Merge: group the frames of one moment, and let a burst fold away

FR-CULL-5. Frames join a burst when they are adjacent in time and look
like the frame before them -- both, because time alone groups a whole
ceremony and similarity alone groups a studio setup across two days.
Adjacent pairs only, chained; there is no all-pairs step and there must
never be one.

No selection of any kind. The representative is the earliest frame, a
fact about the clock rather than a judgement about the photograph, and a
newly found burst arrives open, so the pass never takes a row off the
screen.

Verified: fmt, clippy --workspace --all-targets -D warnings, 346
dr-catalog tests, 511 dr-ui tests.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

core/dr-catalog/src/lib.rs

@@ -16,6 +16,7 @@
 //! - [`collections`] — the collection tree and membership the UI edits
 //! - [`keywords`] — the keyword vocabulary and what it is assigned to
 //! - [`faces`] — detected faces, the people they belong to, and who said so
+//! - [`bursts`] — frames that are one moment, grouped so they judge as one
 //! - [`jobs`] — the durable background work queue
 //! - [`trash`] — soft delete to a folder, then permanent delete
 //! - [`merge`] / [`sync`] — cross-device merging of collections and keywords
@@ -33,6 +34,7 @@ use std::path::Path;
 use dr_types::{Availability, ImageId};
 use rusqlite::Connection;
 
+pub mod bursts;
 pub mod cache;
 pub mod collections;
 pub mod dedup;

core/dr-catalog/src/schema.rs

@@ -15,7 +15,7 @@ use rusqlite::Connection;
 use crate::error::CatalogError;
 
 /// Schema version this build writes and understands.
-pub const SCHEMA_VERSION: i64 = 10;
+pub const SCHEMA_VERSION: i64 = 11;
 
 /// Apply migrations up to [`SCHEMA_VERSION`].
 ///
@@ -98,6 +98,13 @@ pub fn migrate(conn: &Connection) -> Result<i64, CatalogError> {
         tx.commit()?;
     }
 
+    if from < 11 {
+        let tx = conn.unchecked_transaction()?;
+        tx.execute_batch(V11)?;
+        tx.pragma_update(None, "user_version", 11)?;
+        tx.commit()?;
+    }
+
     Ok(from)
 }
 
@@ -205,6 +212,11 @@ pub fn v1_for_attached(schema_name: &str) -> String {
 /// creating it over there would fail on columns that are not there. Nothing is
 /// lost by its absence — it exists to make the *grid* page quickly, and the
 /// grid never reads across an attachment.
+///
+/// V11 is excluded on the same grounds and for the plainer reason that a merge
+/// has nothing to do with it: burst grouping is rebuilt locally from local
+/// signatures, and no code reads a remote catalog's `burst_*` tables. Its
+/// `ALTER TABLE` would fail here anyway, being unqualifiable by the rewrite.
 pub fn for_attached(schema_name: &str) -> String {
     // V10 is `ALTER TABLE`, which the textual rewrite cannot qualify, so its
     // columns are spelled out. A remote genuinely older than V10 is a real
@@ -397,6 +409,73 @@ ALTER TABLE people ADD COLUMN ignored INTEGER NOT NULL DEFAULT 0;
 ALTER TABLE faces ADD COLUMN crop BLOB;
 "#;
 
+/// TRACES: FR-CULL-5
+/// Burst grouping: which frames are one moment, and which one stands for it.
+///
+/// The reasoning behind the grouping itself is in [`crate::bursts`]; what
+/// belongs here is why it is stored in three pieces rather than one.
+///
+/// **`images.perceptual_hash` is a column, not a table**, for the same reason
+/// `content_hash` is: it is one number per image, NULL until something has had
+/// the pixels in hand, and every query that wants it is already reading the
+/// image row. It is local derived state — a rebuilt catalog recomputes it from
+/// thumbnails — which is also why it is absent from [`for_attached`], alongside
+/// the shadowing and trashing columns V2 through V5 add.
+///
+/// **`burst_members` is rewritten whole by every pass.** No id of its own: the
+/// group is named by the image id of its earliest frame, so a burst that has not
+/// changed keeps its name across a regroup and the interface can remember that
+/// this one is open. There is no `bursts` table to go with it because a group
+/// has no properties beyond its members — inventing a row for it would create an
+/// identity that survives the grouping being rebuilt, which is precisely what
+/// must not happen.
+///
+/// **`burst_pick` is the one thing here that is not derived**, and it is a
+/// separate table so that rewriting the grouping cannot erase it. A
+/// representative stored on `burst_members` would be forgotten every time a
+/// frame arrived; the user would be asked the same question after every scan.
+/// The same argument `people.ignored` makes in V10, one subsystem over.
+///
+/// **`burst_expanded` is view state in the catalog**, which is unusual enough to
+/// justify. The grid is a window over an ordered query — `LIMIT n OFFSET k` —
+/// so what a collapsed burst hides has to be decided by the query, or the row
+/// count stops agreeing with the scrollbar and the ordinals a scrub resolves to.
+/// Once SQL has to see it, this is where it lives. Nothing else reads it, and it
+/// is emptied of stale groups by every pass.
+const V11: &str = r#"
+-- A 64-bit perceptual signature. Local derived state: NULL until something has
+-- decoded the image, recomputed from thumbnails if the catalog is rebuilt, and
+-- comparable only to signatures produced by the same build (`bursts`).
+ALTER TABLE images ADD COLUMN perceptual_hash INTEGER;
+
+CREATE TABLE burst_members (
+    -- One burst at most per image: a frame belongs to the moment it was taken
+    -- in, and nothing else.
+    image_id       INTEGER PRIMARY KEY REFERENCES images(id) ON DELETE CASCADE,
+    -- The image id of the burst's earliest frame. Not a foreign key by
+    -- accident: the leader is itself a member, so this genuinely references
+    -- images(id), and cascading its deletion is right.
+    burst_id       INTEGER NOT NULL REFERENCES images(id) ON DELETE CASCADE,
+    -- The frame the group collapses to. Exactly one per burst.
+    representative INTEGER NOT NULL DEFAULT 0
+);
+-- Counting a burst's frames and listing them are what the grid asks for, once
+-- per window; without this both are a scan of every grouped frame in the
+-- library.
+CREATE INDEX burst_members_burst ON burst_members(burst_id);
+
+-- The user's own choice of representative. User data, never rewritten by a
+-- grouping pass -- see the module doc above.
+CREATE TABLE burst_pick (
+    image_id INTEGER PRIMARY KEY REFERENCES images(id) ON DELETE CASCADE
+);
+
+-- Bursts the grid is currently showing in full.
+CREATE TABLE burst_expanded (
+    burst_id INTEGER PRIMARY KEY REFERENCES images(id) ON DELETE CASCADE
+);
+"#;
+
 const V9: &str = r#"
 -- TRACES: FR-CULL-8
 -- A record that face detection has *run* on an image, distinct from what it