Add runtime session validation guard for V2 tools with explicit INVALID state handling - PR 11.219

Author: DavidQ

docs/dev/reports/PR_11_219_report.md

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+# PR_11_219 Report - V2 Session Schema Validation (Runtime Guard)
+
+## Files Changed
+- `tests/runtime/V2SessionValidation.test.mjs`
+- `docs/dev/reports/PR_11_219_report.md`
+
+## Validation Cases Tested
+Per tool (`asset-browser-v2`, `palette-manager-v2`, `svg-asset-studio-v2`, `tilemap-studio-v2`, `vector-map-editor-v2`), the runtime harness tested:
+1. valid fixture payload -> expected `VALID`
+2. malformed JSON -> expected `INVALID`
+3. missing required fields -> expected `INVALID`
+4. empty payload object -> expected `INVALID`
+
+## Validation Commands Run
+1. `node --check tests/runtime/V2SessionValidation.test.mjs`  
+Result: **PASS**
+2. `node tests/runtime/V2SessionValidation.test.mjs`  
+Result: **PASS** (writes `tmp/v2-session-validation-results.json`)
+3. `node --check tools/*-v2/index.js`  
+Result: **FAIL** on Windows/Node CLI wildcard resolution (`MODULE_NOT_FOUND` for literal `tools\\*-v2\\index.js`)
+4. Explicit equivalent per-file syntax sweep for `tools/*-v2/index.js`  
+Result: **PASS** for:
+   - `tools/asset-browser-v2/index.js`
+   - `tools/palette-manager-v2/index.js`
+   - `tools/svg-asset-studio-v2/index.js`
+   - `tools/tilemap-studio-v2/index.js`
+   - `tools/vector-map-editor-v2/index.js`
+   - `tools/workspace-v2/index.js`
+
+## Pass/Fail By Case
+All five V2 tools passed all four required cases:
+- valid fixture: **PASS**
+- malformed JSON: **PASS**
+- missing required fields: **PASS**
+- empty payload: **PASS**
+
+No tool-level failures were reported in `tmp/v2-session-validation-results.json`.
+
+## Example INVALID Messages
+- `Asset Browser V2 session data is invalid. Expected payloadJson.assetCatalog.`
+- `Palette Manager V2 session data is invalid. Expected paletteJson only.`
+- `SVG Asset Studio V2 session data is invalid. Expected payloadJson.vectorAssetDocument.`
+- `Tilemap session data is invalid. Expected payloadJson.tileMapDocument.`
+- `Vector Map Editor V2 session data is invalid. Expected payloadJson.vectorMapDocument.`
+
+## No Fallback Confirmation
+- No fallback/default/demo session payloads were introduced.
+- No hidden sample loading was introduced.
+- No alternate session source was added; validation remains explicit and deterministic.
+
+## Scope Confirmation
+- No schema files changed.
+- No samples changed.
+- No games changed.
+- No Workspace Manager v1 changes.
+- No platformShell changes.
+- No `tools/shared/*` changes.
+- No V2 tool HTML structure changes.