fix(agent): the assistant reaches earlier räkenskapsår: period resolved from dates, years listed in the grounding (#2436)

Part 3 of #2185. A user with several imported years concluded the assistant
"only reads the period I am standing in". Nothing restricted it: the report
tools defaulted to the most recent fiscal period when no period_id was given
and then rejected any from_date/to_date/as_of_date outside it, and neither
the snapshot nor the chat identity block told the model which years existed
or how to address them.

- extensions/general/mcp-server/server.ts: resolveReportPeriod takes a date
  hint; without period_id, a date in the call resolves the fiscal period that
  contains it (findFiscalPeriodContaining, company-scoped), and a date no
  period covers fails with the company's span instead of the latest year's
  bounds. Income statement (from_date or to_date), balance sheet (as_of_date)
  and dimension P&L (to_date) use it. The range guard is unchanged. No schema
  change: tools/list sits at its token ceiling.
- lib/agent/fiscal-years.ts: one query and one line, "Räkenskapsår (senaste
  först): ... period_id=<uuid> (senaste|avslutat)", plus the rule on
  addressing an earlier year, shared by the single-call snapshot and the
  streaming chat's always-on identity block.
- lib/agent/intents/shared-rules.ts and TOOL_RULES: pass that year's
  period_id, one call per year, and say which räkenskapsår the answer covers.


Claude-Session: https://claude.ai/code/session_0179bdetHyofL6ATfQxB5wP5

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

lib/agent/__tests__/fiscal-years.test.ts

@@ -0,0 +1,67 @@
+import { describe, it, expect } from 'vitest'
+import type { SupabaseClient } from '@supabase/supabase-js'
+import {
+  FISCAL_YEAR_INVENTORY_CAP,
+  loadFiscalYearInventory,
+  renderFiscalYearInventory,
+} from '../fiscal-years'
+
+function supabaseReturning(result: { data?: unknown; error?: unknown } | Error): {
+  supabase: SupabaseClient
+  calls: { method: string; args: unknown[] }[]
+} {
+  const calls: { method: string; args: unknown[] }[] = []
+  const chain: Record<string, unknown> = {}
+  for (const method of ['select', 'eq', 'order', 'limit']) {
+    chain[method] = (...args: unknown[]) => {
+      calls.push({ method, args })
+      return chain
+    }
+  }
+  chain.then = (onFulfilled: (v: unknown) => unknown, onRejected?: (e: unknown) => unknown) =>
+    (result instanceof Error ? Promise.reject(result) : Promise.resolve(result)).then(
+      onFulfilled,
+      onRejected,
+    )
+  return { supabase: { from: () => chain } as unknown as SupabaseClient, calls }
+}
+
+describe('loadFiscalYearInventory', () => {
+  it('reads the company periods newest first, capped', async () => {
+    const rows = [
+      { id: 'a', name: '2026', period_start: '2026-01-01', period_end: '2026-12-31', is_closed: false },
+    ]
+    const { supabase, calls } = supabaseReturning({ data: rows, error: null })
+    expect(await loadFiscalYearInventory(supabase, 'c1')).toEqual(rows)
+    expect(calls).toContainEqual({ method: 'eq', args: ['company_id', 'c1'] })
+    expect(calls).toContainEqual({ method: 'order', args: ['period_start', { ascending: false }] })
+    expect(calls).toContainEqual({ method: 'limit', args: [FISCAL_YEAR_INVENTORY_CAP] })
+  })
+
+  it('is best-effort: a failing query yields an empty list', async () => {
+    const { supabase } = supabaseReturning(new Error('db down'))
+    expect(await loadFiscalYearInventory(supabase, 'c1')).toEqual([])
+    const nulled = supabaseReturning({ data: null, error: { message: 'x' } })
+    expect(await loadFiscalYearInventory(nulled.supabase, 'c1')).toEqual([])
+  })
+})
+
+describe('renderFiscalYearInventory', () => {
+  it('marks the newest and the closed years and carries the period_id', () => {
+    expect(
+      renderFiscalYearInventory([
+        { id: 'fp-2026', name: '2026', period_start: '2026-01-01', period_end: '2026-12-31', is_closed: false },
+        { id: 'fp-2025', name: '2025', period_start: '2025-01-01', period_end: '2025-12-31', is_closed: true },
+        { id: 'fp-2024', name: '2024', period_start: '2024-05-01', period_end: '2025-04-30', is_closed: false },
+      ]),
+    ).toBe(
+      'Räkenskapsår (senaste först): 2026-01-01..2026-12-31 period_id=fp-2026 (senaste); ' +
+        '2025-01-01..2025-12-31 period_id=fp-2025 (avslutat); ' +
+        '2024-05-01..2025-04-30 period_id=fp-2024.',
+    )
+  })
+
+  it('is null for a company without periods, so the caller drops the line', () => {
+    expect(renderFiscalYearInventory([])).toBeNull()
+  })
+})