Pin that Self and Persona social cache reads never write their stores

The re-pin swapped load_envelope for put_envelope on the claim that each
site's cache has no store attached, so put_envelope stays memory-only.
No existing test observed that: attaching the store in state_cache left
every resident_self test passing, because re-pushing the envelope just
read rewrites identical bytes.

Each test seeds its store, sets the file's modified time to a fixed past
instant, reopens the cache and requires the time to be unchanged. Any
push replaces the file through a staged rename, so attaching a store to
state_cache or persona_social_cache now fails the matching test. The
retirement-receipt site takes a snapshot slice with no path, so it cannot
acquire a store without a signature change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

epiphany-core/src/persona_social_state.rs

@@ -891,3 +891,36 @@ fn stable_pending_mention_id(
 fn now_iso() -> String {
     chrono::Utc::now().to_rfc3339()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn persona_social_cache_reads_without_writing_the_store() -> Result<()> {
+        let temp = tempfile::tempdir()?;
+        let store = temp.path().join("social.cc");
+        let cache = persona_social_cache(&store)?;
+        let head = PersonaSocialRetentionHeadDocument {
+            head: PersonaConversationRetentionHead::default(),
+        };
+        SingleFileMessagePackBackingStore::new(&store).push(
+            &cache
+                .prepare_entry(PERSONA_SOCIAL_RETENTION_HEAD_KEY, &head)?
+                .0,
+        )?;
+        let past = std::time::UNIX_EPOCH + std::time::Duration::from_secs(1_000_000_000);
+        std::fs::File::options()
+            .write(true)
+            .open(&store)?
+            .set_modified(past)?;
+        let reopened = persona_social_cache(&store)?;
+        assert_eq!(
+            reopened
+                .get::<PersonaSocialRetentionHeadDocument>(PERSONA_SOCIAL_RETENTION_HEAD_KEY)?,
+            Some(head)
+        );
+        assert_eq!(std::fs::metadata(&store)?.modified()?, past);
+        Ok(())
+    }
+}

epiphany-core/src/resident_self.rs

@@ -2730,6 +2730,31 @@ mod pressure_replay_tests {
         Ok(())
     }
 
+    #[test]
+    fn state_cache_reads_without_writing_the_store() -> Result<()> {
+        let temp = tempfile::tempdir()?;
+        let store = temp.path().join("resident.cc");
+        let cache = state_cache(&store)?;
+        SingleFileMessagePackBackingStore::new(&store).push(
+            &cache
+                .prepare_entry(RESIDENT_SELF_STATE_KEY, &ResidentSelfState::default())?
+                .0,
+        )?;
+        let past = std::time::UNIX_EPOCH + std::time::Duration::from_secs(1_000_000_000);
+        std::fs::File::options()
+            .write(true)
+            .open(&store)?
+            .set_modified(past)?;
+        let reopened = state_cache(&store)?;
+        assert!(
+            reopened
+                .get::<ResidentSelfState>(RESIDENT_SELF_STATE_KEY)?
+                .is_some()
+        );
+        assert_eq!(std::fs::metadata(&store)?.modified()?, past);
+        Ok(())
+    }
+
     #[test]
     fn configured_operator_pressure_replay_preserves_the_first_document() -> Result<()> {
         let temp = tempfile::tempdir()?;