feat(aircoding): AirCoding V2 baseline — deterministic multi-agent architecture

Forked from OpenCode v1.17.4 with multi-agent system:
- 5 agents: aircoding, scheduler, worker, architect, reviewer
- Deterministic DAG scheduling engine (coordinator_tick)
- Tool whitelists as hard enforcement
- AirCoding validation plugin
- System prompt injection for routing
- V1 requirements: C4 docs, ADR, AGENTS.md, debug-log.md
- Design documents in docs/

packages/tui/src/prompt/display.ts

@@ -0,0 +1,48 @@
+const graphemes = new Intl.Segmenter(undefined, { granularity: "grapheme" })
+
+export function promptOffsetWidth(value: string) {
+  let width = 0
+  for (const part of graphemes.segment(value)) {
+    // Textarea offsets count newlines as one position; Bun.stringWidth counts them as zero.
+    width += part.segment === "\n" ? 1 : Bun.stringWidth(part.segment)
+  }
+  return width
+}
+
+function displayOffsetIndex(value: string, offset: number) {
+  if (offset <= 0) return 0
+
+  let width = 0
+  for (const part of graphemes.segment(value)) {
+    const next = width + promptOffsetWidth(part.segment)
+    if (next > offset) return part.index
+    width = next
+  }
+
+  return value.length
+}
+
+export function displaySlice(value: string, start = 0, end = promptOffsetWidth(value)) {
+  return value.slice(displayOffsetIndex(value, start), displayOffsetIndex(value, end))
+}
+
+export function displayCharAt(value: string, offset: number) {
+  let width = 0
+  for (const part of graphemes.segment(value)) {
+    const next = width + promptOffsetWidth(part.segment)
+    if (offset === width || offset < next) return part.segment
+    width = next
+  }
+}
+
+export function mentionTriggerIndex(value: string, offset = promptOffsetWidth(value)) {
+  const text = displaySlice(value, 0, offset)
+  const index = text.lastIndexOf("@")
+  if (index === -1) return
+
+  const before = index === 0 ? undefined : text[index - 1]
+  const query = text.slice(index)
+  if ((before === undefined || /\s/.test(before)) && !/\s/.test(query)) {
+    return promptOffsetWidth(text.slice(0, index))
+  }
+}