chore: standardize TypeScript version to 6.0.2 across workspace

- Updated pnpm-workspace.yaml to enforce TypeScript version 6.0.2.
- Replaced legacy TypeScript import with the current version in comparison tools.
- Added ignoreDeprecations setting in tsconfig.base.json to suppress deprecation warnings for baseUrl.
- Introduced TypeScript version policy documentation outlining the rationale and upgrade gate for moving to TypeScript 7.

docs/architecture/runtime.md

@@ -4,6 +4,18 @@ Build outputs should be emitted to `/dist/{profileName}` per profile to keep
 deployments predictable. Profiles are server+scenario pairs, and scenario
 selection is required because it drives unit sets and DB settings.
 
+## TypeScript Toolchain
+
+The rewrite workspace uses exactly TypeScript `6.0.2`. TypeScript 7 is not a
+supported build or validation environment until the compiler/tooling APIs used
+by this repository and the dependent toolchain are available and compatible.
+Package-local TypeScript 5 or 7 overrides are not allowed in `app/*`,
+`packages/*`, or `tools/*`. The legacy runtime under `legacy/` is maintained
+separately and is outside this rule.
+
+The rationale, scope, and TypeScript 7 upgrade gate are defined in
+[`typescript-version.md`](typescript-version.md).
+
 ## Database Schemas (Gateway vs Game)
 
 Gateway uses a shared schema (default `public`) for login/profile state, while

docs/architecture/typescript-version.md

@@ -0,0 +1,55 @@
+# TypeScript Version Policy
+
+## Decision
+
+The `core2026` rewrite workspace standardizes on exactly TypeScript `6.0.2`.
+TypeScript 7 must not be introduced into individual workspace packages while
+this policy is active.
+
+This is a temporary compatibility decision. TypeScript 7 currently does not
+provide all compiler/tooling APIs required by this repository and its dependent
+tools, which has caused typecheck, lint, and comparison-tool failures. The
+workspace will remain on TypeScript 6 until those APIs and the surrounding
+tooling support are available.
+
+## Scope
+
+This policy applies to every pnpm workspace package under:
+
+- `app/*`
+- `packages/*`
+- `tools/*`
+- the root development toolchain
+
+All direct `typescript` dependencies in that scope must use the exact version
+`6.0.2`. Do not use a caret range, package-local TypeScript 5 fallback, a
+TypeScript 7 override, or an alias to another TypeScript version. A single
+version must be resolved in `pnpm-lock.yaml`; the root `pnpm-workspace.yaml`
+override enforces the same version for transitive TypeScript peer resolution.
+
+The PHP runtime and its historical frontend under `legacy/` are not pnpm
+workspace packages and retain their existing toolchain. This exception must not
+be used by rewrite packages.
+
+TypeScript 6 reports the existing `baseUrl` configuration as deprecated. The
+shared `tsconfig.base.json` sets `ignoreDeprecations` to `6.0` so the current
+path mapping continues to work during this compatibility period. Removing or
+replacing `baseUrl` remains part of the TypeScript 7 upgrade work; packages must
+not add their own suppression values.
+
+## TypeScript 7 Upgrade Gate
+
+Moving to TypeScript 7 requires a deliberate workspace-wide change. Upgrade
+only after all of the following are true:
+
+1. The compiler/tooling APIs used by repository scripts are available.
+2. `typescript-eslint`, `vue-tsc`, `tsdown`, Vite integrations, and other direct
+   TypeScript consumers officially support the selected TypeScript 7 release.
+3. `CI=1 pnpm typecheck`, `pnpm lint`, `pnpm build`, and relevant tests pass.
+4. Legacy comparison tools, including `pnpm check:legacy:nation`, pass without
+   a fallback TypeScript installation or version alias.
+5. Every workspace manifest and `pnpm-lock.yaml` is updated together so only
+   the approved TypeScript 7 version is resolved for the rewrite workspace.
+
+Until this gate is satisfied, failures caused by running TypeScript 7 are not a
+supported baseline and must not be worked around by mixing compiler versions.

docs/testing-policy.md

@@ -47,6 +47,9 @@ information only, not evidence of correctness.
 - Validate domain constraints in the logic layer where possible; DB constraints
   act as a secondary safety net.
 - Use deterministic seeds for all gameplay-impacting RNG.
+- Run TypeScript validation with the workspace-standard TypeScript `6.0.2`.
+  TypeScript 5 or 7 results do not replace the required repository typecheck.
+  See `docs/architecture/typescript-version.md`.
 
 ## Test Layers