diff --git a/functions/agents-vault.fish b/functions/agents-vault.fish
index 1971682..351e49a 100644
--- a/functions/agents-vault.fish
+++ b/functions/agents-vault.fish
@@ -35,6 +35,14 @@
 #   of megabytes per project, growing per session). Paths are allowlisted,
 #   never denylisted, so nothing new upstream adds can leak in.
 #
+#   Because the slug is derived from the remote, gaining, losing, or
+#   rewriting a project's origin changes it. Each run detects this by
+#   reading the previous slug straight off the live memory symlink's
+#   target (no guessing) and migrates that entry to the new slug before
+#   relinking, so memory accumulated under the old key is never orphaned.
+#   If both the old and new entries already hold content the migration is
+#   ambiguous and is refused; resolve it with --adopt=SLUG.
+#
 # ARGUMENTS
 #   --link         Scaffold the vault and link this project's memory; skip
 #                  the final commit
@@ -202,6 +210,56 @@ function agents-vault --description 'track curated agent memory in a host-scoped
         set -l entry "$vault/projects/$slug"
         set -l vmem "$entry/claude/memory"
 
+        set -l claude_root $__fish_agent_vault_claude_root
+        test -n "$claude_root"; or set claude_root "$HOME/.claude/projects"
+        set -l mangled (string replace -a '/' '-' -- "$root" | string replace -a '.' '-')
+        set -l live "$claude_root/$mangled/memory"
+
+        # ── Slug migration (spec 4.5) ─────────────────────────────────────
+        # The previous slug never has to be guessed: the live symlink still
+        # points at the old entry. This covers a remote being added, a
+        # remote URL being rewritten, and a remote being removed.
+        set -l prev_slug ""
+        if test -L "$live"
+            set -l tgt (path resolve "$live")
+            set -l pdir (path resolve "$vault/projects")
+            if string match -q "$pdir/*" -- "$tgt"
+                set -l rest (string replace "$pdir/" "" -- "$tgt")
+                set prev_slug (string split -f1 '/' -- $rest)
+            end
+        end
+        if test -z "$prev_slug"
+            # No link yet (fresh machine): try the path-derived candidate.
+            set -l cand_rp (path resolve "$root")
+            set -l cand_base (string lower -- (path basename "$cand_rp"))
+            set -l cand_digest (printf '%s' "$cand_rp" | sha256sum | string split -f1 ' ')
+            set -l cand "local-$cand_base-"(string sub -l 8 -- "$cand_digest")
+            if test "$cand" != "$slug"; and test -d "$vault/projects/$cand"
+                set prev_slug $cand
+            end
+        end
+
+        if test -n "$prev_slug"; and test "$prev_slug" != "$slug"
+            set -l prev_mem "$vault/projects/$prev_slug/claude/memory"
+            set -l cur_content
+            test -d "$vmem"; and set cur_content (command ls -A "$vmem" 2>/dev/null)
+            if test (count $cur_content) -gt 0
+                echo "$c_err""agents-vault: cannot migrate $prev_slug → $slug; both entries hold content.$c_reset" >&2
+                echo "$c_err""  Resolve with: agents-vault --adopt=SLUG$c_reset" >&2
+                return 1
+            end
+            test -d "$vmem"; and rm -rf "$vault/projects/$slug"
+            mkdir -p (path dirname "$vault/projects/$slug")
+            if not git -C "$vault" mv "projects/$prev_slug" "projects/$slug" 2>/dev/null
+                command mv "$vault/projects/$prev_slug" "$vault/projects/$slug"; or return 1
+            end
+            printf 'renamed: %s → %s (%s)\n' "$prev_slug" "$slug" (date -I) \
+                >>"$vault/projects/$slug/origin"
+            rm -f "$live"
+            set changed 1
+            test $verbose -eq 1; and echo "$c_ok→ Migrated vault entry $prev_slug → $slug$c_reset"
+        end
+
         if not test -d "$vmem"
             if not mkdir -p "$vmem"
                 echo "$c_err""agents-vault: could not create $vmem$c_reset" >&2
@@ -210,11 +268,6 @@ function agents-vault --description 'track curated agent memory in a host-scoped
             set changed 1
         end
 
-        set -l claude_root $__fish_agent_vault_claude_root
-        test -n "$claude_root"; or set claude_root "$HOME/.claude/projects"
-        set -l mangled (string replace -a '/' '-' -- "$root" | string replace -a '.' '-')
-        set -l live "$claude_root/$mangled/memory"
-
         # Unconditional: this is the emergent-restore path. On a freshly
         # cloned vault, $vmem already exists (populated from the clone) and
         # $live does not exist yet -- skipping the link here would silently
diff --git a/tests/test-agents-vault.fish b/tests/test-agents-vault.fish
index 289c587..a443329 100644
--- a/tests/test-agents-vault.fish
+++ b/tests/test-agents-vault.fish
@@ -310,6 +310,64 @@ check "link failure: no link was left behind" false (test -L $croot3/$mangled3/m
 set -e __fish_agent_vault_dir
 set -e __fish_agent_vault_claude_root
 
+#   ────────────────────────── slug migration ─────────────────────────────
+echo ""
+echo "== agents-vault (slug migration) =="
+
+set -l vroot2 (mktemp -d); set -ga TMPDIRS $vroot2
+set -l croot2 (mktemp -d); set -ga TMPDIRS $croot2
+set -g __fish_agent_vault_dir $vroot2/agent-vault
+set -g __fish_agent_vault_claude_root $croot2
+
+# Start with no remote, so the project is keyed local-*.
+set -l mp (new_repo)
+set -l mmangled (string replace -a '/' '-' -- $mp | string replace -a '.' '-')
+mkdir -p $croot2/$mmangled/memory
+echo "precious" >$croot2/$mmangled/memory/keep.md
+
+pushd $mp >/dev/null
+agents-vault --silent
+set -l local_slug (_agents_repo_slug $mp)
+popd >/dev/null
+check "local entry populated" precious (cat $vroot2/agent-vault/projects/$local_slug/claude/memory/keep.md)
+
+# Now add a remote: the slug changes and the entry must migrate.
+git -C $mp remote add origin https://git.rootiest.dev/rootiest/later.git
+pushd $mp >/dev/null
+agents-vault --silent
+popd >/dev/null
+set -l new_slug git.rootiest.dev-rootiest-later
+
+check "migrated to remote slug" precious (cat $vroot2/agent-vault/projects/$new_slug/claude/memory/keep.md)
+check "old entry removed" false (test -d $vroot2/agent-vault/projects/$local_slug; and echo true; or echo false)
+check "memory still reachable live" precious (cat $croot2/$mmangled/memory/keep.md)
+check "link repinned to new entry" (path resolve $vroot2/agent-vault/projects/$new_slug/claude/memory) (path resolve $croot2/$mmangled/memory)
+check "rename recorded in origin" true (grep -q "$local_slug" $vroot2/agent-vault/projects/$new_slug/origin; and echo true; or echo false)
+
+# Ambiguous migration: both entries hold content. Nothing may move.
+set -l amb (new_repo)
+set -l amangled (string replace -a '/' '-' -- $amb | string replace -a '.' '-')
+mkdir -p $croot2/$amangled/memory
+echo old >$croot2/$amangled/memory/x.md
+pushd $amb >/dev/null
+agents-vault --silent
+set -l aslug (_agents_repo_slug $amb)
+popd >/dev/null
+
+git -C $amb remote add origin https://git.rootiest.dev/rootiest/clash.git
+mkdir -p $vroot2/agent-vault/projects/git.rootiest.dev-rootiest-clash/claude/memory
+echo new >$vroot2/agent-vault/projects/git.rootiest.dev-rootiest-clash/claude/memory/y.md
+
+pushd $amb >/dev/null
+set -l arc (agents-vault --silent 2>/dev/null; echo $status)
+popd >/dev/null
+check "ambiguous migration fails" 1 "$arc"
+check "ambiguous leaves old entry" old (cat $vroot2/agent-vault/projects/$aslug/claude/memory/x.md)
+check "ambiguous leaves new entry" new (cat $vroot2/agent-vault/projects/git.rootiest.dev-rootiest-clash/claude/memory/y.md)
+
+set -e __fish_agent_vault_dir
+set -e __fish_agent_vault_claude_root
+
 cleanup
 echo ""
 echo (math $TESTS_RUN - $TESTS_FAILED)"/$TESTS_RUN passed"