agent (unreleased): fixes after an independent review — one lock for the writers of agent.json, the trust run serialised and bounded, the CA copy keeps its previous root, the profile stanza from the wrapper's answer, a stale give-up ends, both boot tokens from one read

Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

internal/config/filelock.go

@@ -0,0 +1,12 @@
+package config
+
+import "sync"
+
+// FileMu is held by EVERY read-modify-write of agent.json inside this process: the trust move (pvetrust), the PBS
+// seed (pbsdr) and the backup-target move (localapi). Each of them reads the whole file, changes one section and
+// writes the whole file back in place — without one lock two of them could interleave, and the second writer would
+// put back the document it read BEFORE the first one's change (a silently reverted `escrow.pbs_storage_id`,
+// `backup.local_backup_target` or trust section). Found by review on 2026-11-14, the night the third writer was
+// added. Hold it for the whole read … write, never across a call to Proxmox or the root wrapper.
+// Pinned by TestAgentJSONWritersTakeTheSharedLock (cmd/felhom-agent).
+var FileMu sync.Mutex