agent0ai/space-agent/backend-reference

Use this skill when frontend work depends on understanding backend behavior. This skill is read-only context, not authorization to change backend files.

Hard Boundary

• Do not edit server/, commands/, or packaging/ from this skill set.
• If the task truly requires backend changes, stop and ask instead of treating this skill as permission.
• Backend changes are non-standard in this project. Only ask for them when frontend-only work cannot safely enforce security, integrity, cross-user isolation, or runtime stability.
• When you ask, explain why the frontend solution would be insufficient and describe the narrow backend change required.

Page And Request Flow

Current request order is:

1. API preflight handling
2. /api/proxy
3. /api/<endpoint>
4. /mod/...
5. /~/... and /L0/..., /L1/..., /L2/...
6. page shells and page actions

The browser app mounts through page shells in server/pages/. /login is public. / and /admin require authentication.

API Families

Important frontend-facing endpoint families are:

• app files: file_list, file_paths, file_read, file_write, file_delete, file_copy, file_move, file_info, folder_download
• local history: git_history_list, git_history_diff, git_history_preview, git_history_rollback, git_history_revert
• modules: module_list, module_info, module_install, module_remove
• runtime and identity: extensions_load, password_generate, password_change, user_crypto_session_key, user_self_info

These endpoints are thin wrappers over shared helpers in server/lib/customware/ and server/lib/auth/.

file_write still defaults to whole-file replacement, but it also supports operation: "append", "prepend", and "insert". Insert writes accept exactly one anchor through line, before, or after, use the first literal before or after match, treat line as a 1-based insertion point, and require utf8.

file_list and file_paths support access: "write" or writableOnly: true for writable-only discovery. They also support gitRepositories: true; with a pattern such as **/.git/, file_paths returns local-history owner roots like L1/team/ and L2/alice/ without exposing reserved .git metadata paths.

folder_download supports HEAD for permission-only validation and GET or POST for the streamed ZIP attachment. It creates the archive in server/tmp/ only for the actual download response, after the shared file-access layer approves the requested folder path.

git_history_list, git_history_diff, git_history_preview, git_history_rollback, and git_history_revert are enabled by CUSTOMWARE_GIT_HISTORY. The backend maps the requested path to a writable L1/<group>/ or L2/<user>/ owner repo, enforces permissions, paginates list metadata with optional file filters, reads per-file diffs separately, previews travel or revert affected files with optional operation-specific file patches, suppresses history scheduling during rollback, preserves ignored L2 auth files, preserves forward-travel refs during rollback when possible, and creates inverse commits for revert.

user_self_info is the frontend-facing identity snapshot. Frontend callers derive writable app roots from username, managedGroups, and _admin membership in groups without authorizing backend edits.

password_change is the authenticated self-service password-rotation endpoint for the current user. Frontend code should call it instead of writing ~/meta/password.json directly, because the backend validates the current password, seals the replacement verifier, clears sessions, and clears the current auth cookie.

user_crypto_session_key is the authenticated localStorage-restore endpoint. It returns the current session-derived wrapping key by hashing the live backend sessionId with the server-held session secret, so the browser can decrypt or encrypt the one persisted userCrypto localStorage blob without the server persisting that wrapping key or the user master key.

Module And Extension Resolution

• /mod/... resolution goes through the layered customware model.
• maxLayer constrains module and extension resolution and defaults to 2.
• /admin effectively clamps module and extension resolution to L0.
• Frontend HTML extensions resolve through ext/html/....
• Frontend JS hooks resolve through ext/js/....
• Frontend modules may also enumerate other extension-owned assets such as ext/panels/*.yaml through file_paths plus file_read when they only need readable logical file discovery and contents. extensions_load remains the backend contract for HTML and JS extension resolution, keeping maxLayer at the top level, ordered patterns groups in the request, and ordered grouped results with matching patterns plus resolved extensions.

Auth And User Storage

• The server issues the space_session cookie and validates it by hashing it with a backend-held secret.
• When the current login may auto-restore userCrypto on the same browser profile, the browser stores one encrypted userCrypto blob in localStorage, and authenticated browser code fetches the current session-derived wrapping key from /api/user_crypto_session_key.
• User metadata lives at L2/<username>/user.yaml.
• L2/<username>/meta/password.json stores a server-sealed SCRAM verifier envelope, not a self-sufficient plaintext verifier.
• L2/<username>/meta/logins.json stores backend-keyed session verifiers plus signed session metadata.
• Authenticated self-service password changes still stay backend-owned through /api/password_change; browser code may edit L2/<username>/user.yaml directly, but not the password verifier file.
• User-owned modules live under L2/<username>/mod/.
• Backend auth keys come from shared environment injection through SPACE_AUTH_PASSWORD_SEAL_KEY and SPACE_AUTH_SESSION_HMAC_KEY for multi-instance deployments, or from the local fallback server/data/auth_keys.json during single-instance development.

Why Frontend Developers Need This

• to understand why a frontend file API call succeeds or fails
• to understand where module and extension inheritance comes from
• to understand why admin UI is firmware-clamped while normal app routing is layered
• to understand the user and group storage model without editing backend logic
• to identify the small set of cases where backend ownership is mandatory instead of merely convenient

Mandatory Doc Follow-Up

• If backend contracts that the frontend depends on change, update the mirrored backend docs and the development skill subtree in the same session, even though this skill remains read-only guidance.