Add Daily briefing JSON generation

docs/cli.md

@@ -1,8 +1,8 @@
 # Weatherreporter CLI
 
-`weatherreporter` currently resolves configuration, command requests, report
-definitions, and valid periods, then returns a not-implemented error for report
-generation and scheduled runs.
+`weatherreporter generate daily` currently writes a Daily briefing JSON artifact.
+Other report generation and scheduled runs still resolve configuration, report
+definitions, and valid periods, then return a not-implemented error.
 
 ## Shortest Useful Command
 
@@ -10,8 +10,8 @@ generation and scheduled runs.
 weatherreporter generate daily --date 2026-05-29 --out ./daily.md
 ```
 
-The command parses flags, loads configuration, resolves report identity and the
-valid period, and then stops before weather data fetching or report rendering.
+The command parses flags, loads configuration, fetches weather data, builds a
+Daily briefing, and writes the JSON artifact to `--out`.
 
 ## Command Overview
 
@@ -25,9 +25,9 @@ weatherreporter run morning
 weatherreporter run evening
 ```
 
-`generate` commands resolve one report request. `run` commands resolve a
-scheduled batch request. All report and batch execution currently returns
-`not implemented` after request resolution.
+`generate daily` writes a briefing JSON artifact. Other `generate` commands
+resolve one report request and stop before report generation. `run` commands
+resolve a scheduled batch request and stop before execution.
 
 ## Flags
 
@@ -35,7 +35,7 @@ scheduled batch request. All report and batch execution currently returns
 - `--config PATH`: load configuration from `PATH` instead of `/usr/local/etc/weatherreporter/config.yml`.
 - `--units VALUE`: override configured Weather API units.
 - `--tz NAME`: override configured Weather API timezone.
-- `--out PATH`: override report output path or directory for `generate` commands.
+- `--out PATH`: output path for `generate daily`; reserved for later generated report output on other `generate` commands.
 - `--date YYYY-MM-DD`: optional date for `generate daily`; defaults to the current local date in the configured timezone.
 - `--start TIME`: required start time for `generate storm`.
 - `--end TIME`: required end time for `generate storm`.

docs/internal/briefing.md

@@ -0,0 +1,59 @@
+# Briefing Internals
+
+This document describes the implemented briefing package boundary.
+
+## Purpose
+
+`internal/briefing` builds structured report-specific briefing packages from
+forecast summaries and report metadata. The package currently implements the
+Daily briefing only.
+
+## Inputs and Outputs
+
+Inputs:
+
+- resolved report definition and valid period
+- forecast bundle
+- derived daily forecast summary
+- configured units and timezone
+
+Output:
+
+- `briefing.Package` JSON containing common metadata and Daily briefing content
+
+## Boundaries
+
+- Briefings are structured weather facts and context for later prompt input.
+- This package does not fetch weather data, compare prior snapshots, build
+  `scriptorium` data packages, or render final report prose.
+
+## Behavior
+
+- Common metadata includes schema version, RunID, report ID, variant, prompt ID,
+  generation time, units, timezone, valid period, source location, source
+  provenance, hashes, and source warnings.
+- Daily content includes bottom-line inputs, daypart summaries, relevant alerts,
+  outdoor window inputs, narrative periods, discussion context, and weather
+  story context when available.
+- Briefing JSON is written atomically by `briefing.Save`.
+
+## Failure Behavior
+
+- Daily briefing construction requires a Daily report definition and a derived
+  daily forecast summary.
+- Save failures include path and operation context.
+
+## Tests
+
+Inspect:
+
+- `internal/briefing/daily_test.go`
+- `internal/app/app_test.go`
+- `internal/cli/root_test.go`
+
+## Invariants
+
+- Weather facts come from normalized and derived source data.
+- Briefing output remains JSON-inspectable.
+- LLM prompt input packaging and `scriptorium` execution remain outside this
+  boundary.