Address Gadfly review on revision history

Six real bugs, three of which would have broken the feature's central promise.

The worst was that a failed operation threw away the history for changes that
had already committed. WithChangeSet buffers HISTORY, not data — the store
writes inside fn commit as they go — so discarding the buffer on error left real
mutations with no change set and no way to undo them. That is exactly the
situation undo exists for: an agent turn that did half a thing and then failed.
Now the buffer is written, the summary says the operation failed partway, and
the error is still returned. RevertChangeSet does the same for a revert that
fails mid-loop. The partial state is still partial, but it is visible and
undoable instead of orphaned.

versionGuard falsely conflicted whenever one change set held more than one
revision for the same entity — an agent turn that moves a bed and then renames
it. Each inverse bumps the row's version, so from the second one on the
snapshot's version no longer matched the live row and the revert flagged its own
work as somebody else's edit. RevertChangeSet now tracks what it has written and
the guard compares against that.

ListChangeSets found "was this reverted?" with a LEFT JOIN, which emits one
duplicate row per revert once a change set has been reverted more than once
(undo, redo, undo again). Now a scalar subquery.

Reverting an object creation cascade-deleted anything planted in that bed since,
quietly. The plops were snapshotted so it was recoverable, but deleting
someone's plants as a side effect of an unrelated undo should be reported. It
now conflicts and leaves the bed alone.

ClearObject cleared by predicate and snapshotted by a separate read, so a plop
created between the two was removed with no revision to undo it by. It now
clears exactly the ids it read. It also returned an error when only the
post-clear re-read failed, which told the caller a clear had failed after it had
already applied — inviting a retry of an applied operation. That path now logs
the history gap and reports success, matching how record() treats its own write
failures.

RestoreObject/RestorePlanting could lose the race between the existence check
and the insert and surface a raw constraint error. The revert now re-checks and
reports ConflictExists, which is what that condition means.

RevertChangeSet takes a source, so an agent undoing its own work is
distinguishable from a person clicking undo — the whole point of the badge.

Refactoring: the three revert bodies repeated a load/guard/unsnapshot/update
skeleton (flagged by 3 of 5 models). They are now one generic revertEntity over
a small per-type op table, so the ordering, guards and conflict reporting cannot
drift apart. The API's view structs duplicated domain types that already carried
every field, against the package's direct-JSON convention — dropped. intQuery
moved next to the other request helpers. planRevert's comment said three passes
where the code runs five. A revert where every revision is already a no-op now
answers 200 rather than 201 with a null change set.

Six new tests, one per bug.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

internal/store/plantings.go

@@ -102,15 +102,28 @@ func (d *DB) RestorePlanting(ctx context.Context, p *domain.Planting) (*domain.P
 	return restored, nil
 }
 
-// ClearObjectPlantings soft-removes every active plop in an object in one UPDATE
+// ClearObjectPlantings soft-removes the given plops of an object in one UPDATE
 // (sets removed_at=date, bumps version) and returns how many rows it affected.
-func (d *DB) ClearObjectPlantings(ctx context.Context, objectID int64, date string) (int, error) {
+//
+// It takes explicit ids rather than clearing "every active plop" so the caller
+// can snapshot exactly the rows it is about to change. Clearing by predicate
+// would let a plop created between the caller's read and this UPDATE be removed
+// without a revision — cleared, but with no way to undo it.
+func (d *DB) ClearObjectPlantings(ctx context.Context, objectID int64, date string, ids []int64) (int, error) {
+	if len(ids) == 0 {
+		return 0, nil
+	}
+	args := make([]any, 0, len(ids)+2)
+	args = append(args, date, objectID)
+	for _, id := range ids {
+		args = append(args, id)
+	}
 	res, err := d.sql.ExecContext(ctx,
 		`UPDATE plantings
 		    SET removed_at = ?, version = version + 1,
 		        updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
-		  WHERE object_id = ? AND removed_at IS NULL`,
-		date, objectID,
+		  WHERE object_id = ? AND removed_at IS NULL AND id IN (`+placeholders(len(ids))+`)`,
+		args...,
 	)
 	if err != nil {
 		return 0, fmt.Errorf("store: clear object plantings: %w", err)