fix(ssh-gate): listen on the upstream port so URL-supplied ports work

Bug: git fetch failed with "connect to host
claude-bottle-ssh-gate-implementer port 30009: Connection refused".
OpenSSH treats a URL-supplied port (the user's remote was
ssh://git@gitea.dideric.is:30009/...) as overriding the
~/.ssh/config Port directive, so even though the config wrote
Port 30000 the agent dialed :30009 — where nothing was listening
because the gate had been assigned BASE_LISTEN_PORT + index.

Fix: the gate's listen port now equals the upstream port. Same
script, same socat, just port = entry.Port. Two entries on the
same upstream port are rejected at prepare time (the gate is one
container with a flat port space).

Re-smoked: probe nc github.com via the gate at :22, banner came
back as expected.

PRD 0007 updated to record the design refinement.

claude_bottle/ssh_gate.py

@@ -17,13 +17,11 @@ from abc import ABC, abstractmethod
 from dataclasses import dataclass
 from pathlib import Path
 
+from .log import die
 from .manifest import Bottle
 
-# First listen port on the gate; entry i listens on BASE_LISTEN_PORT + i.
-# Picked high enough to avoid colliding with anything an alpine image
-# might pre-bind. The port space is per-gate (gate is per-agent) so
-# collisions across bottles aren't possible.
-BASE_LISTEN_PORT = 30000
+# Default port when an ssh entry has no `Port` field. Matches OpenSSH.
+_DEFAULT_SSH_PORT = 22
 
 
 @dataclass(frozen=True)
@@ -32,7 +30,15 @@ class SSHGateUpstream:
     forward each connection to `upstream_host:upstream_port`. The
     `bottle_host_alias` is the `Host` value from the manifest entry,
     kept for diagnostics + so the ssh provisioner can correlate
-    upstreams with their alias."""
+    upstreams with their alias.
+
+    `listen_port` mirrors the upstream port. That choice lets git
+    URLs that bake the upstream port into the remote (e.g.
+    `ssh://git@host:30009/repo.git`) work without rewriting: OpenSSH
+    treats a URL-supplied port as overriding the config's `Port`
+    directive, so the gate must be reachable on the same port the URL
+    names. Two ssh entries that share an upstream port are a config
+    error and rejected at prepare time."""
 
     listen_port: int
     upstream_host: str
@@ -60,19 +66,33 @@ class SSHGatePlan:
 
 
 def ssh_gate_upstreams_for_bottle(bottle: Bottle) -> tuple[SSHGateUpstream, ...]:
-    """Deterministic assignment of listen ports to bottle.ssh entries:
-    BASE_LISTEN_PORT + index. Order matches `bottle.ssh` so a manifest
-    re-order yields a different port mapping (intentional — the
-    provisioner reads the same tuple)."""
-    return tuple(
-        SSHGateUpstream(
-            listen_port=BASE_LISTEN_PORT + i,
-            upstream_host=e.Hostname,
-            upstream_port=e.Port,
-            bottle_host_alias=e.Host,
+    """Build the gate's upstream table. Each ssh entry's listen port
+    equals its upstream port so URL-supplied ports (which override
+    `~/.ssh/config`'s `Port` directive) still reach the gate.
+
+    Dies on two entries sharing an upstream port — the gate is a
+    single container with a flat port space, so each listener has to
+    be unique."""
+    seen_ports: dict[int, str] = {}
+    upstreams: list[SSHGateUpstream] = []
+    for e in bottle.ssh:
+        port = int(e.Port) if e.Port else _DEFAULT_SSH_PORT
+        if port in seen_ports:
+            die(
+                f"ssh entries '{seen_ports[port]}' and '{e.Host}' share upstream port "
+                f"{port}; the per-agent ssh gate can only forward one upstream "
+                f"per port. Change one of the upstream Ports in claude-bottle.json."
+            )
+        seen_ports[port] = e.Host
+        upstreams.append(
+            SSHGateUpstream(
+                listen_port=port,
+                upstream_host=e.Hostname,
+                upstream_port=e.Port,
+                bottle_host_alias=e.Host,
+            )
         )
-        for i, e in enumerate(bottle.ssh)
-    )
+    return tuple(upstreams)
 
 
 def ssh_gate_render_entrypoint(upstreams: tuple[SSHGateUpstream, ...]) -> str:

docs/prds/0007-ssh-egress-gate.md

@@ -108,8 +108,14 @@ script that backgrounds N socat invocations:
 socat TCP-LISTEN:<port_i>,reuseaddr,fork TCP:<Hostname_i>:<Port_i>
 ```
 
-Listen ports are assigned deterministically per ssh entry (e.g.
-`30000 + index`). One container, N listeners, N upstreams.
+Listen ports mirror the upstream port (entry `Port`, default 22).
+That choice is load-bearing: OpenSSH treats a URL-supplied port
+(e.g. `ssh://git@host:30009/repo.git`) as overriding the config's
+`Port` directive, so the gate has to be reachable on the same port
+the URL names — otherwise git fetch hits "connection refused" on
+the URL's port even though the config block points elsewhere. Two
+ssh entries sharing an upstream port are a config error and
+rejected at prepare time. One container, N listeners, N upstreams.
 
 ### Existing code touched
 

tests/unit/test_ssh_gate.py

@@ -6,8 +6,8 @@ import tempfile
 import unittest
 from pathlib import Path
 
+from claude_bottle.manifest import Manifest
 from claude_bottle.ssh_gate import (
-    BASE_LISTEN_PORT,
     SSHGate,
     SSHGatePlan,
     SSHGateUpstream,
@@ -29,17 +29,20 @@ class _StubGate(SSHGate):
 
 
 class TestUpstreamAssignment(unittest.TestCase):
-    def test_indexed_listen_ports(self):
+    def test_listen_port_matches_upstream_port(self):
+        # Critical: URLs like ssh://git@host:30009/... override the
+        # config Port directive, so the gate must listen on the same
+        # port the URL names.
         bottle = fixture_with_ssh().bottles["dev"]
         upstreams = ssh_gate_upstreams_for_bottle(bottle)
         self.assertEqual(2, len(upstreams))
-        self.assertEqual(BASE_LISTEN_PORT, upstreams[0].listen_port)
-        self.assertEqual(BASE_LISTEN_PORT + 1, upstreams[1].listen_port)
+        # Fixture: tailscale-gitea -> 100.78.141.42:30009, github -> github.com:22.
+        self.assertEqual(30009, upstreams[0].listen_port)
+        self.assertEqual(22, upstreams[1].listen_port)
 
     def test_upstream_fields_mirror_ssh_entry(self):
         bottle = fixture_with_ssh().bottles["dev"]
         first = ssh_gate_upstreams_for_bottle(bottle)[0]
-        # The fixture's first ssh entry: tailscale-gitea / 100.78.141.42:30009.
         self.assertEqual("tailscale-gitea", first.bottle_host_alias)
         self.assertEqual("100.78.141.42", first.upstream_host)
         self.assertEqual("30009", first.upstream_port)
@@ -48,20 +51,40 @@ class TestUpstreamAssignment(unittest.TestCase):
         bottle = fixture_minimal().bottles["dev"]
         self.assertEqual((), ssh_gate_upstreams_for_bottle(bottle))
 
+    def test_duplicate_upstream_port_is_rejected(self):
+        # Two entries on the same upstream port can't both have a
+        # listener — the gate is one container with a flat port
+        # space. Surface as a clear config error.
+        manifest = Manifest.from_json_obj({
+            "bottles": {
+                "dev": {
+                    "ssh": [
+                        {"Host": "a", "IdentityFile": "/dev/null",
+                         "Hostname": "host-a.example", "User": "git", "Port": 22},
+                        {"Host": "b", "IdentityFile": "/dev/null",
+                         "Hostname": "host-b.example", "User": "git", "Port": 22},
+                    ],
+                }
+            },
+            "agents": {"demo": {"skills": [], "prompt": "", "bottle": "dev"}},
+        })
+        with self.assertRaises(SystemExit):
+            ssh_gate_upstreams_for_bottle(manifest.bottles["dev"])
+
 
 class TestEntrypointRender(unittest.TestCase):
     def test_one_socat_line_per_upstream(self):
         upstreams = (
-            SSHGateUpstream(30000, "gitea.example", "22", "gitea"),
-            SSHGateUpstream(30001, "github.com", "22", "gh"),
+            SSHGateUpstream(30009, "gitea.example", "30009", "gitea"),
+            SSHGateUpstream(22, "github.com", "22", "gh"),
         )
         script = ssh_gate_render_entrypoint(upstreams)
         self.assertIn("#!/bin/sh", script)
         self.assertIn(
-            "socat TCP-LISTEN:30000,reuseaddr,fork TCP:gitea.example:22 &", script
+            "socat TCP-LISTEN:30009,reuseaddr,fork TCP:gitea.example:30009 &", script
         )
         self.assertIn(
-            "socat TCP-LISTEN:30001,reuseaddr,fork TCP:github.com:22 &", script
+            "socat TCP-LISTEN:22,reuseaddr,fork TCP:github.com:22 &", script
         )
         # wait blocks the entrypoint so PID 1 stays alive while sockets
         # are open.