Add scoped secret store to isolate system-managed tokens from user secrets

Background

ToolHive's secret management uses a flat keyspace — all secrets share the same namespace in the backing store. Users can list, read, and delete any secret via `thv secret list/get/delete`.

Several system-managed tokens are currently stored in this flat namespace and are visible to users:

Key pattern	Source
`REGISTRY_OAUTH_`	`thv registry login` refresh tokens
`OAUTH_CLIENT_SECRET_`	Remote workload OAuth client secrets
`BEARER_TOKEN_`	Remote workload bearer tokens
`OAUTH_REFRESH_TOKEN_`	Remote workload OAuth refresh tokens

These are internal system credentials. Exposing them via `thv secret list` is confusing and risky — users can accidentally overwrite or delete tokens that workloads depend on.

Proposed Solution

Introduce a `ScopedProvider` and `UserProvider` wrapper layer in `pkg/secrets/`. System callers get a scoped provider that prefixes every key with `_thv_`. User-facing callers get a `UserProvider` wrapper that hides and blocks access to any key starting with `_thv`.

Full design details: THV-0056 RFC

Key prefix format

__thv_registry_REGISTRY_OAUTH_a1b2c3d4      ← registry OAuth refresh tokens
__thv_workloads_BEARER_TOKEN_github-app     ← remote workload auth tokens
__thv_workloads_OAUTH_CLIENT_SECRET_foo     ← remote workload OAuth client secrets
__thv_auth_access_token                     ← reserved for future enterprise login
<user-key>                                  ← user-managed secrets (unchanged)

Scope constants

const (
    SystemKeyPrefix = "__thv_"
    ScopeRegistry   = "registry"   // pkg/registry/auth/
    ScopeWorkloads  = "workloads"  // pkg/auth/secrets/
    ScopeAuth       = "auth"       // future: enterprise login tokens
)

New types in `pkg/secrets/scoped.go`

`ScopedProvider` — for system callers:

• `GetSecret/SetSecret/DeleteSecret` transparently prefix the key with `_thv_`
• `ListSecrets` returns only entries in that scope, with prefix stripped
• `Cleanup` performs a prefix-filtered delete using `BulkDeleteKeys`

`UserProvider` — for user-facing callers:

• `ListSecrets` filters out any key starting with `_thv`
• `Get/Set/Delete` of a reserved-prefix key returns `ErrReservedKeyName`
• `Cleanup` uses `BulkDeleteKeys` to remove only non-system keys

New methods on `EncryptedManager`

// BulkRenameKeys renames multiple keys atomically under a single file lock
// with a single updateFile() call. Store-before-Delete ordering ensures
// concurrent readers always see the value under at least one key.
func (e *EncryptedManager) BulkRenameKeys(renames map[string]string) error

// BulkDeleteKeys deletes multiple keys atomically under a single file lock
// with a single updateFile() call.
func (e *EncryptedManager) BulkDeleteKeys(keys []string) error

Factory helpers in `pkg/secrets/factory.go`

// CreateScopedSecretProvider returns a provider for system-managed tokens.
// Does NOT apply FallbackProvider — system tokens must not come from env vars.
// Returns an error if managerType is EnvironmentType.
func CreateScopedSecretProvider(managerType ProviderType, scope string) (Provider, error)

// CreateUserSecretProvider returns a provider for user-managed secrets.
// Wraps with UserProvider to hide and block system-reserved keys.
func CreateUserSecretProvider(managerType ProviderType) (Provider, error)

Implementation Plan

Phase 1 — Core types (pkg/secrets/scoped.go + scoped_test.go) — additive, no wiring yet ✅ Done

Phase 2 — Factory helpers and bulk EncryptedManager methods

• Add `BulkRenameKeys` and `BulkDeleteKeys` to `EncryptedManager` in `pkg/secrets/encrypted.go`
• Add `CreateScopedSecretProvider` and `CreateUserSecretProvider` to `pkg/secrets/factory.go`
• Update `pkg/secrets/factory_test.go` and `pkg/secrets/encrypted_test.go`

Phase 3 — System callers (ships simultaneously with Phases 4 and 5)

• `pkg/auth/secrets/secrets.go` → `GetSecretsManager()` uses `ScopeWorkloads`
• `pkg/registry/factory.go` → `resolveTokenSource()` uses `ScopeRegistry`
• `cmd/thv/app/registry_login.go:77` → uses `ScopeRegistry`

Phase 4 — User callers (ships simultaneously with Phases 3 and 5)

• `cmd/thv/app/secret.go`, `pkg/api/v1/secrets.go`
• `cmd/thv/app/config_buildauthfile.go` (4 calls — `BUILD_AUTH_FILE_*` are user-managed)
• `cmd/thv/app/config_buildenv.go`, `cmd/thv/app/header_flags.go`
• `pkg/runner/protocol.go`, `pkg/runner/runner.go`, `pkg/workloads/manager.go`
• `pkg/mcp/server/list_secrets.go`, `set_secret.go`

Phase 5 — Key migration (ships simultaneously with Phases 3 and 4)

• Add `pkg/secrets/migration.go` with `MigrateSystemKeys`
• Uses `BulkRenameKeys` for a single atomic file write — not optional
• Guard with config flag to run exactly once

Phase 6 — Admin escape hatch

• Add `--system` flag to `thv secret list` and `thv secret delete`
• Document as advanced/emergency commands for managing stale or leaked system tokens

Risks

Risk	Mitigation
Existing users lose cached tokens	Phase 5 migration ships simultaneously with Phases 3+4
FallbackProvider + ScopedProvider ordering	CreateScopedSecretProvider skips fallback entirely
UserProvider.Cleanup() wipes system tokens	BulkDeleteKeys scoped to non-system keys only
EnvironmentType provider used as system store	CreateScopedSecretProvider returns error for EnvironmentType
1Password / path separator conflict	__thv_ prefix uses no slashes — conflict eliminated by construction

Acceptance Criteria

• ScopedProvider and UserProvider implemented in pkg/secrets/scoped.go with unit tests
• BulkRenameKeys and BulkDeleteKeys added to EncryptedManager
• CreateScopedSecretProvider and CreateUserSecretProvider factory helpers added
• thv secret list no longer shows REGISTRY_OAUTH_*, OAUTH_CLIENT_SECRET_*, BEARER_TOKEN_*, or OAUTH_REFRESH_TOKEN_* keys
• thv secret get/set/delete with an __thv_ prefix returns a clear error message
• All system callers updated to use CreateScopedSecretProvider (including registry_login.go)
• All user callers updated to use CreateUserSecretProvider
• Key migration runs on first startup and atomically moves legacy system keys to scoped equivalents
• thv secret list --system and thv secret delete --system available for emergency use
• All existing secret management behavior is unchanged for user-managed secrets
• ScopeAuth constant reserved for future enterprise login tokens

Start with the THV-0056 RFC, then inspect pkg/secrets/scoped.go and scoped_test.go to understand the completed core types. Next read pkg/secrets/encrypted.go, pkg/secrets/factory.go, and their tests before tracing the listed system and user callers. Run the relevant secrets tests; done means atomic migration, scoped system access, protected user access, updated callers, and the documented CLI escape hatch.