M1: evidence types, Source port, ScrubTitle

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/evidence/evidence.go

@@ -0,0 +1,39 @@
+// Package evidence is the activity port: a dumb active-window sensor behind a
+// Source interface, plus the value types it emits. It makes no judgment about
+// whether a window is on-task — that is the advisor's job in a later milestone.
+package evidence
+
+import (
+	"context"
+	"regexp"
+)
+
+// EvidenceHealth records whether the sensor could observe the active window.
+type EvidenceHealth struct {
+	Available bool   // true when a window was observed
+	Reason    string // empty when Available; populated when not
+}
+
+// WindowSnapshot is one observation of the active window.
+type WindowSnapshot struct {
+	Title  string // full _NET_WM_NAME (raw; used in live view + raw log)
+	Class  string // WM_CLASS
+	Health EvidenceHealth
+}
+
+// Source is the activity port. Watch runs until ctx is cancelled, invoking
+// onChange on every active-window change, and once immediately with the
+// current window.
+type Source interface {
+	Watch(ctx context.Context, onChange func(WindowSnapshot))
+}
+
+// titleNoise matches the legacy clock/ratio/percent runs that pollute bucket
+// keys (e.g. "1:23", "50.5%", "-3.0"). Ported verbatim from the Rust impl.
+var titleNoise = regexp.MustCompile(`-?\d+([:.]\d+)+%?`)
+
+// ScrubTitle removes volatile numeric runs so window titles bucket stably.
+// The raw event log keeps the unscrubbed title; only bucket keys are scrubbed.
+func ScrubTitle(title string) string {
+	return titleNoise.ReplaceAllString(title, "")
+}