Fix documentation drift surfaced by the full-docs consistency review

docs/IMPLEMENTATION-PLAN.md

@@ -47,7 +47,7 @@ doc before implementing.
 | **M0**   | Skeleton ✅                 | Repo builds, tests run, empty shell renders                                    | —                                           |
 | **M1**   | **MVP core loop**           | Author a Vega-Lite snippet, see it render live, it persists                    | §02, §03A–C, §04, §09A                      |
 | **M1.5** | Visual design foundation ✅ | Apply the design language: tokens, IBM Plex, restyled M1 surfaces, chart theme | [arch 09](architecture/09-visual-design.md) |
-| **M2**   | Editor robustness           | Draft/Published, validation, schema autocomplete, fit modes                    | §03D–E, §04, §07(editor)                    |
+| **M2**   | Editor robustness ✅        | Draft/Published, validation, schema autocomplete, fit modes                    | §03D–E, §04, §07(editor)                    |
 | **M3**   | Datasets ✅                 | Named reusable data + reference resolution in preview                          | §05, §03F, §09B                             |
 | **M4**   | Chart Builder               | No-JSON chart composition from a dataset                                       | §06                                         |
 | **M5**   | Settings + Import/Export    | Preferences + workspace backup/transfer                                        | §07, §08, §09C                              |
@@ -149,7 +149,7 @@ and the companion `visual-specimen.html`.
   persisted via the `ui.theme` settings key (a minimal forward-compatible
   `settings-store` adapter the full M5 UserSettings store will absorb). Hydrated
   before first paint (no FOUC). Justified: the theme system was already complete,
-  so dogfooding dark mode through M2–M4 beat waiting for the Settings modal.
+  so dogfooding dark mode through M2–M4 beat waiting for the full settings UI.
 
 **Core**
 
@@ -242,7 +242,7 @@ user-verified in the running app.
 
 ---
 
-## M3 · Datasets
+## M3 · Datasets ✅ (done)
 
 **Goal:** named, reusable data that snippets reference by name; preview resolves
 the reference.
@@ -471,6 +471,19 @@ offline reload works; install as standalone; reduced-motion honored. **⏳ Still
 
 ---
 
+## Open divergences (spec ↔ code)
+
+Surfaced by the full-docs consistency review — each needs a deliberate resolution,
+not a silent drift:
+
+- **Storage-monitor scope.** Spec §02 frames the indicator as the **snippet** storage
+  budget specifically ("datasets are stored separately with far greater capacity"); the
+  shipped `readStorageEstimate` instead reports **whole-origin** usage/quota (snippets +
+  datasets + everything). Decide: scope the estimate to the snippet store, or update spec
+  §02 to the whole-origin reading. Noted at [arch 02 §6](architecture/02-persistence.md).
+
+---
+
 ## Architecture reference
 
 The **how** behind each milestone is documented self-containedly in