feat(lang): 27.3 - a reducer on a table's row: reducer T in S.table on A, @Target, Row<T>, @RowVerb, @Column

An action names one row of a ludic.base Table<T> by its handle, in a field marked @Target, and
`reducer Deer in Herd.deer on Spook(r: mut Row<Deer>, n: Noise, a: Spook)` runs once, for that row
alone (the table may sit down a path, S.w.tab). The drain resolves the handle (tb_row) and hands the
reducer a Row<T> - new in ludic.base: tb, row, h, rec - that the queue keeps, one per row reducer,
filled in place, so a targeted action allocates nothing; a stale handle runs nothing, and
LUDIC_ACTIONS_LOG=1 prints a line for it (@alloc_ok). Row reducers order among an action's by their
state's name, then the table's path.

Checked at compile time (actions_rows.ludic): the row reaches r.rec and r.h only - r.tb / r.row
refused, the view never assigned, stored, copied or handed on except to a @RowVerb (a function of
the record's own module taking Row<T> first; any other function taking a row is refused); a field
marked @Column (a table column mirrors it) is not written through r.rec; only the module owning the
state declares a row reducer; one @Target, an int, per action; the states between the row and the
action are read. `mut` is allowed on a Row<T> parameter.

ludic schema's code section gains row_reducers (record, table, state, action, target, predicted,
net, module, at) and row_verbs (name, record, module, at), and every action its target; row
reducers are left out of `reducers`. ludic deps and ludic-lsp name a row reducer
`reducer Deer in Herd.deer on Spook`. vocab: @Target, @Column, @RowVerb; docs/language pages;
LANGUAGE.md "A reducer on a row"; examples actions/rows and ten rejects; test.ludic feat, reject and
schema cases (not run); changes/row-reducers.md. Reseeded; bootstrap-cfree fixpoint holds (307497
lines); Maroon Lake's `ludic build --check` is clean against this tree.

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

selfhost/backend/emit_schema_code.ludic

@@ -4,6 +4,9 @@
 #   modules    name, package, layer, uses (null without a `uses` line) and where, friend, files
 #   states     name, module, at                    actions   name, module, at
 #   reducers   state, action, module, at           dispatch  action, module, at
+#   row_reducers  record, table (State.path), state, action, target (its @Target field), predicted,
+#              net, module, at                     row_verbs  name, record, module, at (27.3)
+#   actions also carry their target: the @Target field, or null
 #   events     name, module, at, cancellable, net (@ToServer / @ToClients), emits (sites) and
 #              listeners (the @On handlers: handler, module, at)
 #   ports      name, module, at, bound, members (name, type, default as written, required)
@@ -67,6 +70,10 @@ function sc_code(b: Buf) -> void {
   cx_decls(b, 3)
   buf_puts(b, "\n    ],\n    \"reducers\": [")
   cx_reducers(b)
+  buf_puts(b, "\n    ],\n    \"row_reducers\": [")
+  cx_row_reducers(b)
+  buf_puts(b, "\n    ],\n    \"row_verbs\": [")
+  cx_row_verbs(b)
   buf_puts(b, "\n    ],\n    \"dispatch\": [")
   cx_dispatch(b)
   buf_puts(b, "\n    ],\n    \"events\": [")
@@ -244,6 +251,10 @@ function cx_decls(b: Buf, uns: int) -> void {
     cx_module(b, d.file)
     buf_puts(b, ", ")
     cx_at(b, d)
+    if uns == 3 {                                 # an action: the field naming its row (27.3)
+      buf_puts(b, ", \"target\": ")
+      sc_str(b, rr_target(d.s))
+    }
     buf_puts(b, "}")
     i += 1
   }
@@ -253,7 +264,7 @@ function cx_reducers(b: Buf) -> void {
   var i = 0
   while i < len(g_red_nodes) {
     let f = g_red_nodes[i]
-    if cx_written(f) { push(keys, `{g_red_state[i]}\t{g_red_action[i]}\t{cx_at_key(f)}`) } else { push(keys, null) }
+    if cx_written(f) and g_red_rec[i] == null { push(keys, `{g_red_state[i]}\t{g_red_action[i]}\t{cx_at_key(f)}`) } else { push(keys, null) }
     i += 1
   }
   let xs = cx_order(keys)
@@ -274,6 +285,64 @@ function cx_reducers(b: Buf) -> void {
     i += 1
   }
 }
+# 27.3: the reducers on a table's rows, and the verbs that write a row
+function cx_row_reducers(b: Buf) -> void {
+  let keys = new []pointer
+  var i = 0
+  while i < len(g_red_nodes) {
+    let f = g_red_nodes[i]
+    if cx_written(f) and g_red_rec[i] != null { push(keys, `{g_red_rec[i]}\t{g_red_state[i]}.{g_red_tbl[i]}\t{g_red_action[i]}\t{cx_at_key(f)}`) } else { push(keys, null) }
+    i += 1
+  }
+  let xs = cx_order(keys)
+  i = 0
+  while i < len(xs) {
+    let k = xs[i]
+    let f = g_red_nodes[k]
+    sc_sep(b, i == 0, "      ")
+    buf_puts(b, "{\"record\": ")
+    jq_put(b, g_red_rec[k])
+    buf_puts(b, ", \"table\": ")
+    jq_put(b, `{g_red_state[k]}.{g_red_tbl[k]}`)
+    buf_puts(b, ", \"state\": ")
+    jq_put(b, g_red_state[k])
+    buf_puts(b, ", \"action\": ")
+    jq_put(b, g_red_action[k])
+    buf_puts(b, ", \"target\": ")
+    sc_str(b, g_red_tgt[k])
+    buf_puts(b, ", \"predicted\": false, \"net\": null, ")   # @Predicted and @Net come with 27.5
+    cx_module(b, f.file)
+    buf_puts(b, ", ")
+    cx_at(b, f)
+    buf_puts(b, "}")
+    i += 1
+  }
+}
+function cx_row_verbs(b: Buf) -> void {
+  let keys = new []pointer
+  var i = 0
+  while i < len(g_rv_nodes) {
+    let f = g_rv_nodes[i]
+    if cx_written(f) { push(keys, sc_key(f.s, f.file, f.line)) } else { push(keys, null) }
+    i += 1
+  }
+  let xs = cx_order(keys)
+  i = 0
+  while i < len(xs) {
+    let f = g_rv_nodes[xs[i]]
+    sc_sep(b, i == 0, "      ")
+    buf_puts(b, "{\"name\": ")
+    jq_put(b, f.s)
+    buf_puts(b, ", \"record\": ")
+    sc_str(b, rv_record(f))
+    buf_puts(b, ", ")
+    cx_module(b, f.file)
+    buf_puts(b, ", ")
+    cx_at(b, f)
+    buf_puts(b, "}")
+    i += 1
+  }
+}
 function cx_dispatch(b: Buf) -> void {
   let keys = new []pointer
   var i = 0

selfhost/backend/emit_vis.ludic

@@ -48,7 +48,7 @@ function vis_check(d: Node, what0: pointer) -> void {
   # 0.S/0.R: a state's instance, the action queue and a reducer are the runtime's to supply and to
   # call - the code that names them depends on no module for it
   if d.kind == N_VAR and d.uns == 1 and str_prefix(d.s, "state$") and is_state_ty(d.ty) { return }
-  if d.kind == N_FN and (str_prefix(d.s, "ludic_reduce__") or is_action_builtin(d.s)) { return }
+  if d.kind == N_FN and (str_prefix(d.s, "ludic_reduce__") or str_prefix(d.s, "ludic_rowred__") or is_action_builtin(d.s)) { return }
   deps_edge(d, what0)                            # LUDIC_DEPS: the graph ludic deps reads (emit_deps.ludic)
   if g_vis_off { return }
   if d.file == null { return }