fix: remove explicit repo mount from pi-agent manifest and derive workspace name from remote URL

The pi-agent manifest still declared an explicit repo mount with
{{WORKSPACE_NAME}}, making the mount target dependent on tool config. The
instance service now synthesizes the repo mount, so the manifest no longer
needs the explicit mount.

- Add Alembic migration 2026_06_15_090500 to remove the source_type: repo
  mount from the built-in pi-agent manifest
- Add _get_repository_mount_name() helper to derive the workspace directory
  name from the repository remote URL (matching git clone behavior) and
  fall back to the user-provided repository name
- Use the helper for WORKSPACE_NAME/REPO_NAME in manifest, legacy dockerfile,
  and legacy compose template paths
- Update unit tests for the new migration and helper

Quality gates:
- pytest tests/unit: 218 passed
- ruff: clean on changed files
- mypy: clean on changed files
- alembic heads: single head

apps/api/tests/unit/test_instance_service.py

@@ -4,7 +4,11 @@ from unittest.mock import MagicMock, AsyncMock
 
 import pytest
 
-from src.services.tool.instance_service import modify_compose_file, prepare_manifest_instance
+from src.services.tool.instance_service import (
+    _get_repository_mount_name,
+    modify_compose_file,
+    prepare_manifest_instance,
+)
 
 
 @pytest.mark.unit
@@ -14,7 +18,7 @@ class TestModifyComposeFile:
     def test_extra_volumes_expand_home_dir(self, tmp_path):
         compose_path = tmp_path / "docker-compose.yml"
         compose_path.write_text(
-            'services:\n  app:\n    image: test:latest\n    volumes: []\n'
+            "services:\n  app:\n    image: test:latest\n    volumes: []\n"
         )
 
         modify_compose_file(
@@ -32,9 +36,7 @@ class TestModifyComposeFile:
 
     def test_working_directory_expands_home_dir(self, tmp_path):
         compose_path = tmp_path / "docker-compose.yml"
-        compose_path.write_text(
-            'services:\n  app:\n    image: test:latest\n'
-        )
+        compose_path.write_text("services:\n  app:\n    image: test:latest\n")
 
         modify_compose_file(
             str(compose_path),
@@ -46,11 +48,41 @@ class TestModifyComposeFile:
         assert "working_dir: /home/user/workspace" in content
 
 
+@pytest.mark.unit
+class TestGetRepositoryMountName:
+    """Tests for _get_repository_mount_name."""
+
+    def test_prefers_remote_url_name_over_user_provided_name(self):
+        repo = MagicMock()
+        repo.name = "src"
+        repo.remote_url = "git@git.example.com:acme/headquarter.git"
+        assert _get_repository_mount_name(repo) == "headquarter"
+
+    def test_parses_browser_url_to_repo_name(self):
+        repo = MagicMock()
+        repo.name = "src"
+        repo.remote_url = "https://github.com/acme/headquarter/tree/main"
+        assert _get_repository_mount_name(repo) == "headquarter"
+
+    def test_falls_back_to_repo_name_when_remote_url_missing(self):
+        repo = MagicMock()
+        repo.name = "my-cool-repo"
+        repo.remote_url = None
+        assert _get_repository_mount_name(repo) == "my-cool-repo"
+
+    def test_falls_back_to_repo_name_for_unparseable_url(self):
+        repo = MagicMock()
+        repo.name = "my-cool-repo"
+        repo.remote_url = ""
+        assert _get_repository_mount_name(repo) == "my-cool-repo"
+
+
 @pytest.mark.unit
 async def test_prepare_manifest_instance_uses_repo_name_not_workspace_dir():
     """WORKSPACE_NAME must be the repository name, not the workspace path basename."""
     repo = MagicMock()
-    repo.name = "my-cool-repo"
+    repo.name = "src"
+    repo.remote_url = "git@git.example.com:acme/headquarter.git"
     repo.path = "/data/repos/main"
 
     tool_type = MagicMock()
@@ -63,13 +95,12 @@ async def test_prepare_manifest_instance_uses_repo_name_not_workspace_dir():
         "base_image": "ubuntu:24.04",
         "interface_type": "terminal",
         "user": {"name": "user", "uid": 1001, "gid": 1001},
-        "mounts": [{"name": "workspace", "target": "~/{{WORKSPACE_NAME}}", "source_type": "repo"}],
     }
     manifest_def.base_definition_id = None
 
     instance = MagicMock()
     instance.id = "instance-uuid"
-    instance.name = "pi-agent-my-cool-repo-abc123"
+    instance.name = "pi-agent-headquarter-abc123"
     instance.repository_id = "repo-uuid"
     instance.tool_type_id = "tooltype-uuid"
     instance.port = 0
@@ -95,16 +126,23 @@ async def test_prepare_manifest_instance_uses_repo_name_not_workspace_dir():
     from src.services.tool import instance_service
 
     original_run = subprocess.run
+
     def fake_run(cmd, **kwargs):
         class Result:
             returncode = 0
             stdout = "image-id"
             stderr = ""
+
         return Result()
 
     instance_service.subprocess.run = fake_run
     try:
-        image_tag, compose_content, manifest, home_dir = await prepare_manifest_instance(
+        (
+            image_tag,
+            compose_content,
+            manifest,
+            home_dir,
+        ) = await prepare_manifest_instance(
             session=session,
             instance=instance,
             instance_dir="/tmp/instance",
@@ -116,5 +154,5 @@ async def test_prepare_manifest_instance_uses_repo_name_not_workspace_dir():
     finally:
         instance_service.subprocess.run = original_run
 
-    assert "WORKSPACE_NAME: my-cool-repo" in compose_content
-    assert "/data/repos/main:/home/user/my-cool-repo" in compose_content
+    assert "WORKSPACE_NAME: headquarter" in compose_content
+    assert "/data/repos/main:/home/user/headquarter" in compose_content