feat: implement global workspace, working memory and the cognitive cycle

Phase 4 (ADR-0001). internal/attention scores thought candidates as a
normalised weighted sum over ten named features with a per-term
breakdown, ranked by (score, id) so ordering is total and replayable.
internal/workspace holds the capacity-limited workspace (refresh by
subject, decayed competition, explained admit/reject outcomes) and the
decaying working memory.

internal/brain runs one runtime per active mind: debounced wake-ups from
the event bus (own output never re-triggers), a settle window so
concurrently committing events are not skipped, bounded concurrent
Observe calls with per-process isolation and timeouts, deterministic
scoring, a loop detector that suppresses recurring thoughts and raises a
metacognition warning, executive dispatch by thought kind, and one
transaction per cycle whose events are published only after commit.
Every candidate, selection, attention shift and broadcast is an event
with provenance back to the triggering observation. Operators can run a
cycle, pause, resume, reset transient state and change attention
weights live; the manager reconciles runtimes with mind status.

cognition/attend is the first process: deterministic candidates from
external events using an urgency lexicon, novelty against context and
trust-based operator priority.

internal/brain/process.go

@@ -0,0 +1,97 @@
+// Package brain runs the cognitive cycle for each mind: it gathers new events,
+// asks registered cognitive processes for thought candidates, scores them
+// deterministically, admits the winners to the global workspace, dispatches
+// them to executive handlers and records every step as events (ADR-0001).
+package brain
+
+import (
+	"context"
+	"time"
+
+	"github.com/andydixon/noema/internal/attention"
+	"github.com/andydixon/noema/internal/minds"
+	"github.com/andydixon/noema/internal/workspace"
+	"github.com/andydixon/noema/pkg/events"
+	"github.com/andydixon/noema/pkg/ids"
+)
+
+// Process is a cognitive faculty. Observe must be safe to call concurrently
+// with other processes, must respect ctx, and must not mutate the state it is
+// given; it returns candidates and lets the cycle decide.
+type Process interface {
+	Name() string
+	Observe(ctx context.Context, s *State) ([]Candidate, error)
+}
+
+// Candidate is a proposed thought.
+type Candidate struct {
+	Kind         string               // attend | hypothesis | question | respond | goal | retrieve | reflect | note | action
+	Subject      string               // stable key for refresh and loop detection (entity, event id, proposition hash)
+	Summary      string               // one line, human readable
+	Content      map[string]any       // structured detail for handlers and the UI
+	Features     attention.Features   // scoring inputs
+	Confidence   float64              // epistemic confidence of the candidate itself
+	Evidence     []events.EvidenceRef // what it rests on
+	SourceEvents []ids.ID             // events that triggered it (first becomes causation)
+	// filled by the cycle
+	ID      ids.ID
+	Process string
+}
+
+// Mode is the coarse cognitive mode.
+type Mode string
+
+// Modes. Later phases add reflecting, consolidating and dreaming.
+const (
+	ModeAwake   Mode = "awake"
+	ModeFocused Mode = "focused"
+	ModeIdle    Mode = "idle"
+	ModePaused  Mode = "paused"
+)
+
+// State is what processes see: a read-only view of the mind plus service
+// handles. Nil services mean the capability is not available yet.
+type State struct {
+	Mind      minds.Mind
+	SelfModel minds.SelfModel
+	Mode      Mode
+	Cycle     int64
+	CycleID   ids.ID
+	Now       time.Time
+	NewEvents []events.Event  // since the last cycle, ascending
+	Workspace workspace.State // snapshot before this cycle
+	Services  Services
+}
+
+// Services are read handles processes may use. Extended per phase.
+type Services struct {
+	Events EventReader
+}
+
+// EventReader is the subset of the event store processes may call.
+type EventReader interface {
+	Get(ctx context.Context, id ids.ID) (events.Event, error)
+}
+
+// Handler executes an admitted thought of a given kind. Handlers run
+// sequentially after admission, may write to stores and emit events, and
+// receive the cycle's emitter so provenance links are consistent.
+type Handler func(ctx context.Context, c *Cycle, t workspace.Thought) error
+
+// Registry holds processes and handlers. It is immutable after construction.
+type Registry struct {
+	processes []Process
+	handlers  map[string]Handler
+}
+
+// NewRegistry builds a registry.
+func NewRegistry() *Registry { return &Registry{handlers: map[string]Handler{}} }
+
+// AddProcess registers a process.
+func (r *Registry) AddProcess(p Process) *Registry { r.processes = append(r.processes, p); return r }
+
+// Handle registers the handler for a thought kind.
+func (r *Registry) Handle(kind string, h Handler) *Registry { r.handlers[kind] = h; return r }
+
+// Processes returns the registered processes.
+func (r *Registry) Processes() []Process { return r.processes }