Document profile comparison workflow

docs/policy/architecture.md

@@ -15,6 +15,11 @@ and renders repository-owned Markdown in memory. Completed Markdown is
 atomically published to an operator-owned output destination and may then be
 uploaded through Distributor.
 
+An explicit profile comparison prepares one report input once, executes the
+same exact prompt and data package across selected profiles concurrently, and
+atomically publishes one operator-owned comparison bundle. It remains local:
+it does not create application state or send a Distributor notification.
+
 The supported report products are Daily, Today, Tomorrow, and Hourly. A batch
 collects once, validates its complete candidate prompt/profile set before
 collection, then determines and validates every planned output destination
@@ -29,6 +34,8 @@ planned report succeeds.
 - `internal/config` owns defaults, loading, validation, and secret loading.
 - `internal/app` owns in-memory workflow order, partial results, atomic output
   publication, and notification coordination through project-owned contracts.
+- `internal/comparison` owns comparison identity, durable logical bundle
+  validation, safe destination recognition, and atomic bundle publication.
 - Deterministic domain packages own weather derivation, report periods, modules,
   generated-text validation, and template contexts.
 - `internal/adapters/weatherapi`, `internal/adapters/promptkit`, and
@@ -47,6 +54,9 @@ directly.
   before collection.
 - Prompt and profile validation completes before weather collection. Raw output
   is validated before template rendering.
+- Comparison validates every explicit profile before collection, prepares one
+  immutable report input, and delegates backend capacity to Promptkit rather
+  than adding an application-wide execution limit.
 - Generated text fills defined prose slots only. Deterministic facts remain
   authoritative and repository-owned templates produce all Markdown output.
 - Sensitive rendered prompts, schemas, input bodies, provider endpoints, and
@@ -64,11 +74,16 @@ directly.
   does not remove a newly published output.
 - Configuration or explicit CLI input selects that operator-owned destination;
   it does not create an application-owned state boundary.
+- Comparison bundles are flat, versioned operator outputs. Their guarded
+  replacement accepts only a recognized current bundle; cancellation and every
+  pre-publication failure preserve a prior bundle, while individual profile
+  failures can publish a complete partial bundle.
 - Distributor uploads use only the published Markdown output, never a scan of
   local files. Single notification follows publication; batch notification
   follows publication of every selected report. Batch counters describe report
   outcomes only; a failed batch notification is represented separately at the
   batch level.
+- Comparison never invokes Distributor notification.
 - Default tests are deterministic, offline, and use Promptkit/provider fakes
   rather than live provider calls. See the [testing policy](testing.md).