feat(author): add dirty-preserving same-claimant author-session rebind (Closes #864)

Introduce an explicit, fail-closed recovery operation that rebinds a live
author session to an already-registered dirty issue worktree when the durable
lock still belongs to the same identity/profile and the recorded owner PID is
provably dead. Ordinary locking remains clean-worktree-only; this path updates
only stale lock/session provenance, preserves every dirty byte under fingerprint
pins, and grants create-PR-sanctioned provenance without remote sync or recovery
worktrees.

Also stop treating dead-owner session pointers as live mutation workspace
bindings so a stale dead-owner pointer cannot poison unrelated author work.

issue_lock_provenance.py

@@ -16,11 +16,16 @@ ISSUE_LOCK_FILE = os.environ.get("GITEA_ISSUE_LOCK_FILE", "/tmp/gitea_issue_lock
 SOURCE_LOCK_ISSUE = "gitea_lock_issue"
 SOURCE_LOCK_ADOPTION = "gitea_lock_issue_adoption"
 SOURCE_OPERATOR_OVERRIDE = "operator_override"
+# #864: dirty-preserving same-claimant author-session rebind (dead owner PID).
+SOURCE_DIRTY_SAME_CLAIMANT_REBIND = (
+    "gitea_rebind_dirty_same_claimant_author_session"
+)
 
 SANCTIONED_LOCK_SOURCES = frozenset({
     SOURCE_LOCK_ISSUE,
     SOURCE_LOCK_ADOPTION,
     SOURCE_OPERATOR_OVERRIDE,
+    SOURCE_DIRTY_SAME_CLAIMANT_REBIND,
 })
 
 _OPERATOR_OVERRIDE_ENV = "GITEA_ISSUE_LOCK_OPERATOR_OVERRIDE"