feat: deterministic scheduler → real Now/Next/Later (P2 thin slice)

CommiTea now recommends its own next unit of work from the live backlog.

- @commitea/core: `schedule()` — dependency topo-sort with priority +
  estimate tie-breaks, single serial capacity, cycle detection, and
  critical-path marking; `selectFocus()` takes the top three. Pure,
  deterministic; the LLM does none of this. +11 tests (39 in core).
  Client gains `getIssueDependencies`.
- main: reconcile also fetches native issue dependencies for the open
  scope and returns edges.
- renderer: `scheduleFocus()` maps real issues+deps→Now/Next/Later;
  Focus renders scheduler output (fixture fallback when unconfigured).

v0 scope (each a later slice): single serial worker (per-person
capacity #8), point durations (Monte Carlo cone #10), estimate-only
(calibration #5). Verified: 14 e2e green (fixtures) + gated live spec —
the board shows the real 25 open + 9 closed, and Focus picks #2
ChangeSource (critical path) as Now. Screenshots confirmed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/core/src/scheduler/scheduler-v0.ts

@@ -0,0 +1,182 @@
+/**
+ * Deterministic scheduler, v0. Orders the open backlog by dependency topology,
+ * then priority, then estimate; lays it out on a single serial capacity and
+ * marks the critical path. The LLM never does this — it's plain code.
+ *
+ * v0 simplifications (each is a later slice, not a hack):
+ *  - single serial worker; per-person capacity is #8.
+ *  - point durations from estimate labels; Monte Carlo cones are #10.
+ *  - a null estimate defaults to DEFAULT_ESTIMATE_DAYS.
+ * Dependencies on out-of-scope issues (closed/done, or not passed in) are
+ * treated as satisfied and dropped — you schedule what's left to do.
+ */
+
+export const DEFAULT_ESTIMATE_DAYS = 2
+
+export interface SchedulableIssue {
+  number: number
+  title: string
+  labels: string[]
+  /** From label facts; null when unestimated. */
+  estimateDays: number | null
+  /** 1 (most urgent) … 4; null when unset. */
+  priority: number | null
+}
+
+export interface DependencyEdge {
+  issue: number
+  dependsOn: number
+}
+
+export interface ScheduledItem {
+  number: number
+  title: string
+  labels: string[]
+  /** 0-based position in the plan. */
+  order: number
+  /** Working-day offsets from now. */
+  startDay: number
+  endDay: number
+  durationDays: number
+  /** In-scope dependencies (all still open, so all still blocking). */
+  blockedBy: number[]
+  /** Issues that depend on this one. */
+  blocks: number[]
+  /** On a longest-duration dependency chain. */
+  critical: boolean
+  rationale: string
+}
+
+export interface SchedulePlan {
+  items: ScheduledItem[]
+  /** A dependency cycle (issue numbers) if one was found — the plan is then empty. */
+  cycle: number[] | null
+}
+
+function durationOf(issue: SchedulableIssue): number {
+  return issue.estimateDays ?? DEFAULT_ESTIMATE_DAYS
+}
+
+/** Best-first comparison among ready nodes: priority (1 first), then larger estimate, then number. */
+function readyRank(a: SchedulableIssue, b: SchedulableIssue): number {
+  const pa = a.priority ?? 99
+  const pb = b.priority ?? 99
+  if (pa !== pb) return pa - pb
+  const da = durationOf(a)
+  const db = durationOf(b)
+  if (da !== db) return db - da
+  return a.number - b.number
+}
+
+function rationaleFor(item: {
+  critical: boolean
+  blockedBy: number[]
+  blocks: number[]
+  priority: number | null
+}): string {
+  const blocksNote = item.blocks.length ? `unblocks ${item.blocks.map((n) => `#${n}`).join(', ')}` : ''
+  if (item.critical) return ['on the critical path', blocksNote].filter(Boolean).join(' · ')
+  if (item.blockedBy.length) return `waits on ${item.blockedBy.map((n) => `#${n}`).join(', ')}`
+  if (blocksNote) return blocksNote
+  if (item.priority != null) return `p/${item.priority} · ready`
+  return 'ready'
+}
+
+export function schedule(issues: SchedulableIssue[], edges: DependencyEdge[]): SchedulePlan {
+  const byNumber = new Map(issues.map((i) => [i.number, i]))
+
+  // keep only edges whose endpoints are both in scope
+  const scoped = edges.filter((e) => byNumber.has(e.issue) && byNumber.has(e.dependsOn))
+  const deps = new Map<number, number[]>() // issue → its dependencies
+  const dependents = new Map<number, number[]>() // issue → who depends on it
+  for (const i of issues) {
+    deps.set(i.number, [])
+    dependents.set(i.number, [])
+  }
+  for (const e of scoped) {
+    deps.get(e.issue)!.push(e.dependsOn)
+    dependents.get(e.dependsOn)!.push(e.issue)
+  }
+
+  // Kahn topo with priority tie-break
+  const indegree = new Map(issues.map((i) => [i.number, deps.get(i.number)!.length]))
+  const order: number[] = []
+  const ready = issues.filter((i) => indegree.get(i.number) === 0)
+  while (ready.length) {
+    ready.sort(readyRank)
+    const next = ready.shift()!
+    order.push(next.number)
+    for (const dep of dependents.get(next.number)!) {
+      const d = indegree.get(dep)! - 1
+      indegree.set(dep, d)
+      if (d === 0) ready.push(byNumber.get(dep)!)
+    }
+  }
+
+  if (order.length < issues.length) {
+    // cycle: report the nodes that never became ready
+    const stuck = issues.filter((i) => indegree.get(i.number)! > 0).map((i) => i.number)
+    return { items: [], cycle: stuck }
+  }
+
+  // longest-path (by duration) for critical-path marking
+  const longestThrough = new Map<number, number>() // node → longest chain duration passing through it
+  const before = new Map<number, number>() // longest duration of chain ending at node's start
+  for (const n of order) {
+    const depMax = Math.max(0, ...deps.get(n)!.map((d) => before.get(d)! + durationOf(byNumber.get(d)!)))
+    before.set(n, depMax)
+  }
+  const after = new Map<number, number>()
+  for (const n of [...order].reverse()) {
+    const depMax = Math.max(0, ...dependents.get(n)!.map((d) => after.get(d)! + durationOf(byNumber.get(d)!)))
+    after.set(n, depMax)
+  }
+  let globalMax = 0
+  for (const n of order) {
+    const total = before.get(n)! + durationOf(byNumber.get(n)!) + after.get(n)!
+    longestThrough.set(n, total)
+    globalMax = Math.max(globalMax, total)
+  }
+
+  // serial layout
+  let cursor = 0
+  const items: ScheduledItem[] = order.map((n, idx) => {
+    const issue = byNumber.get(n)!
+    const dur = durationOf(issue)
+    const start = cursor
+    cursor += dur
+    const blockedBy = deps.get(n)!
+    const blocks = dependents.get(n)!
+    const critical = globalMax > 0 && longestThrough.get(n) === globalMax
+    return {
+      number: n,
+      title: issue.title,
+      labels: issue.labels,
+      order: idx,
+      startDay: start,
+      endDay: cursor,
+      durationDays: dur,
+      blockedBy,
+      blocks,
+      critical,
+      rationale: rationaleFor({ critical, blockedBy, blocks, priority: issue.priority }),
+    }
+  })
+
+  return { items, cycle: null }
+}
+
+export interface Focus {
+  now: ScheduledItem | null
+  next: ScheduledItem | null
+  later: ScheduledItem | null
+}
+
+/** Now/Next/Later = the first three of the plan (already dependency- + priority-ordered). */
+export function selectFocus(plan: SchedulePlan): Focus {
+  return {
+    now: plan.items[0] ?? null,
+    next: plan.items[1] ?? null,
+    later: plan.items[2] ?? null,
+  }
+}