Validate original_hash in link_versions --reviewed; document follow-ups (#194)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/versions/backfill.rs

@@ -110,6 +110,8 @@ pub struct ReviewedLink {
     pub method: String,
     pub library_id: i32,
     pub version_path: String,
+    /// The original's path as the dry run proposed it (may be empty).
+    pub original_path: String,
     pub kind: String,
     pub version_hash: String,
     pub original_hash: String,
@@ -140,6 +142,7 @@ pub fn parse_reviewed(tsv: &str) -> (Vec<ReviewedLink>, usize) {
             method: f[1].to_string(),
             library_id: f[2].parse().unwrap(),
             version_path: f[3].to_string(),
+            original_path: f[4].to_string(),
             kind: f[6].to_string(),
             version_hash: f[7].to_string(),
             original_hash: f[8].to_string(),
@@ -634,6 +637,8 @@ pub struct ApplyReport {
     pub refused: usize,
     /// Reviewed rows whose version row no longer matches the file in the TSV.
     pub stale: usize,
+    /// One line per stale reviewed row, saying what no longer matches.
+    pub stale_details: Vec<String>,
 }
 
 /// Write the links. `exact` proposals apply as they are; `reviewed` come
@@ -651,6 +656,8 @@ pub fn apply(
         .map(|r| ((r.library_id, r.rel_path.as_str()), r.content_hash.as_str()))
         .collect();
 
+    let live_hashes: HashSet<&str> = rows.iter().map(|r| r.content_hash.as_str()).collect();
+
     let mut links: Vec<NewVersionLink> = Vec::new();
     for p in exact.iter().filter(|p| p.status == Status::Exact) {
         links.push(NewVersionLink {
@@ -669,8 +676,32 @@ pub fn apply(
         });
     }
     for r in reviewed {
-        if current.get(&(r.library_id, r.version_path.as_str())) != Some(&r.version_hash.as_str()) {
+        let stale = if current.get(&(r.library_id, r.version_path.as_str()))
+            != Some(&r.version_hash.as_str())
+        {
+            Some("version file now holds different bytes (or is gone)")
+        } else if !live_hashes.contains(r.original_hash.as_str()) {
+            Some("original_hash is not in the index any more")
+        } else if !r.original_path.is_empty()
+            && current
+                .get(&(r.library_id, r.original_path.as_str()))
+                .is_some_and(|h| *h != r.original_hash.as_str())
+        {
+            Some("original path now holds different bytes than original_hash")
+        } else {
+            None
+        };
+        if let Some(why) = stale {
             report.stale += 1;
+            report.stale_details.push(format!(
+                "{} -> {}: {why}",
+                r.version_path,
+                if r.original_path.is_empty() {
+                    &r.original_hash
+                } else {
+                    &r.original_path
+                }
+            ));
             continue;
         }
         links.push(NewVersionLink {
@@ -977,6 +1008,19 @@ mod tests {
         stale_rows[2].content_hash = "changed".into();
         let report = apply(&mut dao, &[], &reviewed, &stale_rows);
         assert_eq!(report.stale, 1);
+
+        // So is one whose original changed since the dry run: its hash is
+        // gone from the index, or its path holds other bytes.
+        let mut gone = rows.clone();
+        gone[0].content_hash = "ha-edited".into();
+        let report = apply(&mut dao, &[], &reviewed, &gone);
+        assert_eq!(report.stale, 1);
+        assert_eq!(report.linked + report.already_linked, 0);
+        assert!(report.stale_details[0].contains("d/aiedits/o_00001_.png"));
+        let mut swapped = rows.clone();
+        swapped[0].content_hash = "hb".into(); // d/a.jpg now holds hb's bytes
+        let report = apply(&mut dao, &[], &reviewed, &swapped);
+        assert_eq!(report.stale, 1);
     }
     #[test]
     fn apply_drops_derived_data_of_an_already_ingested_version() {
@@ -1000,11 +1044,13 @@ mod tests {
             method: "phash".into(),
             library_id: 1,
             version_path: "v.png".into(),
+            original_path: "o.jpg".into(),
             kind: "edit".into(),
             version_hash: "v".into(),
             original_hash: "o".into(),
             references: vec![],
         }];
+        let rows = vec![row("v.png", "v", None), row("o.jpg", "o", None)];
         assert_eq!(apply(&mut dao, &[], &reviewed, &rows).linked, 1);
 
         #[derive(diesel::QueryableByName)]