Merge latest origin/master into feat/tui-package

Master advanced with PR #375's documentation-only simplification RFCs while the TUI merge was validating. Incorporate that exact head as a merge commit so PR #363 retains current-base ancestry without rewriting its reviewed history; no TUI behavior or generated terminal artifact changes are involved.

docs/rfc/INDEX.md

@@ -21,6 +21,9 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | Title | First proposed |
 |---|---|
 | [Prune dead public and result surface](proposed/simplification/2026-07-04-prune-dead-core-spine-surface.md) | 2026-07-04 |
+| [Make JSON-RPC completion and transport directional](proposed/simplification/2026-07-19-make-jsonrpc-directional.md) | 2026-07-19 |
+| [Retire the standalone subagent mock package](proposed/simplification/2026-07-19-retire-subagent-mock-package.md) | 2026-07-19 |
+| [Use one surface manager per session](proposed/simplification/2026-07-19-use-one-session-surface-manager.md) | 2026-07-19 |
 
 ### Architecture
 
@@ -231,6 +234,7 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | [Prune the unimplemented subagent seam vocabulary](rejected/simplification/2026-07-04-prune-unimplemented-subagent-vocabulary.md) | 2026-07-04 |
 | [Collapse workflows to the exercised foreground core](rejected/simplification/2026-07-12-collapse-workflow-to-foreground-core.md) | 2026-07-12 |
 | [Prune unused skill registry surface](rejected/simplification/2026-07-12-prune-unused-skill-registry-surface.md) | 2026-07-12 |
+| [Fold the single compaction backend into its service package](rejected/simplification/2026-07-19-fold-compaction-package-split.md) | 2026-07-19 |
 
 ### Architecture