Canvas Extensions: Phase 1 test matrix

• Install sources: git ref, SHA, repo subpath, local path.
• Disabled-by-default, duplicate installs, invalid/malformed manifests, smuggled enabled: true payloads.
• Traversal/symlink-escape adversarial cases (security-owned review, not routine QA).
• Untracked directory placed directly in the install root is discovered but never auto-enabled.
• Refresh check never mutates or deactivates the active bundle; refresh apply requires its own fresh reconfirmation rather than reusing the install-time or a prior refresh's confirmation.
• Persistence, rollback, uninstall, 404s, auth, multi-backend switching.

Reference test files to extend/mirror: tests/sdk/extensions/installation/test_installation_manager.py and test_installation_metadata.py already cover the generic framework's happy paths. The disabled-by-default and self-heal-auto-enable cases above are gaps in that existing suite too, not just a canvas-extensions gap — e.g. test_installation_manager.py:172-182 has to explicitly call .disable() before testing force-reinstall preservation, because there's no existing test asserting a bare fresh install defaults to disabled.

Blocked by: OpenHands/software-agent-sdk#4352

First review the blocker, OpenHands/software-agent-sdk#4352. Then extend or mirror tests/sdk/extensions/installation/test_installation_manager.py and test_installation_metadata.py, including the referenced lines 172-182. Run the installation test suite and consider the matrix complete when the listed source, disabled-by-default, security, refresh, persistence, rollback, uninstall, error, authentication, and backend-switching cases are covered.