feat(lang): 27.1 - a state machine as data: @Machine(Record.field) on a registry of transitions

A registry marked `@Machine(Deer.mood)` is the transitions of a machine over that enum field of the
records a state's Table<Deer> holds. Its record has from and to (the enum's variants), on: string (an
action's name, "" for a transition the tick asks), guard: fn(Row<Deer>, reads...) -> bool and
enter: fn(Row<Deer>, reads...) -> void; the states are the enum's variants and the start is the
field's default. The rows are data (an .lres or defs), the names the studio already edits.

Written by the compiler (machines.ludic, machines_write.ludic): for each action an `on` names, a row
reducer in the registry's file (named ..__machine__DeerSteps, so it sits beside the program's own
row reducer on the same action, after it): the row's state, the first transition from it on that
action whose guard passes, the field set, enter run - guards and enters called by name. When a row
leaves a state on a guard alone, `state DeerStepsMachine` (the kept row view) and
deer_steps_tick(m: mut DeerStepsMachine, s: mut Herd, reads...), one transition a row a tick.
Nothing allocates.

The table is the whole machine: the field written anywhere else - an assignment, or a `machine`
block's become over it - is a type error (check_stmt.ludic, ck_machine_write). Guards and enters take
the row first, are the record's module's, keep a row reducer's rules (and may be handed the row);
a guard writes nothing through it. The graph is checked, each error at its row (in the .lres when
the rows are there): a state never reached from the start, a state with no way out, an `on` naming
no action or an action with no @Target, a self-transition with no guard, two ways out of a state on
one trigger behind an unguarded first. Also refused: @Machine off a registry, a field that is not a
plain enum with a default, a @Column field, no table (or two) of the record, a transitions record of
another shape, a machine outside its table's state's module.

ludic schema's code section gains `machines` (registry, record, field, enum, table, start, states,
actions, tick, module, at); ludic deps names a machine's reducer `reducer Deer in Herd.deer on Spook
(machine DeerSteps)`. vocab @Machine; docs annot-machine, kw-machine; LANGUAGE.md "A machine as
data"; examples actions/machine (+ deer_steps.lres) and ten rejects; test.ludic feat, reject and
schema cases (not run); changes/machines.md. Reseeded; bootstrap-cfree fixpoint holds (317642
lines); Maroon Lake's `ludic build --check` is clean against this tree.

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

tools/docgen/inventory.json

@@ -41,6 +41,7 @@
     "annot-target",
     "annot-column",
     "annot-rowverb",
+    "annot-machine",
     "annot-permap",
     "annot-range",
     "annot-ref",

tools/ludic-cli/deps.ludic

@@ -269,8 +269,20 @@ function dp_fn_name(n: pointer) -> pointer {
   }
   return n
 }
-# 27.3: a row reducer's symbol says `Deer__in__Herd__deer` for `Deer in Herd.deer`
-function dp_row_name(s: pointer) -> pointer {
+# 27.3: a row reducer's symbol says `Deer__in__Herd__deer` for `Deer in Herd.deer`; one a @Machine
+# wrote ends `__machine__DeerSteps` (27.1)
+function dp_row_name(s0: pointer) -> pointer {
+  var s = s0
+  var tail = ""
+  var k = 0
+  while k + 11 <= slen(s0) {
+    if s0[k .. k + 11] == "__machine__" {
+      s = s0[0 .. k]
+      tail = ` (machine {s0[k + 11 .. slen(s0)]})`
+      break
+    }
+    k += 1
+  }
   var out = ""
   var seen = false
   var i = 0
@@ -287,7 +299,7 @@ function dp_row_name(s: pointer) -> pointer {
       i += 1
     }
   }
-  return out
+  return out + tail
 }
 function dp_own(k: int) -> bool { return dp_pkg[k] == 0 }
 # an edge the numbers count: between two of the program's own modules

tools/ludic-cli/selfhost.ludic

@@ -30,6 +30,8 @@ function selfhost_frags() -> []pointer {
   push(f, "selfhost/frontend/state.ludic")
   push(f, "selfhost/frontend/actions.ludic")
   push(f, "selfhost/frontend/actions_rows.ludic")
+  push(f, "selfhost/frontend/machines.ludic")
+  push(f, "selfhost/frontend/machines_write.ludic")
   push(f, "selfhost/frontend/migrate.ludic")
   push(f, "selfhost/frontend/registry.ludic")
   push(f, "selfhost/frontend/registry_finish.ludic")

tools/ludic-cli/test.ludic

@@ -1252,6 +1252,17 @@ function cmd_dev_test() -> int {
   reject_case("rejected/row_reducer_writes_state", "a row reducer writes its row alone, and n is a mut Noise", "a row reducer writes no state")
   reject_case("rejected/rowverb_no_row", "@RowVerb scare: a row verb takes the row first", "a @RowVerb takes its row first")
   reject_case("rejected/row_reducer_owner", "Herd is module herd's, and this reducer is in the program", "only the state's module reduces its table's rows")
+  feat_case("actions/machine", "", "0 0 1 1", "machine.ludic (27.1: @Machine - a state machine as data: the reducer on Spook, first match by guard, enter, and the tick's guard-only transitions)")
+  reject_case("rejected/machine_unreachable", "Mood.Fled is never reached from the start, Mood.Calm", "every state of a machine is reached from its start")
+  reject_case("rejected/machine_no_way_out", "Mood.Fled has no way out", "every state of a machine has a way out")
+  reject_case("rejected/machine_on_unknown", "on: \"Spok\" names no action", "a machine's on names an action")
+  reject_case("rejected/machine_on_no_target", "on: \"Shout\" names no row", "a machine's action names its row with @Target")
+  reject_case("rejected/machine_self_no_guard", "a transition from Wary to itself with no guard", "a self-transition has a guard")
+  reject_case("rejected/machine_ambiguous", "settles and stays both leave Wary on Spook, and settles has no guard", "one trigger, one unguarded way out")
+  reject_case("rejected/machine_guard_writes", "guard deer_nervous asks and changes nothing", "a machine's guard writes nothing through its row")
+  reject_case("rejected/machine_field_written", "Deer.mood is the machine DeerSteps's (@Machine(Deer.mood))", "a machine's field changes only by a transition in its table")
+  reject_case("rejected/machine_not_registry", "@Machine(Deer.mood) marks the registry of a machine's transitions", "@Machine is on a registry")
+  reject_case("rejected/machine_not_enum", "Deer.mood is int - a machine's state is a plain enum", "a machine's state is an enum field")
   feat_case("state/counter", "", "11 3 heard 5", "counter.ludic (0.S: a state, mut and read-only parameters, entry, listener and fn-value injection)")
   feat_case("state/port_field", "", "40", "port_field.ludic (0.S: a port member bound to a state's field)")
   spec_case("state/tested", "== 2 passed, 0 failed ==")
@@ -1373,6 +1384,7 @@ function cmd_dev_test() -> int {
   schema_case("actions/modules", "{\"action\": \"PickUp\", \"module\": null, \"at\": \"examples/actions/modules.ludic:8:21\"}", "--emit-schema: code.dispatch - every dispatch site")
   schema_case("actions/rows", "{\"record\": \"Deer\", \"table\": \"Herd.deer\", \"state\": \"Herd\", \"action\": \"Spook\", \"target\": \"who\", \"predicted\": false, \"net\": null, \"module\": null, \"at\": \"examples/actions/rows.ludic:17:32\"}", "--emit-schema: code.row_reducers - a row reducer's record, table, action and target")
   schema_case("actions/rows", "{\"name\": \"deer_move\", \"record\": \"Deer\", \"module\": null, \"at\": \"examples/actions/rows.ludic:24:21\"}", "--emit-schema: code.row_verbs - a @RowVerb and its record")
+  schema_case("actions/machine", "{\"registry\": \"DeerSteps\", \"record\": \"Deer\", \"field\": \"mood\", \"enum\": \"Mood\", \"table\": \"Herd.deer\", \"start\": \"Calm\", \"states\": [\"Calm\", \"Wary\", \"Fled\"], \"actions\": [\"Spook\"], \"tick\": \"deer_steps_tick\", \"module\": null, \"at\": \"examples/actions/machine.ludic:28:32\"}", "--emit-schema: code.machines - a @Machine's registry, field, enum, table, start, actions and tick")
   schema_case("actions/rows", "{\"name\": \"Spook\", \"module\": null, \"at\": \"examples/actions/rows.ludic:14:10\", \"target\": \"who\"}", "--emit-schema: code.actions - an action's @Target field")
   schema_case("modules/ports", "{\"name\": \"Clock\", \"module\": \"clock\", \"at\": \"examples/modules/station/clock/index.ludic:4:13\", \"bound\": true, \"members\": [{\"name\": \"now\", \"type\": \"fn()->int\", \"default\": null, \"required\": true}, {\"name\": \"day\", \"type\": \"fn()->int\", \"default\": \"fn first_day\", \"required\": false}]}", "--emit-schema: code.ports - a port's members, their fn types and defaults")
   schema_case("modules/ports", "{\"port\": \"Clock\", \"member\": \"now\", \"fn\": \"game_hours\", \"value\": \"fn game_hours\", \"module\": \"app\", \"at\": \"examples/modules/station/app/index.ludic:3:14\"}", "--emit-schema: code.binds - a bind's member, the function it names and where")