fix(tier2): override MCP server path + reset mcp_paths.toml in clone

Follow-up to 9cd85364. The previous fix patched the OpenCode session-
level permission.read/write allowlist to include the sandbox clone
path, but Tier 2 was still hitting 'ACCESS DENIED' on clone paths.

Root cause: the MCP server has its OWN allowlist that's separate from
OpenCode's session-level permission. The MCP server's allowlist =
project_root (parent dir of the script) + extra_dirs from
mcp_paths.toml in the project root. The clone inherited the main
repo's mcp.manual-slop.command via 'git clone', which launched
C:\\projects\\manual_slop\\scripts\\mcp_server.py with
PYTHONPATH=C:\\projects\\manual_slop\\src. So the MCP server was
using the main repo's project_root + the main repo's mcp_paths.toml
(extra_dirs=['C:/projects/gencpp']) -- exactly the
'Allowed base directories are: gencpp, manual_slop' the user saw.

Fix: setup_tier2_clone.ps1 now overrides the clone's mcp.manual-slop
config to point at the CLONE's scripts/mcp_server.py and src/, and
replaces the clone's mcp_paths.toml with an empty extra_dirs list.
The MCP server's allowlist becomes [C:\\projects\\manual_slop_tier2]
only -- the sandbox boundary.

Added test_setup_script_overrides_mcp_server (text-based regression)
to assert the script contains the required overrides. Opt-in via
TIER2_SANDBOX_TESTS=1.

Verified: re-ran setup against the live clone. opencode.json now has
mcp.manual-slop.command pointing at C:\\projects\\manual_slop_tier2\\
scripts\\mcp_server.py with PYTHONPATH=C:\\projects\\manual_slop_tier2\\
src. mcp_paths.toml has 'extra_dirs = []'.

scripts/tier2/setup_tier2_clone.ps1

@@ -83,8 +83,36 @@ if ($PSCmdlet.ShouldProcess("Bootstrap Tier 2 clone at $Tier2ClonePath")) {
             $existing | ConvertTo-Json -Depth 10 | Set-Content $cloneConfig
         } else {
             Copy-Item -Force "$MainRepoPath\conductor\tier2\opencode.json.fragment" $cloneConfig
+            $existing = $fragment
         }
 
+        # Override the MCP server's command + PYTHONPATH to point at the
+        # Tier 2 clone's files. The inherited config points to the main
+        # repo's scripts/mcp_server.py, which loads the main repo's
+        # project_root (C:\projects\manual_slop) and reads the main repo's
+        # mcp_paths.toml (which allowlists C:\projects\gencpp). When Tier 2
+        # calls manual-slop_read_file on a clone path, the MCP server
+        # rejects it with "Allowed base directories are: manual_slop, gencpp".
+        # The fix: launch the MCP server from the clone's path with the
+        # clone's PYTHONPATH, and replace the clone's mcp_paths.toml with
+        # an empty one so the clone's MCP server has no extra_dirs.
+        if ($existing.mcp -and $existing.mcp.'manual-slop') {
+            $existing.mcp.'manual-slop'.command = @(
+                "$env:USERPROFILE\scoop\apps\uv\current\uv.exe",
+                "run",
+                "python",
+                "$Tier2ClonePath\scripts\mcp_server.py"
+            )
+            $existing.mcp.'manual-slop'.environment.PYTHONPATH = "$Tier2ClonePath\src"
+            $existing | ConvertTo-Json -Depth 10 | Set-Content $cloneConfig
+        }
+        $cloneMcpPaths = "$Tier2ClonePath\mcp_paths.toml"
+        @"
+[allowed_paths]
+extra_dirs = []
+"@ | Set-Content -Path $cloneMcpPaths -NoNewline
+        Write-Host "[tier2-bootstrap] MCP server pointed at clone; mcp_paths.toml reset to empty extra_dirs"
+
         # 4. Install git hooks
         Write-Host "[tier2-bootstrap] installing git hooks"
         Copy-Item -Force "$MainRepoPath\conductor\tier2\githooks\pre-push" "$Tier2ClonePath\.git\hooks\pre-push"