feat: add recoverable sync and read-only checks

README.md

@@ -276,6 +276,13 @@ skillsync target add codex ~/.codex/skills --no-auto-adopt
 
 If a different skill with the same name is already in the vault, SkillSync leaves both copies untouched and reports the conflict.
 
+Inspect local targets without adopting, applying, committing, or pushing anything:
+
+```bash
+skillsync scan
+skillsync scan --json
+```
+
 ## Manage another device
 
 List registered devices and their sync state:
@@ -341,6 +348,32 @@ Run a sync immediately:
 skillsync sync
 ```
 
+Preview local skill projection changes without pulling or writing:
+
+```bash
+skillsync sync --dry-run
+```
+
+SkillSync checks every destination before applying the plan. It backs up changed skill projections in local Git metadata and restores them if the apply or a later local reconciliation step fails. Copy-mode projections also record their deployed content hash. If a managed copy was edited locally, sync stops instead of overwriting it. After reviewing those edits, discard them explicitly with:
+
+```bash
+skillsync sync --discard-local-changes
+```
+
+Restore the most recent successful local projection apply in an emergency:
+
+```bash
+skillsync rollback
+```
+
+The next sync applies the current vault assignments again.
+
+Validate vault structure, registry hashes, JSON files, symlinks, and common credential formats without changing the vault:
+
+```bash
+skillsync check
+```
+
 Inspect the current configuration:
 
 ```bash
@@ -406,8 +439,10 @@ skillsync target auto-adopt <name> <on|off>
 skillsync auto-adopt [show|on|off]
 skillsync policy show
 skillsync policy set delete-unassigned-skills <on|off>
-skillsync scan
-skillsync sync
+skillsync scan [--json]
+skillsync sync [--dry-run] [--no-pull] [--discard-local-changes]
+skillsync rollback
+skillsync check
 skillsync service install
 skillsync doctor
 skillsync daemon
@@ -416,6 +451,9 @@ skillsync daemon
 ## Safety
 
 - SkillSync will not silently overwrite an unmanaged local folder.
+- SkillSync refuses to overwrite or remove a locally edited managed copy unless you explicitly discard the edits.
+- Skill projection applies restore their previous state after a failure.
+- Vault checks reject symlinks, malformed JSON, stale registry entries, reserved ownership markers, and common credential formats.
 - Symlinked content outside a configured target is not auto-adopted.
 - Different same-name skills require explicit conflict resolution.
 - Plugin sync is additive and never copies connector credentials.

SECURITY.md

@@ -23,3 +23,5 @@ SkillSync uses a user-owned private GitHub repository as its control plane. Ever
 Device-local skill targets and global instruction paths are approved on that device and stored outside the synced vault. Pulled vault state cannot authorize new local filesystem locations.
 
 Skill folders can contain executable instructions or supporting scripts. Users should review third-party skills before adding them to a vault.
+
+SkillSync checks vault files for symlinks, malformed JSON, stale registry entries, reserved ownership markers, and common credential formats before syncing or pushing. This check reduces accidental exposure but cannot recognize every secret. Keep credentials, OAuth state, and session data out of skill folders and instruction profiles.