introduce RuntimeBuilder to separate construction from orchestration in ior.go

RuntimeBuilder encapsulates allocation of per-trace-session components
(statsengine.Engine, streamrow.RingBuffer, Sequencer, flamegraph.LiveTrie);
buildTUIRuntime, buildTestFlamesRuntime, and buildTestLiveFlamesRuntime now
delegate construction to RuntimeBuilder.Build() and focus only on wiring.
wireRuntimeBindings is extracted to isolate the context-binding wiring step.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/internal/runtime_builder.go b/internal/runtime_builder.go
new file mode 100644
index 0000000..bc1c228
--- /dev/null
+++ b/internal/runtime_builder.go
@@ -0,0 +1,49 @@
+package internal
+
+import (
+	"ior/internal/flags"
+	"ior/internal/flamegraph"
+	"ior/internal/statsengine"
+	"ior/internal/streamrow"
+)
+
+const defaultEngineCapacity = 64
+
+// runtimeComponents holds the freshly allocated trace-session components
+// produced by RuntimeBuilder.Build. All fields are non-nil after a successful
+// build. The caller is responsible for wiring these into the runtime bindings
+// and event-loop callbacks.
+type runtimeComponents struct {
+	engine    *statsengine.Engine
+	streamBuf *streamrow.RingBuffer
+	streamSeq *streamrow.Sequencer
+	liveTrie  *flamegraph.LiveTrie
+}
+
+// RuntimeBuilder encapsulates the allocation of per-trace-session runtime
+// components. Construct one with newRuntimeBuilder, then call Build to
+// produce a fresh runtimeComponents struct ready for wiring.
+type RuntimeBuilder struct {
+	// cfg holds the configuration used to size and configure the components.
+	cfg flags.Config
+}
+
+// newRuntimeBuilder creates a RuntimeBuilder configured from cfg.
+// The builder captures cfg at construction time; later cfg changes do not affect
+// a builder already created.
+func newRuntimeBuilder(cfg flags.Config) RuntimeBuilder {
+	return RuntimeBuilder{cfg: cfg}
+}
+
+// Build allocates a fresh set of runtime components for one trace session.
+// It creates a new stats engine, stream ring buffer, sequencer, and live trie
+// each time it is called; callers must not share the returned components across
+// concurrent trace sessions.
+func (b RuntimeBuilder) Build() runtimeComponents {
+	return runtimeComponents{
+		engine:    statsengine.NewEngine(defaultEngineCapacity),
+		streamBuf: streamrow.NewRingBuffer(),
+		streamSeq: streamrow.NewSequencer(0),
+		liveTrie:  flamegraph.NewLiveTrie(b.cfg.CollapsedFields, b.cfg.CountField),
+	}
+}