diff --git a/src/bin/link_versions.rs b/src/bin/link_versions.rs
new file mode 100644
index 0000000..580d424
--- /dev/null
+++ b/src/bin/link_versions.rs
@@ -0,0 +1,225 @@
+//! Link photo versions that were ingested before linking existed (#191).
+//!
+//! **Default is a dry run**: nothing is written. It prints a TSV of every
+//! proposed link (`status method library_id version_path original_path
+//! phash_distance kind ...`) and a summary on stderr.
+//!
+//! - `exact` rows (the PNG's XMP `DerivedFrom` hash, or the
+//!   `<name>.<kind>[.<n>].<ext>` convention next to an indexed original) are
+//!   the same links the watcher makes at ingest; `--apply` writes them
+//!   without review.
+//! - `review` rows (ComfyUI prompt `LoadImage` input, Upscayl-style names,
+//!   nearest pHash) are heuristic. Save the dry-run output, delete the rows
+//!   you don't want, and pass the file as `--reviewed`; only those are
+//!   written, and each is checked against the database first so a stale file
+//!   can't link a path that now holds different bytes.
+//! - `unresolved` rows are listed, never guessed.
+//!
+//! `--apply` first takes a WAL-safe snapshot of the database
+//! (`VACUUM INTO`) and refuses to write if that fails. Prove it on a copy of
+//! the database first. The library roots are only ever read.
+
+use std::collections::HashSet;
+use std::path::PathBuf;
+use std::sync::{Arc, Mutex};
+
+use clap::Parser;
+use diesel::prelude::*;
+use diesel::sql_types::{BigInt, Integer, Nullable, Text};
+
+use image_api::database::version_dao::VersionDao;
+use image_api::database::{SqliteVersionDao, connect};
+use image_api::libraries;
+use image_api::versions::backfill::{self, FileRow, Status};
+
+#[derive(Parser, Debug)]
+#[command(name = "link_versions")]
+#[command(about = "Propose (dry run) or write links from photo versions to their originals")]
+struct Args {
+    /// Write the links. Without it nothing is changed.
+    #[arg(long)]
+    apply: bool,
+
+    /// A reviewed copy of the dry-run TSV: its `review` rows are linked too.
+    /// Only meaningful with --apply.
+    #[arg(long, value_name = "FILE")]
+    reviewed: Option<PathBuf>,
+
+    /// Directory for the pre-apply snapshot (default: next to the database).
+    #[arg(long, value_name = "DIR")]
+    backup_dir: Option<PathBuf>,
+
+    /// Only consider this library id (repeatable). Default: every library.
+    #[arg(long = "library", value_name = "ID")]
+    libraries: Vec<i32>,
+}
+
+#[derive(QueryableByName)]
+struct DbRow {
+    #[diesel(sql_type = Integer)]
+    library_id: i32,
+    #[diesel(sql_type = Text)]
+    rel_path: String,
+    #[diesel(sql_type = Text)]
+    content_hash: String,
+    #[diesel(sql_type = Nullable<BigInt>)]
+    phash_64: Option<i64>,
+}
+
+#[derive(QueryableByName)]
+struct Count {
+    #[diesel(sql_type = BigInt)]
+    n: i64,
+}
+
+#[derive(QueryableByName)]
+struct Hash {
+    #[diesel(sql_type = Text)]
+    version_hash: String,
+}
+
+fn main() -> anyhow::Result<()> {
+    env_logger::init();
+    dotenv::dotenv().ok();
+    let args = Args::parse();
+    if args.reviewed.is_some() && !args.apply {
+        anyhow::bail!("--reviewed only applies together with --apply (the default is a dry run)");
+    }
+
+    let mut conn = connect();
+    let has_table = diesel::sql_query(
+        "SELECT COUNT(*) AS n FROM sqlite_master WHERE type = 'table' AND name = 'photo_versions'",
+    )
+    .get_result::<Count>(&mut conn)?;
+    if has_table.n == 0 {
+        anyhow::bail!(
+            "this database has no photo_versions table; start the server once (it runs the \
+             migrations) or point DATABASE_URL at a migrated copy"
+        );
+    }
+
+    let mut libs = libraries::load_all(&mut conn);
+    if !args.libraries.is_empty() {
+        libs.retain(|l| args.libraries.contains(&l.id));
+    }
+    if libs.is_empty() {
+        anyhow::bail!("no matching libraries");
+    }
+    let lib_ids: HashSet<i32> = libs.iter().map(|l| l.id).collect();
+
+    let rows: Vec<FileRow> = diesel::sql_query(
+        "SELECT library_id, rel_path, content_hash, phash_64 FROM image_exif \
+         WHERE content_hash IS NOT NULL ORDER BY library_id, rel_path",
+    )
+    .load::<DbRow>(&mut conn)?
+    .into_iter()
+    .filter(|r| lib_ids.contains(&r.library_id))
+    .map(|r| FileRow {
+        library_id: r.library_id,
+        rel_path: r.rel_path,
+        content_hash: r.content_hash,
+        phash: r.phash_64,
+    })
+    .collect();
+    let linked: HashSet<String> = diesel::sql_query("SELECT version_hash FROM photo_versions")
+        .load::<Hash>(&mut conn)?
+        .into_iter()
+        .map(|h| h.version_hash)
+        .collect();
+
+    eprintln!(
+        "{} hashed image/video rows, {} version links already recorded",
+        rows.len(),
+        linked.len()
+    );
+    let proposals = backfill::plan(&libs, &rows, &linked);
+
+    println!("{}", backfill::TSV_HEADER);
+    for p in &proposals {
+        println!("{}", p.to_tsv());
+    }
+    let count = |s: Status| proposals.iter().filter(|p| p.status == s).count();
+    eprintln!(
+        "\nproposals: {} exact (apply without review), {} review (need --reviewed), {} unresolved",
+        count(Status::Exact),
+        count(Status::Review),
+        count(Status::Unresolved)
+    );
+    for method in ["xmp", "name", "comfy-loader", "name-prefix", "phash"] {
+        let n = proposals.iter().filter(|p| p.method == method).count();
+        if n > 0 {
+            eprintln!("  {method}: {n}");
+        }
+    }
+
+    if !args.apply {
+        eprintln!("dry run: nothing written. Re-run with --apply to write the exact links.");
+        return Ok(());
+    }
+
+    let reviewed = match &args.reviewed {
+        Some(path) => {
+            let text = std::fs::read_to_string(path)?;
+            let (links, skipped) = backfill::parse_reviewed(&text);
+            eprintln!(
+                "reviewed file: {} review row(s) to link, {} other line(s) ignored",
+                links.len(),
+                skipped
+            );
+            links
+        }
+        None => Vec::new(),
+    };
+
+    let backup = backup_database(&mut conn, args.backup_dir.as_deref())?;
+    eprintln!("snapshot written: {}", backup.display());
+    drop(conn);
+
+    let dao: Arc<Mutex<Box<dyn VersionDao>>> =
+        Arc::new(Mutex::new(Box::new(SqliteVersionDao::new())));
+    let mut guard = dao.lock().unwrap();
+    let report = backfill::apply(guard.as_mut(), &proposals, &reviewed, &rows);
+    let synced = guard
+        .sync_version_metadata()
+        .map_err(|e| anyhow::anyhow!("{e:?}"))?;
+    eprintln!(
+        "linked {} ({} already linked, {} refused, {} stale reviewed row(s)); \
+         date/GPS/camera copied onto {} version row(s)",
+        report.linked, report.already_linked, report.refused, report.stale, synced
+    );
+    Ok(())
+}
+
+/// Snapshot the live database with `VACUUM INTO`, which is consistent with
+/// the WAL (a plain file copy is not).
+fn backup_database(
+    conn: &mut diesel::SqliteConnection,
+    dir: Option<&std::path::Path>,
+) -> anyhow::Result<PathBuf> {
+    let url = dotenv::var("DATABASE_URL")?;
+    let db_path = PathBuf::from(url.trim_start_matches("sqlite://"));
+    let dir = match dir {
+        Some(d) => d.to_path_buf(),
+        None => db_path
+            .parent()
+            .filter(|p| !p.as_os_str().is_empty())
+            .map(PathBuf::from)
+            .unwrap_or_else(|| PathBuf::from(".")),
+    };
+    let stem = db_path
+        .file_name()
+        .map(|n| n.to_string_lossy().into_owned())
+        .unwrap_or_else(|| "database".into());
+    let target = dir.join(format!(
+        "{stem}.pre-link_versions-{}.bak",
+        chrono::Utc::now().format("%Y%m%dT%H%M%SZ")
+    ));
+    if target.exists() {
+        anyhow::bail!("{} already exists", target.display());
+    }
+    let escaped = target.to_string_lossy().replace('\'', "''");
+    diesel::sql_query(format!("VACUUM INTO '{escaped}'"))
+        .execute(conn)
+        .map_err(|e| anyhow::anyhow!("snapshot failed, nothing was written: {e}"))?;
+    Ok(target)
+}
diff --git a/src/versions/backfill.rs b/src/versions/backfill.rs
new file mode 100644
index 0000000..0d7af8b
--- /dev/null
+++ b/src/versions/backfill.rs
@@ -0,0 +1,931 @@
+//! Backfill of photo versions that were ingested before linking existed
+//! (the `link_versions` binary).
+//!
+//! Two kinds of proposal:
+//!
+//! - **Exact** (`xmp`, `name`): the PNG carries the producer's XMP
+//!   `DerivedFrom` hash, or its name follows `<name>.<kind>[.<n>].<ext>` next
+//!   to an indexed original. The ingest path would have made the same link,
+//!   so these apply without review.
+//! - **Review** (`comfy-loader`, `name-prefix`, `phash`): files with no XMP,
+//!   matched by the ComfyUI prompt's `LoadImage` input, an Upscayl-style
+//!   name, or the nearest pHash. Heuristic, so they only go through a TSV a
+//!   human has read (`--reviewed`). Ambiguous or unresolvable cases are
+//!   listed, never guessed.
+//!
+//! [`plan`] only reads (database rows handed in, library files for XMP and
+//! the prompt chunk); [`apply`] is the only writer and goes through
+//! [`VersionDao`].
+
+use std::collections::{HashMap, HashSet};
+use std::path::Path;
+use std::sync::LazyLock;
+
+use regex::Regex;
+
+use super::xmp::{self, XMP_KEYWORD};
+use super::{VERSIONS_SUBFOLDER, original_candidates, parse_version_name};
+use crate::database::version_dao::{
+    LinkOutcome, NewVersionLink, SOURCE_BACKFILL, SOURCE_NAME, SOURCE_XMP, VersionDao,
+    is_known_kind,
+};
+use crate::file_types;
+use crate::libraries::Library;
+
+/// A nearest-pHash match farther than this (of 64 bits) is not proposed.
+pub const MAX_PHASH_DISTANCE: u32 = 16;
+
+/// One `image_exif` row, as far as planning needs it.
+#[derive(Debug, Clone)]
+pub struct FileRow {
+    pub library_id: i32,
+    pub rel_path: String,
+    pub content_hash: String,
+    pub phash: Option<i64>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Status {
+    /// Applies without review.
+    Exact,
+    /// Heuristic; applies only from a reviewed TSV.
+    Review,
+    /// Listed, not guessed.
+    Unresolved,
+}
+
+impl Status {
+    fn as_str(self) -> &'static str {
+        match self {
+            Status::Exact => "exact",
+            Status::Review => "review",
+            Status::Unresolved => "unresolved",
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Proposal {
+    pub status: Status,
+    /// `xmp` | `name` | `comfy-loader` | `name-prefix` | `phash`
+    pub method: &'static str,
+    pub library_id: i32,
+    pub version_path: String,
+    pub version_hash: String,
+    /// Empty for an unresolved case, or an XMP link whose original isn't indexed.
+    pub original_path: String,
+    pub original_hash: String,
+    pub kind: String,
+    pub distance: Option<u32>,
+    /// Hashes of reference photos (the other loader inputs).
+    pub references: Vec<String>,
+    pub notes: String,
+}
+
+pub const TSV_HEADER: &str = "status\tmethod\tlibrary_id\tversion_path\toriginal_path\tphash_distance\tkind\tversion_hash\toriginal_hash\treferences\tnotes";
+
+impl Proposal {
+    pub fn to_tsv(&self) -> String {
+        let clean = |s: &str| s.replace(['\t', '\n', '\r'], " ");
+        [
+            self.status.as_str().to_string(),
+            self.method.to_string(),
+            self.library_id.to_string(),
+            clean(&self.version_path),
+            clean(&self.original_path),
+            self.distance.map(|d| d.to_string()).unwrap_or_default(),
+            self.kind.clone(),
+            self.version_hash.clone(),
+            self.original_hash.clone(),
+            self.references.join(","),
+            clean(&self.notes),
+        ]
+        .join("\t")
+    }
+}
+
+/// A row of a reviewed TSV: just enough to link.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ReviewedLink {
+    pub method: String,
+    pub library_id: i32,
+    pub version_path: String,
+    pub kind: String,
+    pub version_hash: String,
+    pub original_hash: String,
+    pub references: Vec<String>,
+}
+
+/// Parse a reviewed TSV (the dry-run output with rows deleted or kept).
+/// Rows that aren't `review` status with both hashes are skipped; so are the
+/// header, blanks and `#` comments. Returns `(links, skipped_lines)`.
+pub fn parse_reviewed(tsv: &str) -> (Vec<ReviewedLink>, usize) {
+    let mut out = Vec::new();
+    let mut skipped = 0;
+    for line in tsv.lines() {
+        if line.trim().is_empty() || line.starts_with('#') || line.starts_with("status\t") {
+            continue;
+        }
+        let f: Vec<&str> = line.split('\t').collect();
+        let usable = f.len() >= 10
+            && f[0] == "review"
+            && f[2].parse::<i32>().is_ok()
+            && !f[7].is_empty()
+            && !f[8].is_empty();
+        if !usable {
+            skipped += 1;
+            continue;
+        }
+        out.push(ReviewedLink {
+            method: f[1].to_string(),
+            library_id: f[2].parse().unwrap(),
+            version_path: f[3].to_string(),
+            kind: f[6].to_string(),
+            version_hash: f[7].to_string(),
+            original_hash: f[8].to_string(),
+            references: f[9]
+                .split(',')
+                .filter(|s| !s.is_empty())
+                .map(str::to_string)
+                .collect(),
+        });
+    }
+    (out, skipped)
+}
+
+fn dir_of(rel: &str) -> &str {
+    rel.rsplit_once('/').map_or("", |(d, _)| d)
+}
+
+fn name_of(rel: &str) -> &str {
+    rel.rsplit('/').next().unwrap_or(rel)
+}
+
+fn parent_of_dir(dir: &str) -> &str {
+    dir.rsplit_once('/').map_or("", |(p, _)| p)
+}
+
+fn is_aiedits_dir(dir: &str) -> bool {
+    name_of(dir).eq_ignore_ascii_case(VERSIONS_SUBFOLDER)
+}
+
+/// Names that are themselves versions (convention or Upscayl output) are
+/// never proposed as someone's original.
+fn looks_like_a_version(file_name: &str) -> bool {
+    parse_version_name(file_name).is_some() || upscayl_stem(file_name).is_some()
+}
+
+fn hamming(a: i64, b: i64) -> u32 {
+    ((a ^ b) as u64).count_ones()
+}
+
+static UPSCAYL_SUFFIX: LazyLock<Regex> = LazyLock::new(|| {
+    // `<name>-4x.png`, `<name>_upscayl_2x_ultramix_balanced.png`
+    Regex::new(r"(?i)^(?P<stem>.+?)(?:-\d+x|_upscayl_\d+(?:\.\d+)?x_[^.]+)\.png$").unwrap()
+});
+
+fn upscayl_stem(file_name: &str) -> Option<String> {
+    UPSCAYL_SUFFIX
+        .captures(file_name)
+        .map(|c| c["stem"].to_string())
+}
+
+/// File names a ComfyUI prompt loads, in node order: the `image` input of
+/// every `LoadImage*` node.
+pub fn loader_names(prompt_json: &str) -> Vec<String> {
+    let Ok(value) = serde_json::from_str::<serde_json::Value>(prompt_json) else {
+        return Vec::new();
+    };
+    let Some(nodes) = value.as_object() else {
+        return Vec::new();
+    };
+    let mut ids: Vec<&String> = nodes.keys().collect();
+    ids.sort_by_key(|k| k.parse::<u64>().unwrap_or(u64::MAX));
+    let mut out = Vec::new();
+    for id in ids {
+        let node = &nodes[id];
+        let class = node["class_type"].as_str().unwrap_or("");
+        if !class.starts_with("LoadImage") {
+            continue;
+        }
+        if let Some(raw) = node["inputs"]["image"].as_str() {
+            let name = raw.trim_end_matches(" [input]");
+            let name = name.rsplit(['/', '\\']).next().unwrap_or(name);
+            if !name.is_empty() {
+                out.push(name.to_string());
+            }
+        }
+    }
+    out
+}
+
+struct Index<'a> {
+    by_path: HashMap<(i32, &'a str), &'a FileRow>,
+    by_name: HashMap<(i32, &'a str), Vec<&'a FileRow>>,
+    by_dir: HashMap<(i32, &'a str), Vec<&'a FileRow>>,
+}
+
+impl<'a> Index<'a> {
+    fn new(rows: &'a [FileRow]) -> Self {
+        let mut idx = Index {
+            by_path: HashMap::new(),
+            by_name: HashMap::new(),
+            by_dir: HashMap::new(),
+        };
+        for r in rows {
+            idx.by_path.insert((r.library_id, r.rel_path.as_str()), r);
+            idx.by_name
+                .entry((r.library_id, name_of(&r.rel_path)))
+                .or_default()
+                .push(r);
+            idx.by_dir
+                .entry((r.library_id, dir_of(&r.rel_path)))
+                .or_default()
+                .push(r);
+        }
+        idx
+    }
+}
+
+/// Plan every link the backfill can propose. `rows` are all hashed image
+/// rows; `linked` the version hashes that already have a link.
+pub fn plan(libs: &[Library], rows: &[FileRow], linked: &HashSet<String>) -> Vec<Proposal> {
+    let idx = Index::new(rows);
+    let root_of: HashMap<i32, &str> = libs.iter().map(|l| (l.id, l.root_path.as_str())).collect();
+    let mut out = Vec::new();
+
+    for row in rows {
+        if linked.contains(&row.content_hash) {
+            continue;
+        }
+        let name = name_of(&row.rel_path);
+        let dir = dir_of(&row.rel_path);
+        let is_png = name.to_ascii_lowercase().ends_with(".png");
+        let name_conv = parse_version_name(name);
+        let upscayl = if is_png { upscayl_stem(name) } else { None };
+        let in_aiedits = is_aiedits_dir(dir);
+        if !(is_png || name_conv.is_some()) {
+            continue;
+        }
+        if !file_types::is_image_file(Path::new(&row.rel_path)) {
+            continue;
+        }
+
+        // Text chunks (XMP + ComfyUI prompt) of PNGs, read once.
+        let mut xmp_text = None;
+        let mut prompt = None;
+        if is_png && let Some(root) = root_of.get(&row.library_id) {
+            let abs = Path::new(root).join(&row.rel_path);
+            if let Ok(chunks) = xmp::read_png_text(&abs, &[XMP_KEYWORD, "prompt"]) {
+                for (k, v) in chunks {
+                    if k == XMP_KEYWORD {
+                        xmp_text = Some(v);
+                    } else {
+                        prompt = Some(v);
+                    }
+                }
+            }
+        }
+
+        // 1. XMP: exact, even when the original isn't indexed yet.
+        if let Some(x) = xmp_text.as_deref().and_then(xmp::parse_version_xmp)
+            && x.original_hash != row.content_hash
+        {
+            let original = rows.iter().find(|r| r.content_hash == x.original_hash);
+            let kind = x
+                .kind
+                .filter(|k| is_known_kind(k))
+                .or_else(|| name_conv.as_ref().map(|n| n.kind.to_string()))
+                .unwrap_or_else(|| "edit".to_string());
+            out.push(Proposal {
+                status: Status::Exact,
+                method: "xmp",
+                library_id: row.library_id,
+                version_path: row.rel_path.clone(),
+                version_hash: row.content_hash.clone(),
+                original_path: original.map(|o| o.rel_path.clone()).unwrap_or_default(),
+                original_hash: x.original_hash,
+                kind,
+                distance: distance(row, original),
+                references: x.references,
+                notes: if original.is_some() {
+                    String::new()
+                } else {
+                    "original not indexed (yet)".into()
+                },
+            });
+            continue;
+        }
+
+        // 2. Name convention next to an indexed original: exact.
+        if let Some(n) = &name_conv {
+            let found = original_candidates(&row.rel_path)
+                .into_iter()
+                .find_map(|c| {
+                    idx.by_path
+                        .get(&(row.library_id, c.as_str()))
+                        .copied()
+                        .filter(|o| o.content_hash != row.content_hash)
+                });
+            if let Some(o) = found {
+                out.push(Proposal {
+                    status: Status::Exact,
+                    method: "name",
+                    library_id: row.library_id,
+                    version_path: row.rel_path.clone(),
+                    version_hash: row.content_hash.clone(),
+                    original_path: o.rel_path.clone(),
+                    original_hash: o.content_hash.clone(),
+                    kind: n.kind.to_string(),
+                    distance: distance(row, Some(o)),
+                    references: Vec::new(),
+                    notes: String::new(),
+                });
+                continue;
+            }
+            // A convention name with no original found falls through to the
+            // heuristics only if it is also a ComfyUI output in aiedits/.
+            if !in_aiedits {
+                out.push(unresolved(row, "name", "no original with that name nearby"));
+                continue;
+            }
+        }
+
+        // 3. Heuristics (PNG only; reviewed before applying).
+        if !is_png {
+            continue;
+        }
+        let loaders = prompt.as_deref().map(loader_names).unwrap_or_default();
+        if in_aiedits && !loaders.is_empty() {
+            out.push(plan_comfy_loader(row, &loaders, &idx));
+        } else if let Some(stem) = upscayl {
+            out.push(plan_prefix(row, &stem, &idx));
+        } else if in_aiedits {
+            out.push(plan_phash(row, rows));
+        }
+    }
+    out.sort_by(|a, b| {
+        (a.status as u8, a.library_id, &a.version_path).cmp(&(
+            b.status as u8,
+            b.library_id,
+            &b.version_path,
+        ))
+    });
+    out
+}
+
+fn distance(version: &FileRow, original: Option<&FileRow>) -> Option<u32> {
+    Some(hamming(version.phash?, original?.phash?))
+}
+
+fn unresolved(row: &FileRow, method: &'static str, why: &str) -> Proposal {
+    Proposal {
+        status: Status::Unresolved,
+        method,
+        library_id: row.library_id,
+        version_path: row.rel_path.clone(),
+        version_hash: row.content_hash.clone(),
+        original_path: String::new(),
+        original_hash: String::new(),
+        kind: "edit".into(),
+        distance: None,
+        references: Vec::new(),
+        notes: why.to_string(),
+    }
+}
+
+/// Nearest row to `row` by pHash among `candidates` (needs both hashes).
+fn nearest<'a>(row: &FileRow, candidates: &[&'a FileRow]) -> Option<(&'a FileRow, u32)> {
+    let p = row.phash?;
+    candidates
+        .iter()
+        .filter_map(|c| Some((*c, hamming(p, c.phash?))))
+        .min_by_key(|(c, d)| (*d, c.rel_path.clone()))
+}
+
+fn plan_comfy_loader(row: &FileRow, loaders: &[String], idx: &Index) -> Proposal {
+    let dir = dir_of(&row.rel_path);
+    let parent = parent_of_dir(dir);
+    // Per loader name: the matching rows from the first tier that has any,
+    // preferring the parent of aiedits/, then the same folder, then anywhere
+    // in the library. Version-looking files never count as originals.
+    let resolve = |loader: &str| -> Vec<&FileRow> {
+        let all: Vec<&FileRow> = idx
+            .by_name
+            .get(&(row.library_id, loader))
+            .map(|v| {
+                v.iter()
+                    .copied()
+                    .filter(|r| {
+                        r.content_hash != row.content_hash && !is_aiedits_dir(dir_of(&r.rel_path))
+                    })
+                    .collect()
+            })
+            .unwrap_or_default();
+        for tier in [parent, dir] {
+            let hit: Vec<&FileRow> = all
+                .iter()
+                .copied()
+                .filter(|r| dir_of(&r.rel_path) == tier)
+                .collect();
+            if !hit.is_empty() {
+                return hit;
+            }
+        }
+        all
+    };
+
+    let mut resolved: Vec<(&String, Vec<&FileRow>)> = Vec::new();
+    let mut missing: Vec<&String> = Vec::new();
+    for l in loaders {
+        let hits = resolve(l);
+        if hits.is_empty() {
+            missing.push(l);
+        } else {
+            resolved.push((l, hits));
+        }
+    }
+    if resolved.is_empty() {
+        let mut p = unresolved(
+            row,
+            "comfy-loader",
+            &format!(
+                "loader input(s) not found in the library: {}",
+                loaders.join(", ")
+            ),
+        );
+        // A hint for the reviewer, not a proposal.
+        let siblings: Vec<&FileRow> = idx
+            .by_dir
+            .get(&(row.library_id, parent))
+            .map(|v| {
+                v.iter()
+                    .copied()
+                    .filter(|r| !is_aiedits_dir(dir_of(&r.rel_path)))
+                    .collect()
+            })
+            .unwrap_or_default();
+        if let Some((n, d)) = nearest(row, &siblings) {
+            p.notes
+                .push_str(&format!("; hint: nearest pHash {} (d={d})", n.rel_path));
+        }
+        return p;
+    }
+
+    // Primary: the nearest pHash across everything the loaders resolved to.
+    let flat: Vec<(&String, &FileRow)> = resolved
+        .iter()
+        .flat_map(|(l, hits)| hits.iter().map(move |h| (*l, *h)))
+        .collect();
+    let rows_only: Vec<&FileRow> = flat.iter().map(|(_, r)| *r).collect();
+    let (primary, dist) = match nearest(row, &rows_only) {
+        Some((p, d)) => (p, Some(d)),
+        None => (rows_only[0], None),
+    };
+    let mut notes = Vec::new();
+    if resolved.len() > 1 {
+        notes.push("two loader inputs: primary chosen by nearest pHash, the other recorded as a reference — check".to_string());
+    }
+    if flat.len() > resolved.len() {
+        notes.push("a loader name matched several files — check".into());
+    }
+    if !missing.is_empty() {
+        notes.push(format!(
+            "other loader input(s) not in the library: {}",
+            missing
+                .iter()
+                .map(|s| s.as_str())
+                .collect::<Vec<_>>()
+                .join(", ")
+        ));
+    }
+    if dist.is_none() {
+        notes.push("no pHash to compare".into());
+    }
+    let mut references: Vec<String> = Vec::new();
+    for (_, hits) in &resolved {
+        for h in hits {
+            if h.content_hash != primary.content_hash && !references.contains(&h.content_hash) {
+                references.push(h.content_hash.clone());
+            }
+        }
+    }
+    Proposal {
+        status: Status::Review,
+        method: "comfy-loader",
+        library_id: row.library_id,
+        version_path: row.rel_path.clone(),
+        version_hash: row.content_hash.clone(),
+        original_path: primary.rel_path.clone(),
+        original_hash: primary.content_hash.clone(),
+        kind: "edit".into(),
+        distance: dist,
+        references,
+        notes: notes.join("; "),
+    }
+}
+
+fn plan_prefix(row: &FileRow, stem: &str, idx: &Index) -> Proposal {
+    let dir = dir_of(&row.rel_path);
+    let matches: Vec<&FileRow> = idx
+        .by_dir
+        .get(&(row.library_id, dir))
+        .map(|v| {
+            v.iter()
+                .copied()
+                .filter(|r| {
+                    r.content_hash != row.content_hash
+                        && name_of(&r.rel_path)
+                            .rsplit_once('.')
+                            .is_some_and(|(s, _)| s == stem)
+                })
+                .collect()
+        })
+        .unwrap_or_default();
+    match matches.as_slice() {
+        [] => unresolved(
+            row,
+            "name-prefix",
+            &format!("no file named {stem}.* beside it"),
+        ),
+        [only] => Proposal {
+            status: Status::Review,
+            method: "name-prefix",
+            library_id: row.library_id,
+            version_path: row.rel_path.clone(),
+            version_hash: row.content_hash.clone(),
+            original_path: only.rel_path.clone(),
+            original_hash: only.content_hash.clone(),
+            kind: "upscale".into(),
+            distance: distance(row, Some(only)),
+            references: Vec::new(),
+            notes: String::new(),
+        },
+        several => {
+            let (best, d) = nearest(row, several).unwrap_or((several[0], u32::MAX));
+            Proposal {
+                status: Status::Review,
+                method: "name-prefix",
+                library_id: row.library_id,
+                version_path: row.rel_path.clone(),
+                version_hash: row.content_hash.clone(),
+                original_path: best.rel_path.clone(),
+                original_hash: best.content_hash.clone(),
+                kind: "upscale".into(),
+                distance: (d != u32::MAX).then_some(d),
+                references: Vec::new(),
+                notes: format!("{} files share that name — check", several.len()),
+            }
+        }
+    }
+}
+
+fn plan_phash(row: &FileRow, rows: &[FileRow]) -> Proposal {
+    let dir = dir_of(&row.rel_path);
+    let parent = parent_of_dir(dir);
+    let candidates: Vec<&FileRow> = rows
+        .iter()
+        .filter(|r| {
+            r.library_id == row.library_id
+                && r.content_hash != row.content_hash
+                && !is_aiedits_dir(dir_of(&r.rel_path))
+                && !looks_like_a_version(name_of(&r.rel_path))
+                && (dir_of(&r.rel_path) == parent || dir_of(&r.rel_path) == dir)
+        })
+        .collect();
+    match nearest(row, &candidates) {
+        Some((o, d)) if d <= MAX_PHASH_DISTANCE => Proposal {
+            status: Status::Review,
+            method: "phash",
+            library_id: row.library_id,
+            version_path: row.rel_path.clone(),
+            version_hash: row.content_hash.clone(),
+            original_path: o.rel_path.clone(),
+            original_hash: o.content_hash.clone(),
+            kind: "edit".into(),
+            distance: Some(d),
+            references: Vec::new(),
+            notes: "matched by nearest pHash only".into(),
+        },
+        Some((o, d)) => unresolved(
+            row,
+            "phash",
+            &format!("nearest pHash is {} at distance {d}, too far", o.rel_path),
+        ),
+        None => unresolved(row, "phash", "no pHash candidates nearby"),
+    }
+}
+
+/// What [`apply`] did.
+#[derive(Debug, Default, PartialEq, Eq)]
+pub struct ApplyReport {
+    pub linked: usize,
+    pub already_linked: usize,
+    pub refused: usize,
+    /// Reviewed rows whose version row no longer matches the file in the TSV.
+    pub stale: usize,
+}
+
+/// Write the links. `exact` proposals apply as they are; `reviewed` come
+/// from a TSV a human kept, and are checked against `rows` first so a stale
+/// file can't link a path that now holds different bytes.
+pub fn apply(
+    dao: &mut dyn VersionDao,
+    exact: &[Proposal],
+    reviewed: &[ReviewedLink],
+    rows: &[FileRow],
+) -> ApplyReport {
+    let mut report = ApplyReport::default();
+    let current: HashMap<(i32, &str), &str> = rows
+        .iter()
+        .map(|r| ((r.library_id, r.rel_path.as_str()), 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 {
+            version_hash: p.version_hash.clone(),
+            original_hash: p.original_hash.clone(),
+            kind: p.kind.clone(),
+            source: if p.method == "xmp" {
+                SOURCE_XMP
+            } else {
+                SOURCE_NAME
+            }
+            .to_string(),
+            library_id: p.library_id,
+            rel_path: p.version_path.clone(),
+            references: p.references.clone(),
+        });
+    }
+    for r in reviewed {
+        if current.get(&(r.library_id, r.version_path.as_str())) != Some(&r.version_hash.as_str()) {
+            report.stale += 1;
+            continue;
+        }
+        links.push(NewVersionLink {
+            version_hash: r.version_hash.clone(),
+            original_hash: r.original_hash.clone(),
+            kind: if is_known_kind(&r.kind) {
+                r.kind.clone()
+            } else {
+                "edit".into()
+            },
+            source: SOURCE_BACKFILL.to_string(),
+            library_id: r.library_id,
+            rel_path: r.version_path.clone(),
+            references: r.references.clone(),
+        });
+    }
+    for link in links {
+        match dao.link_version(&link) {
+            Ok(LinkOutcome::Linked) => report.linked += 1,
+            Ok(LinkOutcome::AlreadyLinked) => report.already_linked += 1,
+            Ok(LinkOutcome::Rejected(_)) | Err(_) => report.refused += 1,
+        }
+    }
+    report
+}
+
+#[cfg(test)]
+mod tests {
+    use super::super::xmp::test_png::{producer_xmp, write_png};
+    use super::*;
+    use crate::database::SqliteVersionDao;
+    use crate::database::test::in_memory_db_connection;
+    use std::sync::{Arc, Mutex};
+
+    fn row(rel: &str, hash: &str, phash: Option<i64>) -> FileRow {
+        FileRow {
+            library_id: 1,
+            rel_path: rel.into(),
+            content_hash: hash.into(),
+            phash,
+        }
+    }
+
+    fn lib(root: &Path) -> Library {
+        Library {
+            id: 1,
+            name: "main".into(),
+            root_path: root.to_string_lossy().into(),
+            enabled: true,
+            excluded_dirs: vec![],
+        }
+    }
+
+    fn prompt(loaders: &[&str]) -> String {
+        let mut nodes = serde_json::Map::new();
+        nodes.insert(
+            "1".into(),
+            serde_json::json!({"class_type": "UNETLoader", "inputs": {"unet_name": "m"}}),
+        );
+        for (i, l) in loaders.iter().enumerate() {
+            nodes.insert(
+                (i + 2).to_string(),
+                serde_json::json!({"class_type": "LoadImage", "inputs": {"image": l}}),
+            );
+        }
+        serde_json::Value::Object(nodes).to_string()
+    }
+
+    fn write_comfy_png(root: &Path, rel: &str, loaders: &[&str], salt: u8) {
+        super::super::xmp::test_png::write_png(&root.join(rel), None, Some(&prompt(loaders)), salt);
+    }
+
+    #[test]
+    fn loader_names_reads_only_loadimage_inputs_in_node_order() {
+        let p = prompt(&["a.jpg", "sub/b [input]"]);
+        assert_eq!(loader_names(&p), vec!["a.jpg", "b"]);
+        assert!(loader_names("not json").is_empty());
+    }
+
+    #[test]
+    fn already_ingested_xmp_files_are_proposed_as_exact_without_naming_help() {
+        let tmp = tempfile::tempdir().unwrap();
+        let orig_hash = "d5".repeat(32);
+        write_png(
+            &tmp.path().join("2009/aiedits/019_19.JPG.restored.png"),
+            Some(&producer_xmp(&orig_hash, "restored", &[])),
+            None,
+            1,
+        );
+        // An XMP file whose name gives no hint (a renamed copy).
+        write_png(
+            &tmp.path().join("misc/renamed.png"),
+            Some(&producer_xmp(
+                &orig_hash,
+                "upscale",
+                &["ee".repeat(32).as_str()],
+            )),
+            None,
+            2,
+        );
+        let rows = vec![
+            row("2009/019_19.JPG", &orig_hash, None),
+            row("2009/aiedits/019_19.JPG.restored.png", "v1", None),
+            row("misc/renamed.png", "v2", None),
+        ];
+        let plan = plan(&[lib(tmp.path())], &rows, &HashSet::new());
+        let by_path: HashMap<&str, &Proposal> =
+            plan.iter().map(|p| (p.version_path.as_str(), p)).collect();
+        let a = by_path["2009/aiedits/019_19.JPG.restored.png"];
+        assert_eq!((a.status, a.method), (Status::Exact, "xmp"));
+        assert_eq!(a.original_path, "2009/019_19.JPG");
+        let b = by_path["misc/renamed.png"];
+        assert_eq!(
+            (b.status, b.method, b.kind.as_str()),
+            (Status::Exact, "xmp", "upscale")
+        );
+        assert_eq!(b.references.len(), 1);
+    }
+
+    #[test]
+    fn comfy_outputs_are_resolved_by_loader_and_flagged_when_two_inputs() {
+        let tmp = tempfile::tempdir().unwrap();
+        write_comfy_png(tmp.path(), "Amanda/aiedits/out_00001_.png", &["a.jpg"], 1);
+        write_comfy_png(
+            tmp.path(),
+            "Amanda/aiedits/out_00002_.png",
+            &["a.jpg", "b.jpg"],
+            2,
+        );
+        write_comfy_png(
+            tmp.path(),
+            "Amanda/aiedits/out_00003_.png",
+            &["typo.jpg"],
+            3,
+        );
+        let rows = vec![
+            row("Amanda/a.jpg", "ha", Some(0b1111)),
+            row("Amanda/b.jpg", "hb", Some(-1)),
+            row("Amanda/aiedits/out_00001_.png", "v1", Some(0b1110)),
+            row("Amanda/aiedits/out_00002_.png", "v2", Some(0b1011)),
+            row("Amanda/aiedits/out_00003_.png", "v3", Some(0)),
+        ];
+        let plan = plan(&[lib(tmp.path())], &rows, &HashSet::new());
+        let get = |p: &str| plan.iter().find(|x| x.version_path == p).unwrap();
+
+        let one = get("Amanda/aiedits/out_00001_.png");
+        assert_eq!((one.status, one.method), (Status::Review, "comfy-loader"));
+        assert_eq!(one.original_path, "Amanda/a.jpg");
+        assert_eq!(one.distance, Some(1));
+        assert!(one.references.is_empty());
+
+        let two = get("Amanda/aiedits/out_00002_.png");
+        assert_eq!(
+            two.original_path, "Amanda/a.jpg",
+            "primary by nearest pHash"
+        );
+        assert_eq!(two.references, vec!["hb"]);
+        assert!(two.notes.contains("two loader inputs"));
+
+        let lost = get("Amanda/aiedits/out_00003_.png");
+        assert_eq!(lost.status, Status::Unresolved);
+        assert!(lost.original_path.is_empty(), "listed, not guessed");
+    }
+
+    #[test]
+    fn upscayl_names_and_phash_fallback() {
+        let tmp = tempfile::tempdir().unwrap();
+        write_png(&tmp.path().join("p/att_1-4x.png"), None, None, 1);
+        write_png(
+            &tmp.path().join("p/pic_upscayl_3x_ultramix_balanced.png"),
+            None,
+            None,
+            2,
+        );
+        write_png(&tmp.path().join("p/aiedits/mystery.png"), None, None, 3);
+        let rows = vec![
+            row("p/att_1.jpg", "h1", Some(5)),
+            row("p/pic.jpeg", "h2", Some(5)),
+            row("p/other.jpg", "h3", Some(0b0111_1111_1111)),
+            row("p/att_1-4x.png", "u1", Some(5)),
+            row("p/pic_upscayl_3x_ultramix_balanced.png", "u2", Some(5)),
+            row("p/aiedits/mystery.png", "m1", Some(7)),
+        ];
+        let plan = plan(&[lib(tmp.path())], &rows, &HashSet::new());
+        let get = |p: &str| plan.iter().find(|x| x.version_path == p).unwrap();
+        assert_eq!(get("p/att_1-4x.png").original_path, "p/att_1.jpg");
+        assert_eq!(get("p/att_1-4x.png").kind, "upscale");
+        assert_eq!(
+            get("p/pic_upscayl_3x_ultramix_balanced.png").original_path,
+            "p/pic.jpeg"
+        );
+        let m = get("p/aiedits/mystery.png");
+        assert_eq!(m.method, "phash");
+        assert_eq!(m.status, Status::Review);
+        assert_eq!(
+            m.original_path, "p/att_1.jpg",
+            "distance 2 beats the others"
+        );
+    }
+
+    #[test]
+    fn linked_rows_are_not_proposed_again() {
+        let tmp = tempfile::tempdir().unwrap();
+        write_png(&tmp.path().join("a.jpg.restored.png"), None, None, 1);
+        let rows = vec![
+            row("a.jpg", "o", None),
+            row("a.jpg.restored.png", "v", None),
+        ];
+        let linked = HashSet::from(["v".to_string()]);
+        assert!(plan(&[lib(tmp.path())], &rows, &linked).is_empty());
+        let p = plan(&[lib(tmp.path())], &rows, &HashSet::new());
+        assert_eq!((p[0].status, p[0].method), (Status::Exact, "name"));
+    }
+
+    #[test]
+    fn tsv_round_trip_and_reviewed_application() {
+        let tmp = tempfile::tempdir().unwrap();
+        write_comfy_png(tmp.path(), "d/aiedits/o_00001_.png", &["a.jpg", "b.jpg"], 1);
+        let rows = vec![
+            row("d/a.jpg", "ha", Some(1)),
+            row("d/b.jpg", "hb", Some(-1)),
+            row("d/aiedits/o_00001_.png", "v", Some(1)),
+            row("d/x.jpg", "hx", None),
+            row("d/x.jpg.edit.png", "vx", None),
+        ];
+        write_png(&tmp.path().join("d/x.jpg.edit.png"), None, None, 9);
+        let planned = plan(&[lib(tmp.path())], &rows, &HashSet::new());
+        let tsv: String = std::iter::once(TSV_HEADER.to_string())
+            .chain(planned.iter().map(Proposal::to_tsv))
+            .collect::<Vec<_>>()
+            .join("\n");
+        let (reviewed, skipped) = parse_reviewed(&tsv);
+        assert_eq!(
+            reviewed.len(),
+            1,
+            "only the review row; the exact one isn't re-applied from the file"
+        );
+        assert_eq!(skipped, 1);
+        assert_eq!(reviewed[0].references, vec!["hb"]);
+
+        let conn = Arc::new(Mutex::new(in_memory_db_connection()));
+        let mut dao = SqliteVersionDao::from_shared(conn);
+        // Without --reviewed: exact only.
+        let report = apply(&mut dao, &planned, &[], &rows);
+        assert_eq!(report.linked, 1);
+        assert!(dao.get_link("vx").unwrap().is_some());
+        assert!(
+            dao.get_link("v").unwrap().is_none(),
+            "heuristic rows never auto-apply"
+        );
+        // With the reviewed file.
+        let report = apply(&mut dao, &planned, &reviewed, &rows);
+        assert_eq!(report.linked, 1);
+        assert_eq!(report.already_linked, 1);
+        let l = dao.get_link("v").unwrap().unwrap();
+        assert_eq!(
+            (l.original_hash.as_str(), l.source.as_str()),
+            ("ha", "backfill")
+        );
+        assert_eq!(dao.list_references("v").unwrap(), vec!["hb"]);
+
+        // A stale TSV (the path now holds other bytes) is refused.
+        let mut stale_rows = rows.clone();
+        stale_rows[2].content_hash = "changed".into();
+        let report = apply(&mut dao, &[], &reviewed, &stale_rows);
+        assert_eq!(report.stale, 1);
+    }
+}
diff --git a/src/versions/mod.rs b/src/versions/mod.rs
index 1100890..2ef7803 100644
--- a/src/versions/mod.rs
+++ b/src/versions/mod.rs
@@ -14,6 +14,7 @@
 //! original's `content_hash`, never a path: ComfyUI writes through a UNC
 //! share and ImageApi reads `/media/...`, and files get moved.
 
+pub mod backfill;
 pub mod handlers;
 pub mod xmp;