Add report registry and valid periods

docs/cli.md

@@ -1,7 +1,8 @@
 # Weatherreporter CLI
 
-`weatherreporter` currently resolves configuration and command requests, then
-returns a not-implemented error for report generation and scheduled runs.
+`weatherreporter` currently resolves configuration, command requests, report
+definitions, and valid periods, then returns a not-implemented error for report
+generation and scheduled runs.
 
 ## Shortest Useful Command
 
@@ -9,8 +10,8 @@ returns a not-implemented error for report generation and scheduled runs.
 weatherreporter generate daily --date 2026-05-29 --out ./daily.md
 ```
 
-The command parses flags, loads configuration, resolves the request, and then
-stops before weather data fetching or report rendering.
+The command parses flags, loads configuration, resolves report identity and the
+valid period, and then stops before weather data fetching or report rendering.
 
 ## Command Overview
 

docs/internal/report-registry.md

@@ -0,0 +1,63 @@
+# Report Registry Internals
+
+This document describes the implemented report identity and valid-period
+boundary.
+
+## Purpose
+
+`internal/report` centralizes report IDs, prompt IDs, comparison strategies,
+valid-period resolution, report metadata, and scheduled batch membership.
+
+## Inputs and Outputs
+
+Inputs:
+
+- report ID or batch name
+- generation time
+- configured timezone
+- optional Daily date override
+- optional manual storm start and end times
+
+Outputs:
+
+- `report.Resolved` values with definition metadata and half-open valid periods
+- `report.Metadata` values suitable for later persisted run metadata
+
+## Boundaries
+
+- This package defines report identity and time coverage only.
+- It does not fetch weather data, build briefings, compare snapshots, write
+  state, or call `scriptorium`.
+
+## Behavior
+
+- Daily Today covers one configured local civil day.
+- Daily Tomorrow covers the next configured local civil day.
+- 3-Day Outlook covers generation time through local midnight after the second
+  following local civil day.
+- Weekend Outlook covers Saturday 00:00 to Monday 00:00 Monday through
+  Thursday; Friday and Saturday cover the remaining weekend from Friday 18:00
+  or generation time, whichever is later.
+- Manual Storm Report uses explicit start and end times.
+- Morning batch resolves Daily Today and 3-Day Outlook, plus Weekend Outlook
+  except on Sunday.
+- Evening batch resolves Daily Tomorrow.
+
+## Failure Behavior
+
+- Unknown report and batch names return actionable errors.
+- Sunday Weekend Outlook resolution returns an error.
+- Storm windows require start and end, with end after start.
+
+## Tests
+
+Inspect:
+
+- `internal/report/period_test.go`
+- `internal/app/app_test.go`
+
+## Invariants
+
+- Report selection goes through the registry.
+- Valid periods are independent of rendered report text.
+- Prompt IDs and comparison strategies are declared with report definitions.