ip, token) pair; only over the http transport.
+        out = git_gate_render_gitconfig(
+            (_entry(),), "1.2.3.4:9420", scheme="http", identity_token="TOK123")
+        self.assertIn('[http "http://1.2.3.4:9420/"]', out)
+        self.assertIn("extraHeader = x-bot-bottle-identity: TOK123", out)
+
+    def test_identity_token_omitted_over_git_scheme(self) -> None:
+        out = git_gate_render_gitconfig(
+            (_entry(),), "git-gate", scheme="git", identity_token="TOK123")
+        self.assertNotIn("extraHeader", out)
+
     def test_remote_key_alias_with_nondefault_port(self) -> None:
         out = git_gate_render_gitconfig(
             (_entry(RemoteKey="10.0.0.5", UpstreamPort="2222"),), "git-gate",