The Solar Accord is not a discovery. There is no physics behind its 200-day year, no astronomical event it tracks. It is a treaty.
Before the Accord, seasons lasted as long as the prevailing prayer-coalition could hold Bryn on a given trail. A strong coalition held summer for ninety days; a collapsing one might lose the sun in forty. Agricultural planning was guesswork. War disrupted harvests indirectly: attack the monasteries and Bryn drifted, and the crops failed in a different nation than the one being invaded.
The Accord arose from exhaustion. Multiple major prayer-coalitions, after generations of sun-wars, agreed to partition Bryn's annual path: an eight-quarter cycle of roughly 25 days each, four warm quarters and four cool, totaling approximately 200 days. No coalition would push Bryn beyond the agreed seasonal band. Each would contribute singers on the scheduled rotation. The calendar that emerged is called the civil year.
What it settled and what it did not
The Accord standardized the civil year. It did not change how Bryn works. Seasons remain variable in practice—a coalition that defects from the rotation, or collapses, or loses a sun-war, extends or cuts short a quarter without warning. The 200-day calendar is the plan. It is not the guarantee.
Outside the Accord's signatory regions, the civil year means nothing. Coalitions that never signed hold Bryn on their own schedules. At the margins of the signatory zone, seasons bleed unpredictably.
The sun-tax apparatus
The Accord needed enforcement. Enforcement required infrastructure. The ecclesiastical bodies that maintain the approved singing schedule also collect the sun-tax—a tithe levied against communities in Bryn's warmth-path, paid to the coalitions that maintain the rotation. The law of light, which criminalizes unauthorized prayer-coalitions, is the legal instrument the Accord produced.
The tax and the law are technically separable from the calendar. In practice they are inseparable. The Accord survives because the bodies that benefit from the tax have every reason to defend it, and because any community that refuses to pay loses its warmth-season the following quarter.