Settle discovery directory resolution errors

docs/roadmap/discovery.md

@@ -131,7 +131,7 @@ Resolve the user-configuration base with
 [`os.UserHomeDir`](https://pkg.go.dev/os#UserHomeDir), and the working-directory
 base with [`os.Getwd`](https://pkg.go.dev/os#Getwd). Adopt the Go helpers'
 platform-specific directory and environment behavior, including their errors;
-OD-2 determines how discovery responds to a resolution error.
+the settled OD-2 rules below govern how discovery handles resolution errors.
 
 The goal is to support familiar conventions through idiomatic Go. This feature
 does not add a separate XDG compatibility layer or XDG system preset. A selected
@@ -213,6 +213,29 @@ The exact Go names, constructors, and representation of search-wide options
 belong in the implementation plan. Keep the public surface root-owned and keep
 the single-preset case concise.
 
+### Unavailable Bases And Platform Applicability (OD-2 — Settled)
+
+Resolve directory bases only as the ordered search reaches them. Once an earlier
+candidate is selected, later searches do not resolve their bases. Static invalid
+search arguments still fail ordinary option validation before source acquisition.
+
+If a selected directory's base cannot be resolved, stop and report the error.
+A missing directory or candidate file beneath a resolved base allows the search
+to continue; a directory-resolution error does not. This distinction also applies
+to optional searches: permitting no match does not suppress errors encountered
+while searching. Preserve the agreed errors for inaccessible or unreadable
+candidates.
+
+Treat using the Unix system preset on an unsupported platform as an explicit
+configuration error when that preset is reached. Specify its supported platforms
+in the implementation plan. Do not translate the Unix preset into a different
+platform's convention. User, home, and working-directory presets use their native
+Go directory helpers.
+
+This keeps search priority predictable when directory resolution fails. Consumers
+select the presets appropriate to their application and environment; this proposal
+does not add an option to skip unavailable bases or unsupported presets.
+
 ### Placement, Provenance, And Existing Features
 
 The selected file participates as the actual file source. Preserve its physical
@@ -268,28 +291,6 @@ its in-progress changes are part of a fixed implementation baseline.
 
 ## Open Decisions
 
-### OD-2 — Unavailable Bases And Platform Applicability
-
-**Recommendation:** resolve directory bases as the ordered search reaches them.
-If a selected directory's base cannot be resolved, report an error. Treat using the
-Unix system preset on a platform where it is unsupported as an explicit
-configuration error when that preset is reached. Specify the supported platforms
-in the implementation plan. Do not silently translate the Unix preset into a
-different platform's convention. User, home, and working-directory presets use their
-platform-native bases.
-
-An unavailable base is different from a candidate file being absent. Failure to
-determine the user's configuration directory should not silently redirect loading
-to a different directory. Once an earlier candidate is selected, later searches need
-not resolve their bases. Static invalid search arguments still fail ordinary
-option validation before source acquisition.
-
-**Alternative:** treat unsupported presets or unavailable bases as empty searches
-and continue. This makes one preset composition usable across more environments,
-but can unexpectedly select a lower-priority configuration. A selectable
-skip-unavailable behavior could serve that need later; it adds a distinct policy
-from the search-wide requirement that at least one file exist.
-
 ### OD-3 — No Match, Imports, And Selected Overlays
 
 **Recommendation:** use a shared absent-main lifecycle for optional no-match and