refactor(errors): return typed problems as neverthrow Results across validation, config, fold, flows, and the library

Every failure outside the sections' API-call channel is now a member of one `Problem` union (src/problem.ts, discriminated on `code`) returned as a neverthrow `Result`/`ResultAsync` instead of a thrown domain error or a `{error: string}` shape. `describeProblem` is the one renderer; the action edge (`failRun`, `run()`) renders there, so every line the action prints, every output, summary, and exit code is unchanged (the e2e corpus is green as it was).

Converted: `validateSectionShapes`, `validateSettingsDoc`, `mergeLayers` (the admission walk returns Results; the `LayerRefusal` throw and `describeRefusal` are gone, their prose lives in `describeProblem` as the `layer-*` cases under the same value-free invariant), `parseSettingsDoc`, `readSettingsFile` (now takes the file's role, which selects the advice), `readLayerFiles`, `foldLayers`, `runSingle`, `runMulti` (a `safeTry` async generator; `orTee` flushes the buffered central warnings on the fatal paths), `runMerge` (returns the finished merge; `concludeMerge` writes the summary), `parseConfig` (`safeTry`), `parseReposInput`, `parseRepoSlug`, `resolveCentralTargets`, `discoverRepos` (`ResultAsync.fromPromise`), `parseRecipient`, and the library's `validateSettings`.

`isPlainObject` moves to src/plain-data.ts so the renderer and the fold share it; `quoteList` moves to src/problem.ts. `ARTIFACT_NEEDS_UPLOADER` is gone: `requireUploader` returns the `artifact-uploader-missing` problem and `openReportChannel`'s backstop throw renders it. `architecture.yml` gains the `problem` layer (edges from engine, flows, discovery, report, library; problem reads github and plain-data).

Tests assert on `code` and the structured payload; test/problem.test.ts renders one specimen per member, typed over every code so a new member fails compilation until it has both a case and a specimen.

Author: settings-as-code-release

.github/scripts/changed-sections.ts

@@ -77,6 +77,7 @@ export const ALL_SELECTING_PREFIXES = [
   "src/plain-data.ts",
   "src/private-open.ts",
   "src/private.ts",
+  "src/problem.ts",
   "src/schema.ts",
   "src/types.ts",
   "test/e2e/",

architecture.yml

@@ -18,6 +18,7 @@ layers:
   report: [src/report/]
   schema: [src/schema.ts]
   io: [src/io.ts]
+  problem: [src/problem.ts]
   types: [src/types.ts]
   plain-data: [src/plain-data.ts]
   private: [src/private.ts, src/private-open.ts]
@@ -34,12 +35,13 @@ exclude:
 edges:
   main: [action]
   action: [library]
-  library: [discovery, engine, flows, github, io, report, schema, sections, types]
-  flows: [discovery, engine, github, io, private, report, schema]
-  engine: [discovery, github, io, plain-data, schema, sections, types]
+  library: [discovery, engine, flows, github, io, problem, report, schema, sections, types]
+  flows: [discovery, engine, github, io, plain-data, private, problem, report, schema]
+  engine: [discovery, github, io, plain-data, problem, schema, sections, types]
   sections: [discovery, engine, github, schema, types, upstream-gaps]
   github: [io, plain-data]
-  discovery: [github, private]
-  report: [discovery, engine, github, io, private, schema, sections, types]
+  discovery: [github, private, problem]
+  report: [discovery, engine, github, io, private, problem, schema, sections, types]
+  problem: [github, plain-data]
   schema: [sections, types]
   upstream-gaps: [types]

docs/reference/architecture.md

@@ -239,6 +239,7 @@ graph TD
   report["src/report/"]
   schema["src/schema.ts"]
   io["src/io.ts"]
+  problem["src/problem.ts"]
   types["src/types.ts"]
   plain_data["src/plain-data.ts"]
   private["src/private.ts<br>src/private-open.ts"]
@@ -250,6 +251,7 @@ graph TD
   library --> flows
   library --> github
   library --> io
+  library --> problem
   library --> report
   library --> schema
   library --> sections
@@ -258,13 +260,16 @@ graph TD
   flows --> engine
   flows --> github
   flows --> io
+  flows --> plain_data
   flows --> private
+  flows --> problem
   flows --> report
   flows --> schema
   engine --> discovery
   engine --> github
   engine --> io
   engine --> plain_data
+  engine --> problem
   engine --> schema
   engine --> sections
   engine --> types
@@ -278,14 +283,18 @@ graph TD
   github --> plain_data
   discovery --> github
   discovery --> private
+  discovery --> problem
   report --> discovery
   report --> engine
   report --> github
   report --> io
   report --> private
+  report --> problem
   report --> schema
   report --> sections
   report --> types
+  problem --> github
+  problem --> plain_data
   schema --> sections
   schema --> types
   upstream_gaps --> types