HS-plan: cluster 32 MutationObserver blocked (env + scope)

loops/hs worktree ships without the sx-tree MCP binary built; even
after running `dune build bin/mcp_tree.exe` this iteration, tools
don't surface mid-session and the block-sx-edit hook prevents raw
`.sx` edits. The cluster scope itself spans parser/compiler/runtime
plus JS mock plus generator skip-list, so even with sx-tree loaded
it's a multi-commit job for a dedicated worktree.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plans/hs-conformance-scoreboard.md

@@ -7,7 +7,7 @@ Baseline:   1213/1496 (81.1%)
 Merged:     1277/1496 (85.4%)   delta +64
 Worktree:   all landed
 Target:     1496/1496 (100.0%)
-Remaining:  ~219 tests (clusters 17/22/29/31 blocked; 31 needs design doc)
+Remaining:  ~219 tests (clusters 17/22/29/31/32 blocked; 31/32 need dedicated sx-tree worktree)
 ```
 
 ## Cluster ledger
@@ -62,7 +62,7 @@ Remaining:  ~219 tests (clusters 17/22/29/31 blocked; 31 needs design doc)
 | # | Cluster | Status | Δ |
 |---|---------|--------|---|
 | 31 | runtime null-safety error reporting | blocked | — |
-| 32 | MutationObserver mock + `on mutation` | pending | (+10–15 est) |
+| 32 | MutationObserver mock + `on mutation` | blocked | — |
 | 33 | cookie API | pending | (+5 est) |
 | 34 | event modifier DSL | pending | (+6–8 est) |
 | 35 | namespaced `def` | pending | (+3 est) |
@@ -88,7 +88,7 @@ Defer until A–D drain. Estimated ~25 recoverable tests.
 | A      | 12   | 4       | 0       | 0       | 1       | —           | 17    |
 | B      | 6    | 0       | 0       | 0       | 1       | —           | 7     |
 | C      | 4    | 0       | 0       | 0       | 1       | —           | 5     |
-| D      | 0    | 0       | 0       | 4       | 1       | —           | 5     |
+| D      | 0    | 0       | 0       | 3       | 2       | —           | 5     |
 | E      | 0    | 0       | 0       | 0       | 0       | 5           | 5     |
 | F      | —    | —       | —       | ~10     | —       | —           | ~10   |