Migrate SSH environment callback to bridge (#5116)

> **Stacked PR (part 3 of 7).** Depends on:
  - PR #5114
  - PR #5115
> Diff against `master` includes commits from earlier PRs in the stack —
the new commit in this PR is the topmost one.

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - Agents executing on a remote SSH-backed environment need a way to
call back into
>   the Paperclip control plane (run events, log streaming, signals)
> - When the SSH host can't reach the Paperclip host (NAT, firewalls, or
simply not
> on the same network), the run silently fails or hangs — a recurring
class of
>   failure during SSH testing
> - In sandboxed environments we already solved this with a callback
bridge that
> tunnels back through the existing connection; SSH was the odd one out
> - This PR migrates SSH execution to use the same callback bridge, so
every
> adapter's remote run uses one consistent reverse-channel. Per-adapter
SSH glue
> is deleted in favour of a shared `CommandManagedRuntimeRunner` built
from the
>   SSH spec
> - The benefit is fewer SSH-specific failure modes, a smaller code
surface, and
>   one place to evolve the callback contract going forward

## What Changed

- Added `createSshCommandManagedRuntimeRunner` in
`packages/adapter-utils/src/ssh.ts` that adapts an SSH spec into a
generic
  command-managed-runtime runner (with cwd, env, and timeout handling)
- Removed `paperclipApiUrl` from `SshRemoteExecutionSpec`; the bridge
URL now flows
  through the shared runner
- Reworked `execution-target.ts` to use the SSH runner alongside sandbox
runners
  via a unified `CommandManagedRuntimeRunner` interface
- Simplified `remote-managed-runtime.ts` and
`sandbox-managed-runtime.ts` to consume
  the shared runner abstraction
- Deleted per-adapter SSH callback wiring from claude-local,
codex-local,
  cursor-local, gemini-local, opencode-local, pi-local execute.ts files
- Removed `environment-runtime-driver-contract.test.ts` (the contract is
now
  enforced by `environment-execution-target.test.ts`)
- Added/updated `execute.remote.test.ts` cases for each adapter to cover
the SSH
  runner path

## Verification

- `pnpm --filter @paperclipai/adapter-utils test`
- `pnpm test -- execute.remote` (covers all six local adapters' SSH
paths)
- Manual QA: ran a claude-local agent against an SSH-backed environment,
confirmed
the agent successfully called back to `/api/agent-callback/*` endpoints
during
  the run

## Risks

- Refactor touches all six local adapters. If any adapter had subtle
SSH-specific
behaviour that wasn't captured in tests, it could regress. Mitigation:
each
  adapter's `execute.remote.test.ts` was extended.
- `paperclipApiUrl` removal from `SshRemoteExecutionSpec` is a breaking
type change
for any internal consumer. Verified no external plugins consume this
type.
- The new `CommandManagedRuntimeRunner` shape is a public surface in
`@paperclipai/adapter-utils`; downstream plugins implementing custom
runners may
  need updates, but no such plugins exist in this repo.

## Model Used

- OpenAI GPT-5.4 (reasoning effort: high) via Codex CLI
- Provider: OpenAI
- Used to author the code changes in this PR

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots — N/A
- [ ] I have updated relevant documentation to reflect my changes — N/A
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

packages/adapter-utils/src/execution-target-sandbox.test.ts

@@ -7,6 +7,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import {
   adapterExecutionTargetSessionIdentity,
   adapterExecutionTargetToRemoteSpec,
+  adapterExecutionTargetUsesPaperclipBridge,
   runAdapterExecutionTargetProcess,
   runAdapterExecutionTargetShellCommand,
   startAdapterExecutionTargetPaperclipBridge,
@@ -104,7 +105,6 @@ describe("sandbox adapter execution targets", () => {
       environmentId: "env-1",
       leaseId: "lease-1",
       remoteCwd: "/workspace",
-      paperclipTransport: "bridge",
     });
   });
 
@@ -141,6 +141,33 @@ describe("sandbox adapter execution targets", () => {
     }));
   });
 
+  it("treats SSH targets as bridge-only", () => {
+    const target = {
+      kind: "remote" as const,
+      transport: "ssh" as const,
+      remoteCwd: "/workspace",
+      spec: {
+        host: "ssh.example.test",
+        port: 22,
+        username: "paperclip",
+        remoteWorkspacePath: "/workspace",
+        remoteCwd: "/workspace",
+        privateKey: null,
+        knownHosts: null,
+        strictHostKeyChecking: true,
+      },
+    };
+
+    expect(adapterExecutionTargetUsesPaperclipBridge(target)).toBe(true);
+    expect(adapterExecutionTargetSessionIdentity(target)).toEqual({
+      transport: "ssh",
+      host: "ssh.example.test",
+      port: 22,
+      username: "paperclip",
+      remoteCwd: "/workspace",
+    });
+  });
+
   it("uses the provider-declared shell for sandbox helper commands", async () => {
     const runner = {
       execute: vi.fn(async () => ({
@@ -210,7 +237,6 @@ describe("sandbox adapter execution targets", () => {
       environmentId: "env-1",
       leaseId: "lease-1",
       remoteCwd,
-      paperclipTransport: "bridge",
       runner: createLocalSandboxRunner(),
       timeoutMs: 30_000,
     };
@@ -288,7 +314,6 @@ describe("sandbox adapter execution targets", () => {
       environmentId: "env-1",
       leaseId: "lease-1",
       remoteCwd,
-      paperclipTransport: "bridge",
       runner: createLocalSandboxRunner(),
       timeoutMs: 30_000,
     };