diff --git a/.claude/rules/coding-style.md b/.claude/rules/coding-style.md
index 9852d5876..82d7e65b6 100644
--- a/.claude/rules/coding-style.md
+++ b/.claude/rules/coding-style.md
@@ -75,7 +75,7 @@ Shared helper functions (used by two or more exports) should be grouped at the e
 
 Write all project documentation (plans, dev-notes, guides, refactor notes) in Japanese. Write all source code comments, TSDoc, commit messages, and test titles in English. This keeps documentation readable for the team while keeping code comments universally accessible and searchable.
 
-**Exception**: The `## CodeRabbit Findings` section in `refactor.md` must quote findings verbatim in their original language (English). Do not translate CodeRabbit output.
+**Exception**: The `## CodeRabbit Findings` section in `plan.md` must quote findings verbatim in their original language (English). Do not translate CodeRabbit output.
 
 ### TSDoc
 
@@ -106,23 +106,6 @@ Examples:
 - Stores usage → `https://svelte.dev/docs/svelte/stores`
 - Runes overview → `https://svelte.dev/docs/svelte/what-are-runes`
 
-## SvelteKit Patterns
-
-### Routes vs API Endpoints
-
-- Page routes (`+page.server.ts`): use `redirect()` to navigate
-- API routes (`+server.ts`): use `error()` — throwing `redirect()` returns a 3xx response; `fetch` follows it by default and receives the HTML page at the redirect target instead of a JSON error
-
-### Dual-Enforcement Constraints
-
-When the same constraint is enforced in two layers (e.g. Zod validation + SQL `CHECK`), add an inline comment stating each layer's role and the obligation to keep them in sync:
-
-```typescript
-// XOR constraint: dual enforcement via Zod (early validation) and a CHECK in migration.sql (last line of defense).
-// Prisma lacks @@check, so the SQL constraint is maintained manually. Keep both in sync.
-.refine(...)
-```
-
 ## Security
 
 ### Server-side Logging
@@ -139,30 +122,6 @@ console.log('Workbook created successfully');
 
 Prefer placing the single authoritative log in the service layer; remove duplicate logs in route handlers that cover the same event.
 
-## Svelte Patterns
-
-### Async Rollback: Capture State Before `await`
-
-Capture `$state` values before the first `await` for safe rollback. A concurrent update can overwrite the variable while awaiting:
-
-```typescript
-const previous = items; // capture before await
-try {
-  await saveToServer(items);
-} catch {
-  items = previous;
-}
-```
-
-### Optimistic Updates
-
-Derive computed fields (flags, labels, etc.) from the canonical data source — don't
-re-implement the derivation inline. Divergence causes a "works after reload" bug where
-the server state is correct but the client-side update is wrong.
-
-**Diagnostic**: "Not reflected live, but fixed after reload" → suspect the optimistic
-update payload, not the reactivity system.
-
 ## Code Review
 
 ### CodeRabbit Review: Severity Triage
@@ -171,7 +130,7 @@ Run `coderabbit review --plain` once after all phases are complete (not on every
 
 **Triage by severity:**
 
-- **critical / high / potential_issue (medium)**: Write all findings verbatim to a `## CodeRabbit Findings` section in `refactor.md`. The user decides which to fix before opening the PR. Do not fix any of these findings unilaterally.
+- **critical / high / potential_issue (medium)**: Write all findings verbatim to a `## CodeRabbit Findings` section in `plan.md`. The user decides which to fix before opening the PR. Do not fix any of these findings unilaterally.
 - **nitpick / info**: Defer to PR CI — CodeRabbit will re-comment on the open PR.
 
-Writing medium-and-above findings to `refactor.md` serves a dual purpose: it gives the user full visibility for a fix/defer decision, and it builds the implementer's understanding of recurring quality issues.
+Writing medium-and-above findings to `plan.md` serves a dual purpose: it gives the user full visibility for a fix/defer decision, and it builds the implementer's understanding of recurring quality issues.
diff --git a/.claude/rules/prisma-db.md b/.claude/rules/prisma-db.md
index 0ebb40448..dc6228746 100644
--- a/.claude/rules/prisma-db.md
+++ b/.claude/rules/prisma-db.md
@@ -83,6 +83,16 @@ automatically excluded. This is not an IS NOT NULL check; the mechanism is the J
 When documenting this behavior, write "excluded by INNER JOIN" rather than
 "implicitly includes IS NOT NULL".
 
+## Dual-Enforcement Constraints
+
+When the same constraint is enforced in both Zod (early validation) and SQL `CHECK` (last line of defense), add an inline comment stating each layer's role and the obligation to keep them in sync:
+
+```typescript
+// XOR constraint: dual enforcement via Zod (early validation) and a CHECK in migration.sql (last line of defense).
+// Prisma lacks @@check, so the SQL constraint is maintained manually. Keep both in sync.
+.refine(...)
+```
+
 ## Validate Constraints
 
 Prisma does not support `@@check`. To add one:
diff --git a/.claude/rules/svelte-components.md b/.claude/rules/svelte-components.md
index 9739f468b..028cf1fc8 100644
--- a/.claude/rules/svelte-components.md
+++ b/.claude/rules/svelte-components.md
@@ -37,48 +37,6 @@ Import from `flowbite-svelte`. Use Tailwind CSS v4 utility classes. Dark mode: `
 
 When copying button styles from a reference component, always check all three axes: `color`, `size`, and `class`. Omitting `color` applies Flowbite's default (filled blue).
 
-## `let`/`const` — Reactive Data Requires `$derived`
-
-Plain `let` or `const` in Svelte 5 component `<script>` executes once at component creation. Values derived from props or server data must use `$derived()`:
-
-```md
-// Bad: captures only the initial value — won't update when data reloads
-let user = data.loggedInUser; const categories = availableCategories.filter(...);
-
-// Good
-let user = $derived(data.loggedInUser); let categories = $derived(availableCategories.filter(...));
-```
-
-`pnpm check` warns: "This reference only captures the initial value."
-
-## `$state()` Initialization with `$props()`
-
-Referencing `$props()` inside `$state()` initializer triggers "This reference only captures the initial value". Wrap with `untrack` if intentional:
-
-```svelte
-let count = $state(untrack(() => initialCount)); // intentional: prop is initial seed only
-```
-
-## `$effect` — Store Reading
-
-Inside `$effect`, use `$store` syntax, not `get(store)`. `get()` bypasses the signal graph — the effect will not re-run when the store updates:
-
-```svelte
-// Bad: get() takes a snapshot; effect won't react to store changes
-$effect(() => {
-  const grade = get(myStore).get(key) ?? fallback;
-});
-
-// Good: $store subscribes and re-runs the effect on updates
-$effect(() => {
-  const grade = $myStore.get(key) ?? fallback;
-});
-```
-
-## `$derived` — No Arrow Wrapper
-
-Use `$derived(expr)`, not `$derived(() => expr)`. The arrow form makes the derived value a _function_, not a reactive value — dependencies may not be tracked and the template call site is confusing.
-
 ## `{@const}` Placement
 
 `{@const}` must be an **immediate child** of a block statement (`{#if}`, `{#each}`, `{:else}`, `{#snippet}`, etc.). Placing it inside an HTML element is a compile error:
@@ -127,7 +85,12 @@ replaceState(buildUpdatedUrl($page.url, activeTab), {});
 
 ## `{#each}` — Keys and Empty-list Fallback
 
-Always provide a key expression when the list or its items may change dynamically.
+Always provide a key expression on every `{#each}` block. Prefer a unique field (`id`, `name`, etc.); fall back to the index `(i)` only when no unique field exists.
+
+```svelte
+{#each items as item (item.id)}   <!-- unique field preferred -->
+{#each labels as label (i)}        <!-- index fallback -->
+```
 
 **Filter before `{#each}`, not inside it.** When visibility depends on a predicate (e.g. `canRead`), derive a filtered list once and iterate over it — never repeat the predicate inside a `{#if}` within the loop. This avoids computing the condition twice and keeps the template clean:
 
diff --git a/.claude/rules/svelte-runes.md b/.claude/rules/svelte-runes.md
new file mode 100644
index 000000000..6d339bbb1
--- /dev/null
+++ b/.claude/rules/svelte-runes.md
@@ -0,0 +1,99 @@
+---
+description: Svelte 5 Runes and reactivity rules
+paths:
+  - 'src/**/*.svelte'
+  - 'src/lib/stores/**/*.svelte.ts'
+  - 'src/features/**/stores/**'
+---
+
+# Svelte Runes & Reactivity
+
+## `SvelteMap<K, V>` — Always Provide Type Parameters
+
+`SvelteMap` without type parameters makes `.get()` return `unknown`. Always declare with explicit types:
+
+```typescript
+// Bad: .get() returns unknown — causes type errors at call sites
+const map = new SvelteMap();
+
+// Good: .get() returns TaskResults | undefined
+const map = new SvelteMap<TaskGrade, TaskResults>();
+```
+
+`$state()` wrapping is unnecessary — `SvelteMap` is already reactive (`svelte/no-unnecessary-state-wrap`). Reset with `.clear()` rather than reassigning.
+
+`svelte/prefer-svelte-reactivity` targets only `$state` contexts. Inside `$derived`, a plain `new Map()` is sufficient — the reactive dependency is tracked at the `$derived` level, not via `SvelteMap` mutation signals. Do not introduce `SvelteMap` inside `$derived` solely to satisfy this rule.
+
+## `let`/`const` — Reactive Data Requires `$derived`
+
+Plain `let` or `const` in Svelte 5 component `<script>` executes once at component creation. Values derived from props or server data must use `$derived()`:
+
+```typescript
+// Bad: captures only the initial value — won't update when data reloads
+let user = data.loggedInUser;
+
+// Good
+let user = $derived(data.loggedInUser);
+```
+
+`pnpm check` warns: "This reference only captures the initial value."
+
+## `$state()` Initialization with `$props()`
+
+Referencing `$props()` inside `$state()` initializer triggers "This reference only captures the initial value". Wrap with `untrack` if intentional:
+
+```svelte
+let count = $state(untrack(() => initialCount)); // intentional: prop is initial seed only
+```
+
+## `$effect` — Store Reading
+
+Inside `$effect`, use `$store` syntax, not `get(store)`. `get()` bypasses the signal graph — the effect will not re-run when the store updates:
+
+```svelte
+// Bad: get() takes a snapshot; effect won't react to store changes
+$effect(() => {
+  const grade = get(myStore).get(key) ?? fallback;
+});
+
+// Good: $store subscribes and re-runs the effect on updates
+$effect(() => {
+  const grade = $myStore.get(key) ?? fallback;
+});
+```
+
+## `$derived` — Prefer Over `$state` + `$effect`
+
+When a value is purely computed from other state, use `$derived` instead of initializing with `$state` and updating in `$effect`:
+
+```typescript
+// Bad: unnecessary mutation via $effect
+let items = $state<Item[]>([]);
+$effect(() => {
+  items = source.filter(isActive);
+});
+
+// Good: $derived — reactive, no mutation needed
+let items = $derived(source.filter(isActive));
+```
+
+**Do not pass an arrow function to `$derived`**: `$derived(() => fn(x))` stores the arrow function itself as the derived value — `fn` is never called and `x` is not tracked as a dependency. Use `$derived(fn(x))` for single expressions, or `$derived.by(() => { ... })` when multiple statements are needed. `$derived(expr)` is equivalent to `$derived.by(() => expr)` — the `.by` variant exists solely to allow a multi-statement function body.
+
+## Async Rollback: Capture State Before `await`
+
+Capture `$state` values before the first `await` for safe rollback. A concurrent update can overwrite the variable while awaiting:
+
+```typescript
+const previous = items; // capture before await
+try {
+  await saveToServer(items);
+} catch {
+  items = previous;
+}
+```
+
+## Optimistic Updates
+
+Derive computed fields (flags, labels, etc.) from the canonical data source — don't re-implement the derivation inline. Divergence causes a "works after reload" bug where the server state is correct but the client-side update is wrong.
+
+**Diagnostic**: "Not reflected live, but fixed after reload" → suspect the optimistic update payload, not the reactivity system.
diff --git a/.claude/rules/sveltekit.md b/.claude/rules/sveltekit.md
new file mode 100644
index 000000000..8d304d2a5
--- /dev/null
+++ b/.claude/rules/sveltekit.md
@@ -0,0 +1,41 @@
+---
+description: SvelteKit routing and navigation patterns
+paths:
+  - 'src/routes/**'
+  - 'src/**/*.svelte'
+---
+
+# SvelteKit Patterns
+
+## Routes vs API Endpoints
+
+- Page routes (`+page.server.ts`): use `redirect()` to navigate
+- API routes (`+server.ts`): use `error()` — throwing `redirect()` returns a 3xx response; `fetch` follows it by default and receives the HTML page at the redirect target instead of a JSON error
+
+## Internal Navigation: `resolve()` Wrapping
+
+`svelte/no-navigation-without-resolve` requires all internal navigation to use `resolve()` from `$app/paths`. Two patterns apply:
+
+**Parameterized routes** — type-safe, preferred:
+
+```typescript
+import { resolve } from '$app/paths';
+resolve('/workbooks/[slug]', { slug: workbook.slug });
+```
+
+**Static routes and computed string paths** — TypeScript declaration merging causes `ReturnType<AppTypes['RouteId']>` to resolve as `string` (the base overload in `@sveltejs/kit/types/index.d.ts` wins), making all routes require 2 arguments. Suppress with a description, and pre-compute in `<script>` when used in templates (where `@ts-expect-error` cannot be placed inline). A wrapper function does not help — the ESLint rule may not recognize `resolve()` calls inside wrappers.
+
+```typescript
+// @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+const homeHref = resolve('/');
+```
+
+**External links** — add `rel="noreferrer external"` instead of wrapping with `resolve()`.
+
+**Do not pass query strings to `resolve()`** — `resolve()` accepts route patterns only (e.g. `'/workbooks'`). A path like `'/workbooks?tab=foo'` is not a valid route pattern and causes a type error. Split path and search before passing: `resolve(url.pathname) + url.search`.
+
+**Do not apply `resolve()` to URLs derived from `$page.url`** — `$page.url` is the actual browser URL with the base path already applied. Wrapping a value derived from it with `resolve()` double-applies the base path. Pass the `URL` object directly to `replaceState` or extract `.pathname + .search` without `resolve()`.
+
+## Page Component Props
+
+SvelteKit page components (`+page.svelte`) accept only `data` and `form` as props (`svelte/valid-prop-names-in-kit-pages`). Commented-out features that reference other props are not "dead code" — remove only the violating prop declaration, preserve the feature code.
diff --git a/AGENTS.md b/AGENTS.md
index 7f234e509..87cf970db 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -16,7 +16,7 @@ Always prefer simplicity over pathological correctness. YAGNI, KISS, DRY. No bac
 2. Before writing a new function, search `src/lib/utils/`, `src/lib/services/`, `src/features/*/utils/` and `src/features/*/services/` for existing implementations; extract shared logic there when it appears in 2+ places
 3. Write tests first, then implement production code, then verify with `pnpm test:unit`
 4. Review critically after implementing: flag YAGNI violations, over-abstraction, missing tests
-5. After all phases complete (feature and refactor branches only — not hotfixes or dependency bumps): run a mandatory refactor cycle. Produce `refactor.md` in the same directory as the plan, documenting: design decisions made, changes explicitly rejected and why, remaining tasks, and per-phase lessons. Transfer all lessons to `plan.md`, then discard `phase-N.md` files. Run `coderabbit review --plain`; write all findings of `critical` / `high` / `potential_issue` (medium) to a `## CodeRabbit Findings` section in `refactor.md`. The user decides which to fix before opening a PR; do not fix any finding unilaterally. `nitpick` findings defer to PR CI.
+5. After all phases complete (feature and refactor branches only — not hotfixes or dependency bumps): run a mandatory refactor cycle. Write to `plan.md`: novel lessons (implementation blockers, non-obvious patterns not already in rules) and remaining tasks. Discard `phase-N.md` files. Run `coderabbit review --plain`; write all findings of `critical` / `high` / `potential_issue` (medium) to a `## CodeRabbit Findings` section in `plan.md`. The user decides which to fix before opening a PR; do not fix any finding unilaterally. `nitpick` findings defer to PR CI.
 6. Run `/session-close` at the end of each session: updates plan checklist, proposes rule/skill additions, checks for bloat, and detects repeated instructions
 
 ## Tech Stack
diff --git a/docs/dev-notes/2026-03-22/eslint-plugin-svelte-update/plan.md b/docs/dev-notes/2026-03-22/eslint-plugin-svelte-update/plan.md
new file mode 100644
index 000000000..9dae162a4
--- /dev/null
+++ b/docs/dev-notes/2026-03-22/eslint-plugin-svelte-update/plan.md
@@ -0,0 +1,83 @@
+# eslint-plugin-svelte v3.10.1 → v3.16.0 アップデート対応
+
+## 概要
+
+PR #3297（定期依存アップデート）で eslint-plugin-svelte を v3.10.1 から v3.16.0 へ更新したことにより、CI の lint チェックが失敗している。本計画では新規追加・severity 変更されたルールへの対応を行い、CI を通過させる。
+
+エラー（CI blocking）を優先して修正し、可能な限り warning も解消する。
+
+## 変更内容と背景
+
+v3.10.1 → v3.16.0 で追加・変更されたルール:
+
+| ルール                                 | 旧        | 新    | 内容                                          |
+| -------------------------------------- | --------- | ----- | --------------------------------------------- |
+| `svelte/no-navigation-without-resolve` | なし      | error | 内部ナビゲーションに `resolve()` の使用を強制 |
+| `svelte/prefer-svelte-reactivity`      | なし      | error | `Map`/`Set` 等の代わりに `SvelteMap` 等を要求 |
+| `svelte/require-each-key`              | なし/warn | warn  | `{#each}` にキーを要求                        |
+| `svelte/prefer-writable-derived`       | なし      | warn  | `$state` + `$effect` → `$derived` を推奨      |
+
+**`resolve()` の実体:** `import { resolve } from '$app/paths'`
+SvelteKit 2.55.0 で実装済み。`resolveRoute` は deprecated となり `resolve` に統一された。
+ベースパスをパスに付与する純粋な関数。除外条件: 絶対URL、`rel="external"` 属性、空文字列、hash fragment。
+
+**導入背景:** SvelteKit はルートパス以外（例: `example.com/my-app/`）へのデプロイをサポートするが、`<a href="/foo">` や `goto('/foo')` のようにパスをハードコードすると base path が加味されずナビゲーションが壊れる。`resolve()` は base path を実行時に付与する純粋関数としてこれを解決する。JS のモジュール解決（webpack alias 等）と概念は近いが、モジュール解決がビルド時に静的確定するのに対し、`resolve()` は base path がデプロイ設定に依存して実行時まで確定しないため、明示的な関数呼び出しとして設計されている。`eslint-plugin-svelte` v3.12.0 でルール化された。
+
+**メリット:** base path が変わってもコードの修正不要 / `resolve('/blog/[slug]', { slug })` 形式でルートパラメータをコンパイル時に型検査できる / 全内部ナビゲーションが一貫した経路を通るため挙動が予測しやすい。
+
+**デメリット:** 全コンポーネントに import が必要でボイラープレートが増加 / base path を使わないプロジェクトでは恩恵が見えにくく冗長に感じる / 既存コードへの適用コストが高い（本件がまさにそれ）。
+
+> 出典: [$app/paths — SvelteKit 公式ドキュメント](https://svelte.dev/docs/kit/$app-paths) / [no-navigation-without-resolve — eslint-plugin-svelte](https://github.com/sveltejs/eslint-plugin-svelte/blob/main/docs/rules/no-navigation-without-resolve.md)
+
+**`SvelteMap` の実体:** `import { SvelteMap } from 'svelte/reactivity'` — Svelte 5 でリアクティブな `Map` として提供。`.set()` / `.clear()` 等の変更を `$derived` / `$effect` に伝播する。`$state` ラッパーは不要。
+
+**導入背景:** Svelte 5 のリアクティビティはプロキシベースだが、`Map` 等のネイティブ組み込み型はエンジン内部実装のためプロキシでトラップできない（`$state(new Map())` では `.set()` が伝播しない）。`SvelteMap` はメソッドをオーバーライドしてシグナルと連携することで解決。本プロジェクトは v4 から v5 へ移行した経緯があり、`writable + subscribe` を機械的に置き換えた `$state + $effect` が残存していた。今回のルール追加はその技術的負債を検出したもの。
+
+## 設計方針
+
+- **機械的置き換えを基本とする**: ルールの意図に従い、最小限の変更で修正する
+- **外部リンクは `rel="external"` で明示**: `resolve()` で外部URLをラップしない。`rel` 属性に `external` を追加することで rule を満足させる
+- **`resolve()` は内部パスのみに適用**: 動的URLの場合は変数の内容（相対パスか絶対URLか）を確認してから適用
+- **警告は全件修正を目指す**: `valid-prop-names-in-kit-pages` のみコード調査が必要なため最後に対処
+
+## 却下した代替案
+
+| 案                                                   | 却下理由                                                                       |
+| ---------------------------------------------------- | ------------------------------------------------------------------------------ |
+| `no-navigation-without-resolve` をルール設定で無効化 | ルールの意図（base path 対応）は正当であり、将来のデプロイ設定変更に備えるべき |
+| `// eslint-disable-next-line` で個別無効化           | 件数が多く、保守性が下がる。真に必要な箇所（外部リンク等）に限定すべき         |
+| `SvelteMap` を `Map` の型エイリアスで代替            | ルールは型ではなくコンストラクタ呼び出しを検出するため回避不可                 |
+| PR を revert して別途対応                            | アップデート内容自体は問題なく、lint 修正のみで対応可能                        |
+
+実装フェーズ完了。`pnpm lint` 0 errors・0 warnings、`pnpm check` 既存の 2 件のみ、`pnpm test:unit` 45 ファイル 1954 件全パス。
+
+## 残課題
+
+**`users/edit/+page.svelte` — AtCoder 認証機能の再公開**
+
+コメントアウト済みの AtCoder ID 認証・バリデーションフォームは未公開状態のまま保持。`status` プロップは `valid-prop-names-in-kit-pages` 制約のため削除済みのため、再公開時は Props 設計（`data` prop への一本化等）を合わせて再検討すること。
+
+## (対応済み) PR #3298 の CodeRabbit レビュー
+
+### 修正した項目と判断
+
+| ファイル                        | 変更内容                                                                    | 判断軸                                                                                                                                                                             |
+| ------------------------------- | --------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `TaskTable.svelte`              | `$derived(() => fn)` → `$derived(fn)` + 呼び出し側 `()` 除去                | `$derived` に arrow function を渡すと関数オブジェクトを値として保持するバグ。→ rules 参照                                                                                          |
+| `account_transfer/+page.svelte` | `'account_transfer'` → `'?/account_transfer'`                               | SvelteKit named action は `?/` 必須。なければ URL 文字列として扱われフォームが動かない                                                                                             |
+| `workbooks/+page.svelte`        | `resolve(saved)` → `resolve(savedUrl.pathname) + savedUrl.search`           | `resolve()` は route pattern のみ受け付ける。query string を含む文字列は型エラー・意味的に不正。→ rules 参照                                                                       |
+| `UpdatingDropdown.svelte`       | `/signup`・`/login` href を `resolve()` でラップ                            | `no-navigation-without-resolve` ルール準拠。現状 no-op だが base path 設定時に必要                                                                                                 |
+| `KanbanBoard.svelte`            | `replaceState(resolve(...))` → `replaceState(updatedUrl)`                   | `$page.url` 由来の URL は base path 込み。`resolve()` を適用すると二重適用になる。→ rules 参照                                                                                     |
+| `AuthForm.svelte`               | `alternativePageLink: string` → `'/login' \| '/signup'`                     | 型を絞ることで `as` キャストを除去し exhaustive check を有効化                                                                                                                     |
+| `TaskGradeList.svelte`          | `run()` (svelte/legacy) → `$derived(new Map(...))`                          | `run()` は Svelte 4→5 移行。単純な変換なので `$derived` で置き換え可能                                                                                                             |
+| `TaskTable.svelte`              | `prepareContestTablesMap` 内 `new SvelteMap()` → `new Map()`                | `svelte/prefer-svelte-reactivity` は `$derived` 内の `new Map()` を対象外と確認。戻り型 `Map` と実体が一致。`SvelteMap` import は別箇所（`taskResultsMap` reduce）で必要なため維持 |
+| `account_transfer/+page.svelte` | `action` 属性と `ACCOUNT_TRANSFER_ACTION` 定数を削除（default action 使用） | PR #3298 で named action が `default:` に変更されたことによる 404 の修正。action 属性を外すのが最小変更                                                                            |
+
+### 採用しなかった指摘
+
+| 指摘                                                                     | 不採用理由                                                                                                                                 |
+| ------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------ |
+| `TagForm.svelte`: `resolve('/(admin)/tags')` → `resolve('/tags')` に変更 | `/(admin)/tags` が正しいルートID。`/tags` は別ルートになる                                                                                 |
+| `users/[username]/+page.svelte`: `resolve(PROBLEMS_PAGE)` 除去           | `<a href>` への静的パスは base path 設定時に `resolve()` が必要。除去すると将来壊れる                                                      |
+| `UpdatingDropdown.svelte`: `#each` キーを `innerId` に                   | `submission_statuses` はハードコード定数。`innerName` は一意・安定。DB 化 TODO があるが発生時に対処すれば十分（YAGNI）                     |
+| `TaskGradeList.svelte`: `!` → `?? []`                                    | Map は `taskGradeValues.map()` で全グレードを網羅初期化しており `!` は安全。`?? []` は「undefined の可能性あり」という誤ったシグナルになる |
diff --git a/src/features/tasks/components/contest-table/TaskTable.svelte b/src/features/tasks/components/contest-table/TaskTable.svelte
index f88932772..fd4d6b1d2 100644
--- a/src/features/tasks/components/contest-table/TaskTable.svelte
+++ b/src/features/tasks/components/contest-table/TaskTable.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { SvelteMap } from 'svelte/reactivity';
+
   import {
     Heading,
     Button,
@@ -9,10 +11,12 @@
     TableHead,
     TableHeadCell,
   } from 'flowbite-svelte';
+
   import type { TaskResults, TaskResult } from '$lib/types/task';
   import type {
     ContestTableProvider,
     ContestTableDisplayConfig,
+    ContestTableMetaData,
   } from '$features/tasks/types/contest-table/contest_table_provider';
   import type { ContestTaskPairKey } from '$lib/types/contest_task_pair';
 
@@ -55,11 +59,11 @@
     innerTaskTable: Record<string, Record<string, TaskResult>>;
     headerIds: Array<string>;
     contestIds: Array<string>;
-    metadata: any;
+    metadata: ContestTableMetaData;
     displayConfig: ContestTableDisplayConfig;
   }
 
-  let contestTableMaps = $derived(() => prepareContestTablesMap(providers));
+  let contestTableMaps = $derived(prepareContestTablesMap(providers));
 
   function prepareContestTablesMap(providers: ContestTableProvider[]): Map<string, ProviderData> {
     const map = new Map<string, ProviderData>();
@@ -94,7 +98,7 @@
   }
 
   function getTaskTable(abbreviationName: string) {
-    return contestTableMaps().get(abbreviationName);
+    return contestTableMaps.get(abbreviationName);
   }
 
   function getContestRoundLabel(provider: ContestTableProvider, contestId: string): string {
@@ -142,7 +146,7 @@
 
   // Update task results dynamically.
   // Computational complexity of preparation table: O(N), where N is the number of task results.
-  let taskResultsMap = $derived(() => {
+  let taskResultsMap = $derived.by(() => {
     return taskResults.reduce(
       (map: Map<ContestTaskPairKey, TaskResult>, taskResult: TaskResult) => {
         const key = createContestTaskPairKey(taskResult.contest_id, taskResult.task_id);
@@ -153,11 +157,11 @@
 
         return map;
       },
-      new Map<ContestTaskPairKey, TaskResult>(),
+      new SvelteMap<ContestTaskPairKey, TaskResult>(),
     );
   });
 
-  let taskIndicesMap = $derived(() => {
+  let taskIndicesMap = $derived.by(() => {
     const indices = new Map<ContestTaskPairKey, number>();
 
     taskResults.forEach((task, index) => {
@@ -170,13 +174,12 @@
 
   function handleUpdateTaskResult(updatedTask: TaskResult): void {
     const key = createContestTaskPairKey(updatedTask.contest_id, updatedTask.task_id);
-    const map = taskResultsMap();
 
-    if (map.has(key)) {
-      map.set(key, updatedTask);
+    if (taskResultsMap.has(key)) {
+      taskResultsMap.set(key, updatedTask);
     }
 
-    const index = taskIndicesMap().get(key);
+    const index = taskIndicesMap.get(key);
 
     if (index !== undefined) {
       const newTaskResults = [...taskResults];
@@ -190,7 +193,7 @@
 <!-- https://flowbite-svelte.com/docs/components/buttons -->
 <div class="flex justify-center md:justify-start m-4">
   <div class="flex flex-wrap justify-start gap-1 shadow-none">
-    {#each Object.entries(contestTableProviderGroups) as [type, config]}
+    {#each Object.entries(contestTableProviderGroups) as [type, config] (type)}
       <Button
         onclick={() => updateActiveContestType(type as ContestTableProviderGroups)}
         color="alternative"
diff --git a/src/features/workbooks/components/detail/WorkBookTasksTable.svelte b/src/features/workbooks/components/detail/WorkBookTasksTable.svelte
index 62e5bddf5..1e2d32bf0 100644
--- a/src/features/workbooks/components/detail/WorkBookTasksTable.svelte
+++ b/src/features/workbooks/components/detail/WorkBookTasksTable.svelte
@@ -166,7 +166,7 @@
       </TableHead>
 
       <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-        {#each workBookTasksForTable as task, index}
+        {#each workBookTasksForTable as task, index (task.taskId)}
           <TableBodyRow>
             <!-- ID -->
             <TableBodyCell class="xs:text-lg text-gray-700 dark:text-gray-300 truncate pl-6 pr-3">
diff --git a/src/features/workbooks/components/list/TitleTableBodyCell.svelte b/src/features/workbooks/components/list/TitleTableBodyCell.svelte
index 602cb75ea..f2a747913 100644
--- a/src/features/workbooks/components/list/TitleTableBodyCell.svelte
+++ b/src/features/workbooks/components/list/TitleTableBodyCell.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   import { TableBodyCell } from 'flowbite-svelte';
 
   import type { WorkbookList } from '$features/workbooks/types/workbook';
@@ -20,7 +22,7 @@
   >
     <PublicationStatusLabel isPublished={workbook.isPublished} />
     <a
-      href="/workbooks/{getUrlSlugFrom(workbook)}"
+      href={resolve('/workbooks/[slug]', { slug: getUrlSlugFrom(workbook) })}
       class="flex-1 font-medium xs:text-lg text-primary-600 hover:underline dark:text-primary-500 truncate"
       aria-labelledby="View details for workbook: {workbook.title}"
     >
diff --git a/src/features/workbooks/components/list/WorkbookAuthorActionsCell.svelte b/src/features/workbooks/components/list/WorkbookAuthorActionsCell.svelte
index 08c1f127d..1d336bd1a 100644
--- a/src/features/workbooks/components/list/WorkbookAuthorActionsCell.svelte
+++ b/src/features/workbooks/components/list/WorkbookAuthorActionsCell.svelte
@@ -1,5 +1,7 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
   import { enhance } from '$app/forms';
+
   import { TableBodyCell } from 'flowbite-svelte';
 
   import type { Roles } from '$lib/types/user';
@@ -22,7 +24,7 @@
     class="flex justify-center items-center space-x-3 min-w-[96px] max-w-[120px] text-gray-700 dark:text-gray-300"
   >
     {#if canEdit(userId, workbook.authorId, role, workbook.isPublished)}
-      <a href="/workbooks/edit/{getUrlSlugFrom(workbook)}">編集</a>
+      <a href={resolve('/workbooks/edit/[slug]', { slug: getUrlSlugFrom(workbook) })}>編集</a>
     {/if}
 
     {#if canDelete(userId, workbook.authorId)}
diff --git a/src/features/workbooks/components/shared/WorkbookLink.svelte b/src/features/workbooks/components/shared/WorkbookLink.svelte
index 00c734053..299bbeb31 100644
--- a/src/features/workbooks/components/shared/WorkbookLink.svelte
+++ b/src/features/workbooks/components/shared/WorkbookLink.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   interface Props {
     workBookId: number;
     title: string;
@@ -8,7 +10,7 @@
 </script>
 
 <a
-  href="/workbooks/{workBookId}"
+  href={resolve('/workbooks/[slug]', { slug: String(workBookId) })}
   class="text-sm font-medium text-primary-600 hover:underline dark:text-primary-500"
   onclick={(e) => e.stopPropagation()}
   onpointerdown={(e) => e.stopPropagation()}
diff --git a/src/lib/components/AuthForm.svelte b/src/lib/components/AuthForm.svelte
index fdc44974d..e3f18979b 100644
--- a/src/lib/components/AuthForm.svelte
+++ b/src/lib/components/AuthForm.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
   import { tick } from 'svelte';
   import { goto } from '$app/navigation';
+  import { resolve } from '$app/paths';
 
   import { Card, Button, Label, Input, Hr } from 'flowbite-svelte';
 
@@ -17,7 +18,7 @@
     // GUEST_USER_PASSWORD_FOR_LOCAL,
     LOGIN_LABEL,
   } from '$lib/constants/forms';
-  import { HOME_PAGE, LOGIN_PAGE, FORGOT_PASSWORD_PAGE } from '$lib/constants/navbar-links';
+  import { HOME_PAGE, FORGOT_PASSWORD_PAGE, LOGIN_PAGE } from '$lib/constants/navbar-links';
 
   interface Props {
     // FIXME: 構造体に相当するものを利用した方が拡張・修正がしやすくなるかもしれせまん
@@ -27,7 +28,7 @@
     submitButtonLabel: string;
     confirmationMessage: string;
     alternativePageName: string;
-    alternativePageLink: string;
+    alternativePageLink: '/login' | '/signup';
   }
 
   let {
@@ -41,6 +42,13 @@
 
   const { form, message, errors, submitting, enhance } = formProperties;
 
+  // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+  const homeHref = resolve(HOME_PAGE);
+  // @ts-expect-error svelte-check TS2554: same declaration merging issue
+  const forgotPasswordHref = resolve(FORGOT_PASSWORD_PAGE);
+  // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+  const alternativeHref = $derived(resolve(alternativePageLink));
+
   let isSubmitting = $state(false);
 
   async function handleLoginAsGuest(event: Event) {
@@ -80,7 +88,7 @@
       }
 
       // FIXME: ログイン前のページに戻れるようにする
-      await goto(HOME_PAGE);
+      await goto(homeHref);
     } catch (error) {
       console.error('Failed to login as a guest: ', error);
     } finally {
@@ -202,7 +210,7 @@
           <!-- <Checkbox>Remember me</Checkbox> -->
 
           <a
-            href={FORGOT_PASSWORD_PAGE}
+            href={forgotPasswordHref}
             class="ml-auto text-sm text-primary-700 hover:underline dark:text-primary-500"
           >
             パスワードを忘れましたか?
@@ -216,10 +224,7 @@
 
       <div class="text-sm font-medium text-gray-500 dark:text-gray-300">
         {confirmationMessage}
-        <a
-          href={alternativePageLink}
-          class="text-primary-700 hover:underline dark:text-primary-500"
-        >
+        <a href={alternativeHref} class="text-primary-700 hover:underline dark:text-primary-500">
           {alternativePageName}
         </a>
       </div>
diff --git a/src/lib/components/ExternalLinkWrapper.svelte b/src/lib/components/ExternalLinkWrapper.svelte
index 49bdd4ecd..b826eb731 100644
--- a/src/lib/components/ExternalLinkWrapper.svelte
+++ b/src/lib/components/ExternalLinkWrapper.svelte
@@ -29,7 +29,7 @@
   class={`${useInlineFlex ? 'inline-flex' : ''} items-center font-medium ${textSize} text-primary-600 hover:underline ${textColorInDarkMode}`}
   aria-label={ariaLabel}
   target="_blank"
-  rel="noreferrer"
+  rel="noreferrer external"
 >
   <span class={`${textOverflow} truncate`}>
     {description}
diff --git a/src/lib/components/Header.svelte b/src/lib/components/Header.svelte
index 31e8f0130..b229d28b6 100644
--- a/src/lib/components/Header.svelte
+++ b/src/lib/components/Header.svelte
@@ -50,7 +50,7 @@
       {@render navLiForDropdown('nav-dashboard', '管理画面')}
 
       <Dropdown triggeredBy="#nav-dashboard" simple class="w-48 z-20">
-        {#each navbarDashboardLinks as navbarDashboardLink}
+        {#each navbarDashboardLinks as navbarDashboardLink (navbarDashboardLink.path)}
           <DropdownItem href={navbarDashboardLink.path}>
             {navbarDashboardLink.title}
           </DropdownItem>
@@ -59,7 +59,7 @@
     {/if}
 
     <!-- Internal Links -->
-    {#each navbarLinks as navbarLink}
+    {#each navbarLinks as navbarLink (navbarLink.path)}
       <NavLi
         href={navbarLink.path}
         class="flex items-center"
@@ -107,7 +107,7 @@
     {@render navLiForDropdown('nav-external-links', '外部リンク')}
 
     <Dropdown triggeredBy="#nav-external-links" simple class="w-48 z-20">
-      {#each externalLinks as externalLink}
+      {#each externalLinks as externalLink (externalLink.path)}
         <DropdownItem href={externalLink.path} target="_blank">
           {externalLink.title}
         </DropdownItem>
diff --git a/src/lib/components/LabelWithTooltips.svelte b/src/lib/components/LabelWithTooltips.svelte
index f2de2b354..e9d39933c 100644
--- a/src/lib/components/LabelWithTooltips.svelte
+++ b/src/lib/components/LabelWithTooltips.svelte
@@ -25,7 +25,7 @@
       {#if typeof tooltipContents === 'string'}
         {tooltipContents}
       {:else}
-        {#each tooltipContents as tooltipContent}
+        {#each tooltipContents as tooltipContent, i (i)}
           {tooltipContent}<br />
         {/each}
       {/if}
diff --git a/src/lib/components/SubmissionStatus/UpdatingDropdown.svelte b/src/lib/components/SubmissionStatus/UpdatingDropdown.svelte
index 6993d6e92..a6ed99a42 100644
--- a/src/lib/components/SubmissionStatus/UpdatingDropdown.svelte
+++ b/src/lib/components/SubmissionStatus/UpdatingDropdown.svelte
@@ -20,6 +20,7 @@
 -->
 <script lang="ts">
   import { enhance } from '$app/forms';
+  import { resolve } from '$app/paths';
 
   import { Dropdown, DropdownItem, DropdownDivider } from 'flowbite-svelte';
   import Check from '@lucide/svelte/icons/check';
@@ -42,6 +43,11 @@
 
   let { taskResult, isLoggedIn, onupdate }: Props = $props();
 
+  // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+  const signupHref = resolve(SIGNUP_PAGE);
+  // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+  const loginHref = resolve(LOGIN_PAGE);
+
   const componentId = Math.random().toString(36).substring(2);
   let isInBottomHalf = $state(false);
 
@@ -198,7 +204,7 @@
   class="w-32 z-50 border border-gray-200 dark:border-gray-100"
 >
   {#if isLoggedIn}
-    {#each submissionStatusOptions as submissionStatus}
+    {#each submissionStatusOptions as submissionStatus (submissionStatus.innerName)}
       <DropdownItem onclick={() => handleClick(submissionStatus)} class="rounded-md">
         <div
           class="flex items-center justify-between w-full text-gray-700 dark:text-gray-300 hover:text-gray-900 dark:hover:text-white"
@@ -211,9 +217,9 @@
       </DropdownItem>
     {/each}
   {:else}
-    <DropdownItem href={SIGNUP_PAGE} class="rounded-md">アカウント作成</DropdownItem>
+    <DropdownItem href={signupHref} class="rounded-md">アカウント作成</DropdownItem>
     <DropdownDivider />
-    <DropdownItem href={LOGIN_PAGE} class="rounded-md">ログイン</DropdownItem>
+    <DropdownItem href={loginHref} class="rounded-md">ログイン</DropdownItem>
   {/if}
 </Dropdown>
 
diff --git a/src/lib/components/TagForm.svelte b/src/lib/components/TagForm.svelte
index aa8dc2a33..ac007fe98 100644
--- a/src/lib/components/TagForm.svelte
+++ b/src/lib/components/TagForm.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   import {
     Table,
     TableBody,
@@ -26,11 +28,14 @@
   let name: string = $state(tag.name);
 
   //export const isAdmin: boolean; // Admin権限がある場合は、編集リンクを表示する
+
+  // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+  const tagsHref = resolve('/(admin)/tags');
 </script>
 
 <!-- TODO: レスポンシブ対応 -->
 <!-- TODO: Tagを修正するためのフォームを用意する -->
-<a href="/tags"> タグ一覧へもどる（パンくずリストにしたい） </a>
+<a href={tagsHref}> タグ一覧へもどる（パンくずリストにしたい） </a>
 <br />
 Edit Tag
 <form method="POST" action="/tags?/update">
@@ -83,21 +88,21 @@ Edit Tag
   </TableHead>
 
   <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-    {#each tasks as task}
+    {#each tasks as task (task.task_id)}
       <TableBodyRow>
         <TableBodyCell>
           <a
             href="{ATCODER_BASE_CONTEST_URL}/{task.contest_id}"
             class="font-medium text-primary-600 hover:underline dark:text-primary-500"
             target="_blank"
-            rel="noreferrer"
+            rel="noreferrer external"
           >
             {getContestNameLabel(task.contest_id)}
           </a>
         </TableBodyCell>
         <TableBodyCell>
           <a
-            href="/problems/{task.task_id}"
+            href={resolve('/problems/[slug]', { slug: task.task_id })}
             class="font-medium text-primary-600 hover:underline dark:text-primary-500"
           >
             {task.title}
@@ -105,7 +110,7 @@ Edit Tag
         </TableBodyCell>
         <TableBodyCell>
           <a
-            href="/tasks/{task.task_id}"
+            href={resolve('/(admin)/tasks/[task_id]', { task_id: task.task_id })}
             class="font-medium text-primary-600 hover:underline dark:text-primary-500"
           >
             編集
diff --git a/src/lib/components/TagListForEdit.svelte b/src/lib/components/TagListForEdit.svelte
index 3cc64e9b4..58c8551c6 100644
--- a/src/lib/components/TagListForEdit.svelte
+++ b/src/lib/components/TagListForEdit.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   import {
     Table,
     TableBody,
@@ -10,6 +12,7 @@
   } from 'flowbite-svelte';
   import type { Tag } from '$lib/types/tag';
   //import { ATCODER_BASE_CONTEST_URL } from '$lib/constants/urls';
+
   import { newline } from '$lib/utils/newline';
   //import { tasks } from '../server/sample_data';
 
@@ -35,11 +38,11 @@
     <TableHeadCell class="w-1/8"></TableHeadCell>
   </TableHead>
   <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-    {#each tags as tag}
+    {#each tags as tag (tag.id)}
       <TableBodyRow>
         <TableBodyCell class="p-3">
           <Label>
-            {#each newline(tag.name, 10) as line}
+            {#each newline(tag.name, 10) as line, i (i)}
               {line}<br />
             {/each}
           </Label>
@@ -57,7 +60,7 @@
         </TableBodyCell>
         <TableBodyCell>
           {#if tag.id !== 'undefined'}
-            <a href="/tags/{tag.id}">編集</a>
+            <a href={resolve('/(admin)/tags/[tag_id]', { tag_id: tag.id })}>編集</a>
           {:else}
             未登録
           {/if}
diff --git a/src/lib/components/TaskGradeList.svelte b/src/lib/components/TaskGradeList.svelte
index c9c955865..f8b0d7a6d 100644
--- a/src/lib/components/TaskGradeList.svelte
+++ b/src/lib/components/TaskGradeList.svelte
@@ -1,6 +1,4 @@
 <script lang="ts">
-  import { run } from 'svelte/legacy';
-
   import TaskList from '$lib/components/TaskList.svelte';
 
   import type { TaskResults, TaskResult } from '$lib/types/task';
@@ -15,22 +13,17 @@
   let { taskResults, isAdmin, isLoggedIn }: Props = $props();
 
   // TODO: 共通する内容はutilsに移動させる。
-  let taskResultsForEachGrade = $state(new Map());
-
-  // HACK: $effectだと更新されないため、やむなくrunを使用。
-  run(() => {
-    taskResultsForEachGrade = new Map();
-
-    taskGradeValues.map((grade) => {
-      taskResultsForEachGrade.set(
+  const taskResultsForEachGrade = $derived(
+    new Map(
+      taskGradeValues.map((grade): [TaskGrade, TaskResults] => [
         grade,
         taskResults.filter((taskResult: TaskResult) => taskResult.grade === grade),
-      );
-    });
-  });
+      ]),
+    ),
+  );
 
   const countTasks = (taskGrade: TaskGrade) => {
-    return taskResultsForEachGrade.get(taskGrade).length;
+    return taskResultsForEachGrade.get(taskGrade)?.length ?? 0;
   };
 
   const isShowTaskList = (isAdmin: boolean, taskGrade: TaskGrade): boolean => {
@@ -46,13 +39,13 @@
   };
 </script>
 
-{#each taskGradeValues as taskGrade}
+{#each taskGradeValues as taskGrade (taskGrade)}
   <!-- Pendingは、Adminのみ表示。-->
   <!-- HACK: Svelteでcontinueに相当する構文は確認できず(2024年1月時点)。 -->
   {#if countTasks(taskGrade) && isShowTaskList(isAdmin, taskGrade)}
     <TaskList
       grade={taskGrade}
-      taskResults={taskResultsForEachGrade.get(taskGrade)}
+      taskResults={taskResultsForEachGrade.get(taskGrade)!}
       {isAdmin}
       {isLoggedIn}
     />
diff --git a/src/lib/components/TaskGrades/GradeGuidelineTable.svelte b/src/lib/components/TaskGrades/GradeGuidelineTable.svelte
index 694460119..864cca47e 100644
--- a/src/lib/components/TaskGrades/GradeGuidelineTable.svelte
+++ b/src/lib/components/TaskGrades/GradeGuidelineTable.svelte
@@ -41,7 +41,7 @@
     </TableHead>
 
     <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-      {#each gradeGuidelineTableData as { point, task, lowerGrade, upperGrade }}
+      {#each gradeGuidelineTableData as { point, task, lowerGrade, upperGrade } (point)}
         <TableBodyRow>
           <TableBodyCell class="text-sm xs:text-md text-center py-3">{point}</TableBodyCell>
           <TableBodyCell class="text-center py-3 hidden sm:table-cell">{task}</TableBodyCell>
diff --git a/src/lib/components/TaskList.svelte b/src/lib/components/TaskList.svelte
index 6459925cb..bbfa66303 100644
--- a/src/lib/components/TaskList.svelte
+++ b/src/lib/components/TaskList.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   import {
     AccordionItem,
     Accordion,
@@ -95,7 +97,7 @@
         </TableHead>
 
         <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-          {#each taskResults as taskResult}
+          {#each taskResults as taskResult (taskResult.task_id)}
             <TableBodyRow
               id={taskResult.contest_id + '-' + taskResult.task_id}
               class={getBackgroundColorFrom(taskResult.status_name)}
@@ -128,7 +130,7 @@
                 {#if isAdmin}
                   <div class="flex justify-center items-center px-0">
                     <a
-                      href="/tasks/{taskResult.task_id}"
+                      href={resolve('/(admin)/tasks/[task_id]', { task_id: taskResult.task_id })}
                       class="font-medium text-primary-600 hover:underline dark:text-gray-300"
                     >
                       編集
diff --git a/src/lib/components/TaskListForEdit.svelte b/src/lib/components/TaskListForEdit.svelte
index 6efbeda40..506439a65 100644
--- a/src/lib/components/TaskListForEdit.svelte
+++ b/src/lib/components/TaskListForEdit.svelte
@@ -37,26 +37,26 @@
     <TableHeadCell class="w-1/8"></TableHeadCell>
   </TableHead>
   <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-    {#each importContests as importContest}
+    {#each importContests as importContest (importContest.id)}
       {#if importContest.tasks.length > 0}
         <TableBodyRow>
           <TableBodyCell class="p-3">
             <Label>
-              {#each newline(getContestNameLabel(importContest.id), 10) as line}
+              {#each newline(getContestNameLabel(importContest.id), 10) as line, i (i)}
                 {line}<br />
               {/each}
             </Label>
           </TableBodyCell>
           <TableBodyCell>
             <Label>
-              {#each newline(importContest.title, 28) as line}
+              {#each newline(importContest.title, 28) as line, i (i)}
                 {line}<br />
               {/each}
             </Label>
           </TableBodyCell>
 
           <TableBodyCell>
-            {#each importContest.tasks as importTask}
+            {#each importContest.tasks as importTask (importTask.task_id)}
               <li>{importTask.title}</li>
             {/each}
           </TableBodyCell>
diff --git a/src/lib/components/TaskListSorted.svelte b/src/lib/components/TaskListSorted.svelte
index 319e10f12..2264053b6 100644
--- a/src/lib/components/TaskListSorted.svelte
+++ b/src/lib/components/TaskListSorted.svelte
@@ -1,4 +1,6 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   import {
     Img,
     Table,
@@ -32,7 +34,7 @@
     </TableHead>
 
     <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-      {#each taskResults as taskResult}
+      {#each taskResults as taskResult (taskResult.task_id)}
         <TableBodyRow>
           <TableBodyCell class="p-3">
             <Img
@@ -43,7 +45,7 @@
           </TableBodyCell>
           <TableBodyCell>
             <a
-              href="/problems/{taskResult.task_id}"
+              href={resolve('/problems/[slug]', { slug: taskResult.task_id })}
               class="font-medium text-primary-600 hover:underline dark:text-primary-500"
             >
               {removeTaskIndexFromTitle(taskResult.title, taskResult.task_table_index)}
diff --git a/src/lib/components/TaskSearchBox.svelte b/src/lib/components/TaskSearchBox.svelte
index 34fabe4c9..21651585e 100644
--- a/src/lib/components/TaskSearchBox.svelte
+++ b/src/lib/components/TaskSearchBox.svelte
@@ -168,7 +168,7 @@
 
 {#if filteredTasks.length}
   <Listgroup>
-    {#each filteredTasks as task, index}
+    {#each filteredTasks as task, index (task.task_id)}
       <!-- See: -->
       <!-- WHY: Use a custom <li> element with conditional classes for highlighting, due not to be able to find attribute. -->
       <li
diff --git a/src/lib/components/ThermometerProgressBar.svelte b/src/lib/components/ThermometerProgressBar.svelte
index 582950bb8..9d8251e33 100644
--- a/src/lib/components/ThermometerProgressBar.svelte
+++ b/src/lib/components/ThermometerProgressBar.svelte
@@ -17,8 +17,6 @@
 
   let { workBookTasks = [], taskResults, width = 'w-7/12 md:w-8/12 lg:w-9/12' }: Props = $props();
 
-  let submissionRatios: SubmissionRatios = $state([]);
-  let submissionCounts: SubmissionCounts = $state([]);
   let progressBarId = `progress-bar-${Math.floor(Math.random() * 10000)}`;
 
   const filteredStatuses = submission_statuses.filter((status) => status.status_name !== 'ns');
@@ -44,8 +42,8 @@
     'shadow-none flex flex-col text-center whitespace-nowrap text-white justify-center';
 
   // TODO: ユーザの設定に応じて、ACかどうかの判定を変更できるようにする
-  $effect(() => {
-    submissionRatios = filteredStatuses.map((status) => {
+  let submissionRatios: SubmissionRatios = $derived(
+    filteredStatuses.map((status) => {
       const name = status.status_name;
       const ratioPercent = getRatioPercent(taskResults, name);
 
@@ -54,10 +52,10 @@
         ratioPercent: ratioPercent,
         color: status.background_color,
       };
-    });
-  });
-  $effect(() => {
-    submissionCounts = filteredStatuses.map((status) => {
+    }),
+  );
+  let submissionCounts: SubmissionCounts = $derived(
+    filteredStatuses.map((status) => {
       const name = status.status_name;
       const taskCount = getTaskCount(taskResults, name);
       const ratioPercent = getRatioPercent(taskResults, name);
@@ -67,8 +65,8 @@
         count: taskCount,
         ratioPercent: ratioPercent,
       };
-    });
-  });
+    }),
+  );
 </script>
 
 <!-- HACK: Flowbite Svelte にある Progressbar では 回答状況に合わせた内訳を表示できないので、HTML + tailwindcss で実装 -->
@@ -79,7 +77,7 @@
   <div class="rounded-full h-6">
     <span id={progressBarId}>
       <div class="overflow-hidden h-6 flex rounded-full bg-white dark:bg-gray-800">
-        {#each submissionRatios as submissionRatio}
+        {#each submissionRatios as submissionRatio (submissionRatio.name)}
           <div
             style="width: {submissionRatio.ratioPercent}%"
             class={`${baseAttributes} ${submissionRatio.color}`}
@@ -96,7 +94,7 @@
   placement="top-start"
   class={`max-w-[200px] ${TOOLTIP_CLASS_BASE}`}
 >
-  {#each submissionCounts as submissionCount}
+  {#each submissionCounts as submissionCount (submissionCount.name)}
     <div class="flex">
       <span class="w-14">{submissionCount.name}</span>
       <span class="w-2">: </span>
diff --git a/src/routes/(admin)/account_transfer/+page.svelte b/src/routes/(admin)/account_transfer/+page.svelte
index 569ee8e6a..06f06795e 100644
--- a/src/routes/(admin)/account_transfer/+page.svelte
+++ b/src/routes/(admin)/account_transfer/+page.svelte
@@ -22,12 +22,11 @@
   import type { FloatingMessages } from '$lib/types/floating_message';
 
   interface Props {
-    formAction?: string;
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     data: any;
   }
 
-  let { formAction = 'account_transfer', data }: Props = $props();
+  let { data }: Props = $props();
 
   const { form, errors, message, submitting, enhance } = superForm(data.form);
 
@@ -63,7 +62,7 @@
 <ContainerWrapper>
   <HeadingOne title="アカウント移行" />
 
-  <form method="POST" class="flex flex-col gap-4" action={formAction} use:enhance>
+  <form method="POST" class="flex flex-col gap-4" use:enhance>
     <div class="dark:text-gray-300">
       新しく作成された空のアカウントに、旧アカウントの回答データをコピーできます。
     </div>
@@ -124,7 +123,7 @@
 
   <!-- ステータス表示 -->
   <div class="p-4 space-y-4 dark:text-gray-300">
-    {#each accountTransferMessages as accountTransferMessage}
+    {#each accountTransferMessages as accountTransferMessage, i (i)}
       <div class="flex items-center space-x-2">
         {#if accountTransferMessage.status}
           <!-- 成功時のアイコン -->
diff --git a/src/routes/(admin)/workbooks/order/_components/ColumnSelector.svelte b/src/routes/(admin)/workbooks/order/_components/ColumnSelector.svelte
index 7e11fb38d..1042f1431 100644
--- a/src/routes/(admin)/workbooks/order/_components/ColumnSelector.svelte
+++ b/src/routes/(admin)/workbooks/order/_components/ColumnSelector.svelte
@@ -28,7 +28,7 @@
 </script>
 
 <div class="flex flex-wrap gap-2">
-  {#each options as option}
+  {#each options as option (option.value)}
     {@const isSelected = selected.includes(option.value)}
 
     <button
diff --git a/src/routes/(admin)/workbooks/order/_components/KanbanBoard.svelte b/src/routes/(admin)/workbooks/order/_components/KanbanBoard.svelte
index 1170c10cb..24c28ad88 100644
--- a/src/routes/(admin)/workbooks/order/_components/KanbanBoard.svelte
+++ b/src/routes/(admin)/workbooks/order/_components/KanbanBoard.svelte
@@ -53,10 +53,13 @@
   ]);
 
   function updateUrl() {
-    replaceState(
-      buildUpdatedUrl($page.url, activeTab, selectedSolutionCategories, selectedGrades),
-      {},
+    const updatedUrl = buildUpdatedUrl(
+      $page.url,
+      activeTab,
+      selectedSolutionCategories,
+      selectedGrades,
     );
+    replaceState(updatedUrl, {});
   }
 
   let allItems = $state<Record<string, KanbanColumns>>(
@@ -150,7 +153,7 @@
     <!-- Note: Snippets are intentional: extracting these as components would require passing too many props. -->
     {#snippet solutionBoard()}
       <div class="flex gap-3 overflow-x-auto pb-4">
-        {#each displayedSolutionCategories as column}
+        {#each displayedSolutionCategories as column (column)}
           <KanbanColumn
             columnId={column}
             label={TAB_CONFIGS['solution'].labelFn(column)}
@@ -163,7 +166,7 @@
 
     {#snippet curriculumBoard()}
       <div class="flex gap-3 overflow-x-auto pb-4">
-        {#each selectedGrades as column}
+        {#each selectedGrades as column (column)}
           <KanbanColumn
             columnId={column}
             label={TAB_CONFIGS['curriculum'].labelFn(column)}
diff --git a/src/routes/about/SectionSnippets.svelte b/src/routes/about/SectionSnippets.svelte
index df919288d..0d7e2d4fc 100644
--- a/src/routes/about/SectionSnippets.svelte
+++ b/src/routes/about/SectionSnippets.svelte
@@ -35,7 +35,7 @@
 <!-- TODO: Split files if needs. -->
 {#snippet coreFeatures()}
   <List tag="ul" class="text-gray-800 dark:text-gray-300 ml-6 space-y-1">
-    {#each features as feature}
+    {#each features as feature (feature.description)}
       <Li>{feature.description}</Li>
     {/each}
   </List>
@@ -137,7 +137,7 @@
 
 {#snippet developmentMembers()}
   <List tag="ul" class="text-gray-800 dark:text-gray-300 ml-6 space-y-1">
-    {#each members as member}
+    {#each members as member (member.account)}
       <Li>
         <ExternalLinkWrapper url={member.account} description={member.name} />
       </Li>
diff --git a/src/routes/problems/[slug]/+page.svelte b/src/routes/problems/[slug]/+page.svelte
index 7270366e5..b097ea511 100644
--- a/src/routes/problems/[slug]/+page.svelte
+++ b/src/routes/problems/[slug]/+page.svelte
@@ -33,7 +33,7 @@
   <a
     href={getTaskUrl(taskResult.contest_id, taskResult.task_id)}
     target="_blank"
-    rel="noreferrer"
+    rel="noreferrer external"
     class="flex flex-col items-center
     {getBackgroundColorFrom(taskResult.status_name)}
     border border-gray-200 rounded-lg max-w-lg mt-8 mb-8 mx-auto shadow md:flex-row md:max-w-xl dark:border-gray-700 dark:bg-gray-800 dark:hover:bg-gray-700"
@@ -61,7 +61,7 @@
   <!-- See: https://tailwindcss.com/docs/align-items -->
   <!-- See: https://bobbyhadz.com/blog/typescript-type-string-is-not-assignable-to-type -->
   <form method="post" class="flex flex-col items-center" use:enhance>
-    {#each buttons as button}
+    {#each buttons as button (button.status_name)}
       <SubmissionStatusButton
         value={button.status_name}
         textColor={button.text_color}
diff --git a/src/routes/users/[username]/+page.svelte b/src/routes/users/[username]/+page.svelte
index 1ab9698b5..459e1770e 100644
--- a/src/routes/users/[username]/+page.svelte
+++ b/src/routes/users/[username]/+page.svelte
@@ -1,7 +1,10 @@
 <script lang="ts">
+  import { resolve } from '$app/paths';
+
   import UserProfile from '$lib/components/UserProfile.svelte';
   import HeadingOne from '$lib/components/HeadingOne.svelte';
   import TaskListSorted from '$lib/components/TaskListSorted.svelte';
+  import { PROBLEMS_PAGE } from '$lib/constants/navbar-links';
 
   let { data } = $props();
 
@@ -9,6 +12,9 @@
   let atcoder_username = data.atcoder_username;
   let isLoggedIn = data.isLoggedIn;
   let taskResults = data.taskResults;
+
+  // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+  const problemsHref = resolve(PROBLEMS_PAGE);
 </script>
 
 <div class="container mx-auto w-1/4">
@@ -18,7 +24,7 @@
 <div class="container mx-auto w-5/6">
   {#if taskResults}
     <HeadingOne title="">
-      <a href="/problems">Problems</a>
+      <a href={problemsHref}>Problems</a>
     </HeadingOne>
     <TaskListSorted {taskResults} />
   {/if}
diff --git a/src/routes/workbooks/+page.svelte b/src/routes/workbooks/+page.svelte
index ba17d88da..c2ad4aba3 100644
--- a/src/routes/workbooks/+page.svelte
+++ b/src/routes/workbooks/+page.svelte
@@ -1,6 +1,8 @@
 <script lang="ts">
   import { onMount } from 'svelte';
   import { goto } from '$app/navigation';
+  import { resolve } from '$app/paths';
+
   import { Button, Tabs } from 'flowbite-svelte';
 
   import { Roles } from '$lib/types/user';
@@ -47,7 +49,9 @@
     const saved = sessionStorage.getItem(WORKBOOKS_URL_KEY);
 
     if (saved) {
-      goto(saved, { replaceState: true });
+      const savedUrl = new URL(saved, window.location.origin);
+      // @ts-expect-error svelte-check TS2554: AppTypes declaration merging causes RouteId to resolve as string, requiring params. Runtime behavior is correct.
+      goto(resolve(savedUrl.pathname) + savedUrl.search, { replaceState: true });
     }
   });
 
@@ -65,15 +69,18 @@
   };
 
   function handleTabChange(tab: WorkBookTab) {
-    goto(TAB_URL_BUILDERS[tab]());
+    // @ts-expect-error svelte-check TS2554: same declaration merging issue
+    goto(resolve(TAB_URL_BUILDERS[tab]()));
   }
 
   function handleGradeChange(grade: TaskGrade) {
-    goto(buildWorkbooksUrl(WorkBookTab.CURRICULUM, grade));
+    // @ts-expect-error svelte-check TS2554: same declaration merging issue
+    goto(resolve(buildWorkbooksUrl(WorkBookTab.CURRICULUM, grade)));
   }
 
   function handleCategoryChange(category: SolutionCategory) {
-    goto(buildWorkbooksUrl(WorkBookTab.SOLUTION, undefined, category));
+    // @ts-expect-error svelte-check TS2554: same declaration merging issue
+    goto(resolve(buildWorkbooksUrl(WorkBookTab.SOLUTION, undefined, category)));
   }
 </script>
 
diff --git a/src/routes/workbooks/[slug]/+page.svelte b/src/routes/workbooks/[slug]/+page.svelte
index 9879cb051..ba9712a66 100644
--- a/src/routes/workbooks/[slug]/+page.svelte
+++ b/src/routes/workbooks/[slug]/+page.svelte
@@ -31,11 +31,7 @@
 
   let workBook = data.workBook;
   let workBookTasks: WorkBookTaskBase[] = $state([]);
-  let taskResults: Map<string, TaskResult> = $state(new Map());
-
-  $effect(() => {
-    taskResults = data.taskResults;
-  });
+  let taskResults: Map<string, TaskResult> = $derived(data.taskResults);
 
   let isLoggedIn = data.isLoggedIn;
 
@@ -159,7 +155,7 @@
           <TableHeadCell class="w-14 text-center px-0.5">一言</TableHeadCell>
         </TableHead>
         <TableBody class="divide-y divide-gray-200 dark:divide-gray-700">
-          {#each workBookTasks as workBookTask}
+          {#each workBookTasks as workBookTask (workBookTask.taskId)}
             <TableBodyRow
               id={getUniqueIdUsing(workBookTask.taskId)}
               class={getBackgroundColorFrom(getTaskResult(workBookTask.taskId).status_name)}