Finish the file API traversal fix by rooting both GET and SET operations at the
actual file-type directory instead of the process working directory. This blocks
`..` escapes from `config/` and `config/middlewares/` while preserving valid
in-root reads and writes.
Also harden the optional unauthenticated local API listener so it only starts on
loopback addresses (`localhost`, `127.0.0.1`, `::1`). This preserves same-host
automation while preventing accidental exposure on wildcard, LAN, bridge, or
public interfaces.
Add regression tests for blocked traversal on GET and SET, valid in-root writes,
and loopback-only local API address validation. Fix an unrelated config test
cleanup panic so the touched package verification can run cleanly.
Constraint: `GODOXY_LOCAL_API_ADDR` is documented for local automation and must remain usable without adding a new auth flow
Constraint: File API behavior must keep valid config/provider/middleware edits working while blocking path escapes
Rejected: Mirror the previous GET `OpenInRoot(".", ...)` approach in SET | still allows escapes from `config/` to sibling paths under the working directory
Rejected: Keep unauthenticated non-loopback local API binds and document the risk | preserves a high-severity pre-auth network exposure
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Treat `LOCAL_API_ADDR` as same-host only; if non-loopback unauthenticated access is ever needed, gate it behind a separately named explicit insecure opt-in
Tested: `go test -count=1 -ldflags='-checklinkname=0' ./internal/api/v1/file -run 'Test(Get|Set)_PathTraversalBlocked' -v`
Tested: `go test -count=1 -ldflags='-checklinkname=0' ./internal/config -run '^TestValidateLocalAPIAddr$|^TestRouteValidateInboundMTLSProfile$' -v`
Tested: `go test -count=1 -ldflags='-checklinkname=0' ./internal/api/... ./internal/config/...`
Not-tested: End-to-end runtime verification of fsnotify reload behavior after a valid in-root provider edit
Use os.OpenRoot to restrict file access to the application root,
preventing directory traversal attacks through the file download endpoint.
Also add test to verify path traversal attempts are blocked.
