diff --git a/desktop/src-tauri/src/managed_agents/library.rs b/desktop/src-tauri/src/managed_agents/library.rs
index 16e7edab4..7360d898d 100644
--- a/desktop/src-tauri/src/managed_agents/library.rs
+++ b/desktop/src-tauri/src/managed_agents/library.rs
@@ -588,5 +588,91 @@ fn identity_collisions<'a>(
     colliders
 }
 
+// ── §2.5 pure identity-binding helpers ────────────────────────────────────────
+
+impl LibraryDocument {
+    /// The §2.5 deletion-protection predicate (P13-C1, widened by P17-C1):
+    /// answers, purely from `library.json`, whether the key for `agent_pubkey`
+    /// must NEVER be deleted or its identity archived in v1. `true` iff ANY
+    /// entry — live or tombstoned, any `deleted` value, any projection state —
+    /// has EVER bound this pubkey, OR any outstanding `deferred_archives` row
+    /// names it. Every removal path (direct delete, persona cascade, inbound
+    /// kind:5, forced delete, §3.4/§3.5 cascades, the finalizer, every recovery
+    /// point) MUST consult this for the record's pubkey before `delete_agent_key`
+    /// or NIP-IA archival, regardless of the record's own linkage — the keyring
+    /// is process-global by pubkey, so an unrelated plain carrier of a bound
+    /// pubkey would otherwise destroy the binding's one global identity.
+    ///
+    /// Scans the RAW entries (not the decoded healthy set) so a QUARANTINED
+    /// entry that names the pubkey still protects it: mis-deleting a live key is
+    /// catastrophic and irreversible, while over-protecting only leaves a secret
+    /// resident — the v1 posture is conservative by design. Ever-bound is
+    /// observable forever because tombstoned entries and their binding records
+    /// are kept forever (P1-OQ2).
+    pub fn key_archive_protected(&self, agent_pubkey: &str) -> bool {
+        self.entries
+            .iter()
+            .any(|entry| entry_names_agent(entry, agent_pubkey))
+    }
+}
+
+/// Whether one raw entry `Value` binds `agent_pubkey` in `identity_bindings` or
+/// carries an outstanding `deferred_archives` row for it (§2.5). Field-name
+/// exact matches on the raw JSON so a quarantined entry still counts.
+fn entry_names_agent(entry: &Value, agent_pubkey: &str) -> bool {
+    let bound = entry
+        .get("identity_bindings")
+        .and_then(Value::as_object)
+        .is_some_and(|bindings| {
+            bindings
+                .values()
+                .any(|b| b.get("agent_pubkey").and_then(Value::as_str) == Some(agent_pubkey))
+        });
+    if bound {
+        return true;
+    }
+    entry
+        .get("deferred_archives")
+        .and_then(Value::as_array)
+        .is_some_and(|rows| {
+            rows.iter()
+                .any(|r| r.get("agent_pubkey").and_then(Value::as_str) == Some(agent_pubkey))
+        })
+}
+
+/// One linked instance's identity coordinates for §2.5 seed selection.
+pub(crate) struct SeedCandidate<'a> {
+    /// ISO-8601 UTC creation timestamp — same format for every record, so
+    /// lexical order equals chronological order.
+    pub created_at: &'a str,
+    pub pubkey: &'a str,
+}
+
+/// Deterministic binding-seed selection (§2.5, P3-I2): among the linked
+/// instances that exist at share/first-deploy time, the seed is the instance
+/// with the earliest `created_at`, ties broken by the lowest pubkey — the
+/// longest-lived identity collaborators are most likely to know. `None` is
+/// legal ONLY when zero instances exist (no identity to carry yet; the first
+/// deploy anywhere seeds the binding). The chosen pubkey is what carries across
+/// the owner's scopes; the others keep their identities locally, unchanged.
+///
+/// Pure selection only; the caller performs the §2.5 mint/verify protocol on
+/// the result inside the insertion transaction (P8-C2, Phase 4b).
+pub(crate) fn select_binding_seed<'a>(
+    instances: impl IntoIterator<Item = SeedCandidate<'a>>,
+) -> Option<&'a str> {
+    instances
+        .into_iter()
+        .min_by(|a, b| {
+            a.created_at
+                .cmp(b.created_at)
+                .then_with(|| a.pubkey.cmp(b.pubkey))
+        })
+        .map(|winner| winner.pubkey)
+}
+
 #[cfg(test)]
 mod tests;
+
+#[cfg(test)]
+mod binding_tests;
diff --git a/desktop/src-tauri/src/managed_agents/library/binding_tests.rs b/desktop/src-tauri/src/managed_agents/library/binding_tests.rs
new file mode 100644
index 000000000..b954677b1
--- /dev/null
+++ b/desktop/src-tauri/src/managed_agents/library/binding_tests.rs
@@ -0,0 +1,149 @@
+//! Phase-3 §2.5 pure identity-binding helper tests: the `key_archive_protected`
+//! deletion-safety predicate (P13-C1/P17-C1) and deterministic `select_binding_seed`
+//! (P3-I2). Both are keyring-free pure functions; the crash-safe mint protocol and
+//! their transaction wiring land later (Phase 4b). Kept in their own module so the
+//! Phase-1 `tests.rs` suite stays clear of the 1000-line file ratchet.
+
+use serde_json::json;
+
+use super::*;
+
+// ── key_archive_protected ──────────────────────────────────────────────────────
+
+/// A raw entry `Value` binding `agent_pubkey` under one owner, with the given
+/// `deleted` tombstone flag. Only the fields the predicate reads are populated —
+/// the predicate scans raw entries, so a partial value is a faithful stand-in
+/// for both a healthy and a quarantined on-disk entry. The owner map key is a
+/// fixed placeholder: the predicate reads binding values, never the key.
+fn bound_entry(agent_pubkey: &str, deleted: bool) -> serde_json::Value {
+    json!({
+        "deleted": deleted,
+        "identity_bindings": {
+            "owner-key-placeholder": { "agent_pubkey": agent_pubkey, "auth_tag": "{}" }
+        }
+    })
+}
+
+fn deferred_entry(agent_pubkey: &str) -> serde_json::Value {
+    json!({
+        "deferred_archives": [ { "scope_id": "scope-1", "agent_pubkey": agent_pubkey } ]
+    })
+}
+
+fn library(entries: Vec<serde_json::Value>) -> LibraryDocument {
+    LibraryDocument {
+        version: SUPPORTED_LIBRARY_VERSION,
+        entries,
+        orphan_keys: vec![],
+    }
+}
+
+#[test]
+fn test_ever_bound_live_entry_protects_key() {
+    let target = "aa".repeat(32);
+    let doc = library(vec![bound_entry(&target, false)]);
+    assert!(doc.key_archive_protected(&target));
+}
+
+#[test]
+fn test_ever_bound_tombstoned_entry_still_protects_key() {
+    // Tombstones are kept forever (P1-OQ2); a deleted entry that once bound the
+    // pubkey must keep protecting it — the global keyring identity outlives the
+    // tombstone.
+    let target = "bb".repeat(32);
+    let doc = library(vec![bound_entry(&target, true)]);
+    assert!(doc.key_archive_protected(&target));
+}
+
+#[test]
+fn test_quarantined_entry_binding_pubkey_protects_key() {
+    // A structurally invalid entry (would be quarantined on decode) that still
+    // names the pubkey in identity_bindings must protect it: the predicate scans
+    // RAW entries so quarantine can never strip protection.
+    let target = "cc".repeat(32);
+    let garbage = json!({
+        "not_a_real_field": 7,
+        "identity_bindings": {
+            "owner-key-placeholder": { "agent_pubkey": target, "auth_tag": "{}" }
+        }
+    });
+    let doc = library(vec![garbage]);
+    assert!(doc.key_archive_protected(&target));
+}
+
+#[test]
+fn test_outstanding_deferred_archive_protects_key() {
+    // A deferred-archive obligation with no surviving binding must still protect:
+    // the retirement marker is the record that the key was never archived.
+    let target = "dd".repeat(32);
+    let doc = library(vec![deferred_entry(&target)]);
+    assert!(doc.key_archive_protected(&target));
+}
+
+#[test]
+fn test_unrelated_entry_does_not_protect_key() {
+    let target = "ee".repeat(32);
+    let other = "11".repeat(32);
+    let doc = library(vec![bound_entry(&other, false), deferred_entry(&other)]);
+    assert!(!doc.key_archive_protected(&target));
+}
+
+#[test]
+fn test_empty_library_protects_nothing() {
+    let doc = library(vec![]);
+    assert!(!doc.key_archive_protected(&"22".repeat(32)));
+}
+
+// ── select_binding_seed ─────────────────────────────────────────────────────────
+
+#[test]
+fn test_seed_picks_earliest_created() {
+    let seed = select_binding_seed(vec![
+        SeedCandidate {
+            created_at: "2026-08-11T10:00:00Z",
+            pubkey: "aaa",
+        },
+        SeedCandidate {
+            created_at: "2026-08-11T09:00:00Z",
+            pubkey: "bbb",
+        },
+        SeedCandidate {
+            created_at: "2026-08-11T11:00:00Z",
+            pubkey: "ccc",
+        },
+    ]);
+    assert_eq!(seed, Some("bbb"));
+}
+
+#[test]
+fn test_seed_breaks_created_tie_by_lowest_pubkey() {
+    let seed = select_binding_seed(vec![
+        SeedCandidate {
+            created_at: "2026-08-11T09:00:00Z",
+            pubkey: "ffff",
+        },
+        SeedCandidate {
+            created_at: "2026-08-11T09:00:00Z",
+            pubkey: "0001",
+        },
+        SeedCandidate {
+            created_at: "2026-08-11T09:00:00Z",
+            pubkey: "abcd",
+        },
+    ]);
+    assert_eq!(seed, Some("0001"));
+}
+
+#[test]
+fn test_seed_single_instance() {
+    let seed = select_binding_seed(vec![SeedCandidate {
+        created_at: "2026-08-11T09:00:00Z",
+        pubkey: "solo",
+    }]);
+    assert_eq!(seed, Some("solo"));
+}
+
+#[test]
+fn test_seed_empty_is_none() {
+    assert_eq!(select_binding_seed(Vec::new()), None);
+}