diff --git a/.gitignore b/.gitignore
index 7b769d1b..db5c4cc7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -57,4 +57,3 @@ lab/output/
 
 # opensrc - source code for packages
 opensrc/
-AGENTS.md
diff --git a/AGENTS.md b/AGENTS.md
new file mode 100644
index 00000000..0b35df15
--- /dev/null
+++ b/AGENTS.md
@@ -0,0 +1,42 @@
+# AGENTS.md
+
+Instructions for AI coding agents working with this codebase.
+
+## Communication
+
+- Do not present guesses as facts. Label uncertainty explicitly.
+- If you were wrong, say so briefly and correct it directly.
+- Do not argue defensively or justify an incorrect claim before correcting it.
+- Keep the tone neutral and practical. Avoid condescension.
+- Use polite Japanese (`です`/`ます`) when responding in Japanese.
+- Do not use unnatural validation, praise, or evaluative filler such as telling the user their reaction is valid or that an idea is highly effective unless that judgment is necessary.
+- Do not end responses by hinting at additional useful context without giving it. If adjacent context matters, include it briefly in the same response.
+- Do not present a conclusion as if it were obvious only after the user suggests it. If you have a concrete conclusion, state it first and directly.
+- If the user questions a factual claim, do not double down from memory. Check the code, docs, or other primary evidence before answering.
+- Do not use vague hedge words to leave yourself escape hatches. State what is confirmed, state what is unconfirmed, and make the condition explicit when an answer depends on one.
+- When blocked by environment limits, state the limit plainly and move to the best available workaround.
+
+For all other project-specific guidance, conventions, and workflow details, see `CLAUDE.md`.
+
+<!-- opensrc:start -->
+
+## Source Code Reference
+
+Source code for dependencies is available in `opensrc/` for deeper understanding of implementation details.
+
+See `opensrc/sources.json` for the list of available packages and their versions.
+
+Use this source code when you need to understand how a package works internally, not just its types/interface.
+
+### Fetching Additional Source Code
+
+To fetch source code for a package or repository you need to understand, run:
+
+```bash
+npx opensrc <package>           # npm package (e.g., npx opensrc zod)
+npx opensrc pypi:<package>      # Python package (e.g., npx opensrc pypi:requests)
+npx opensrc crates:<package>    # Rust crate (e.g., npx opensrc crates:serde)
+npx opensrc <owner>/<repo>      # GitHub repo (e.g., npx opensrc vercel/ai)
+```
+
+<!-- opensrc:end -->
diff --git a/app/services/durably.server.ts b/app/services/durably.server.ts
index cf1b4567..f8a9debb 100644
--- a/app/services/durably.server.ts
+++ b/app/services/durably.server.ts
@@ -2,6 +2,7 @@ import { createDurably, createDurablyHandler } from '@coji/durably'
 import SQLite from 'better-sqlite3'
 import { SqliteDialect } from 'kysely'
 import { getSession, getUserOrganizations } from '~/app/libs/auth.server'
+import { backfillJob } from '~/app/services/jobs/backfill.server'
 import { crawlJob } from '~/app/services/jobs/crawl.server'
 import { recalculateJob } from '~/app/services/jobs/recalculate.server'
 
@@ -17,6 +18,7 @@ function createDurablyInstance() {
     leaseMs: 300_000, // 5 minutes (default 30s is too short for large orgs)
     leaseRenewIntervalMs: 30_000,
     jobs: {
+      backfill: backfillJob,
       crawl: crawlJob,
       recalculate: recalculateJob,
     },
diff --git a/app/services/jobs/backfill.server.ts b/app/services/jobs/backfill.server.ts
new file mode 100644
index 00000000..6cd0a253
--- /dev/null
+++ b/app/services/jobs/backfill.server.ts
@@ -0,0 +1,57 @@
+import { defineJob } from '@coji/durably'
+import { z } from 'zod'
+import type { OrganizationId } from '~/app/types/organization'
+import { getOrganization } from '~/batch/db/queries'
+import { backfillRepo } from '~/batch/github/backfill-repo'
+
+export const backfillJob = defineJob({
+  name: 'backfill',
+  input: z.object({
+    organizationId: z.string(),
+    files: z.boolean().default(false),
+  }),
+  output: z.object({
+    repositoryCount: z.number(),
+  }),
+  run: async (step, input) => {
+    const orgId = input.organizationId as OrganizationId
+
+    const organization = await step.run('load-organization', async () => {
+      step.progress(0, 0, 'Loading organization...')
+      const org = await getOrganization(orgId)
+      if (!org.integration?.privateToken) {
+        throw new Error('No integration or token configured')
+      }
+      return {
+        repositories: org.repositories,
+      }
+    })
+
+    const org = await getOrganization(orgId)
+    const token = org.integration?.privateToken
+    if (!token) {
+      throw new Error('No integration token')
+    }
+
+    const repoCount = organization.repositories.length
+
+    for (let i = 0; i < organization.repositories.length; i++) {
+      const repository = organization.repositories[i]
+      const repoLabel = `${repository.owner}/${repository.repo}`
+
+      await step.run(`backfill:${repoLabel}`, async () => {
+        step.progress(i + 1, repoCount, `Backfilling ${repoLabel}...`)
+        await backfillRepo(
+          orgId,
+          repository,
+          { privateToken: token },
+          {
+            files: input.files,
+          },
+        )
+      })
+    }
+
+    return { repositoryCount: repoCount }
+  },
+})
diff --git a/app/services/jobs/crawl.server.ts b/app/services/jobs/crawl.server.ts
index 2f3978da..d694e99d 100644
--- a/app/services/jobs/crawl.server.ts
+++ b/app/services/jobs/crawl.server.ts
@@ -1,5 +1,4 @@
 import { defineJob } from '@coji/durably'
-import { sql } from 'kysely'
 import { z } from 'zod'
 import { clearOrgCache } from '~/app/services/cache.server'
 import { getTenantDb } from '~/app/services/tenant-db.server'
@@ -146,9 +145,7 @@ export const crawlJob = defineJob({
     // Skip analyze if no updates (and not a refresh)
     if (!input.refresh && updatedPrNumbers.size === 0) {
       step.log.info('No updated PRs, skipping analyze.')
-      await step.run('finalize', async () => {
-        const tenantDb = getTenantDb(orgId)
-        await sql`PRAGMA wal_checkpoint(PASSIVE)`.execute(tenantDb)
+      await step.run('finalize', () => {
         clearOrgCache(orgId)
       })
       return { fetchedRepos: repoCount, pullCount: 0 }
diff --git a/app/services/jobs/run-in-worker.test.ts b/app/services/jobs/run-in-worker.test.ts
index a2838a3f..447c7463 100644
--- a/app/services/jobs/run-in-worker.test.ts
+++ b/app/services/jobs/run-in-worker.test.ts
@@ -13,10 +13,10 @@ describe('getWorkerRuntime', () => {
   })
 
   test('uses ts worker files in development', () => {
-    const runtime = getWorkerRuntime('upsert-worker', 'development')
+    const runtime = getWorkerRuntime('analyze-worker', 'development')
 
     expect(runtime.workerPath).toBe(
-      path.resolve(process.cwd(), 'app/services/jobs/upsert-worker.ts'),
+      path.resolve(process.cwd(), 'app/services/jobs/analyze-worker.ts'),
     )
     expect(runtime.workerOptions.execArgv).toEqual(['--import', 'tsx'])
   })
diff --git a/app/services/jobs/run-in-worker.ts b/app/services/jobs/run-in-worker.ts
index 72aca7e2..a4c46388 100644
--- a/app/services/jobs/run-in-worker.ts
+++ b/app/services/jobs/run-in-worker.ts
@@ -34,22 +34,7 @@ export function runAnalyzeInWorker<T>(
 ): Promise<T> {
   return runWorker<T>('analyze-worker', input, options)
 }
-
-interface UpsertWorkerInput<TPull, TReview, TReviewer> {
-  organizationId: string
-  pulls: TPull[]
-  reviews: TReview[]
-  reviewers: TReviewer[]
-}
-
-export function runUpsertInWorker<TPull, TReview, TReviewer>(
-  input: UpsertWorkerInput<TPull, TReview, TReviewer>,
-  options?: RunWorkerOptions,
-): Promise<{ ok: true }> {
-  return runWorker<{ ok: true }>('upsert-worker', input, options)
-}
-
-type WorkerEntrypoint = 'analyze-worker' | 'upsert-worker'
+type WorkerEntrypoint = 'analyze-worker'
 const SQLITE_BUSY_RETRY_LIMIT = 3
 const SQLITE_BUSY_RETRY_DELAYS_MS = [150, 400, 1000]
 
diff --git a/app/services/jobs/shared-steps.server.ts b/app/services/jobs/shared-steps.server.ts
index c0fa4a90..26d6d09b 100644
--- a/app/services/jobs/shared-steps.server.ts
+++ b/app/services/jobs/shared-steps.server.ts
@@ -2,21 +2,23 @@
  * crawl と recalculate ジョブで共有する analyze → upsert → classify → export → finalize ステップ群
  */
 import type { StepContext } from '@coji/durably'
-import { sql, type Selectable } from 'kysely'
+import type { Selectable } from 'kysely'
 import { clearOrgCache } from '~/app/services/cache.server'
-import { getTenantDb, type TenantDB } from '~/app/services/tenant-db.server'
+import type { TenantDB } from '~/app/services/tenant-db.server'
 import type { OrganizationId } from '~/app/types/organization'
 import {
   exportPulls,
   exportReviewResponses,
 } from '~/batch/bizlogic/export-spreadsheet'
+import { upsertAnalyzedData } from '~/batch/db'
 import type {
   AnalyzedReview,
   AnalyzedReviewResponse,
   AnalyzedReviewer,
 } from '~/batch/github/types'
 import { classifyPullRequests } from '~/batch/usecases/classify-pull-requests'
-import { runAnalyzeInWorker, runUpsertInWorker } from './run-in-worker'
+import type { SqliteBusyEvent } from './run-in-worker'
+import { runAnalyzeInWorker } from './run-in-worker'
 
 interface AnalyzeResult {
   pulls: Selectable<TenantDB.PullRequests>[]
@@ -54,6 +56,23 @@ function formatDurationMs(durationMs: number) {
   return `${(durationMs / 1000).toFixed(1)}s`
 }
 
+function summarizeBusyEvents(events: SqliteBusyEvent[]) {
+  if (events.length === 0) return null
+
+  const retries = events.filter((event) => !event.gaveUp)
+  const gaveUp = events.filter((event) => event.gaveUp)
+  const totalWaitMs = retries.reduce((sum, event) => sum + event.delayMs, 0)
+  const counts = new Map<string, number>()
+  for (const event of events) {
+    counts.set(event.entrypoint, (counts.get(event.entrypoint) ?? 0) + 1)
+  }
+  const byEntrypoint = [...counts.entries()]
+    .map(([entrypoint, count]) => `${entrypoint}:${count}`)
+    .join(', ')
+
+  return `sqlite busy events=${events.length} retries=${retries.length} gaveUp=${gaveUp.length} totalWait=${formatDurationMs(totalWaitMs)} byWorker=[${byEntrypoint}]`
+}
+
 async function runTimedStep<T>(
   step: StepContext,
   name: string,
@@ -90,6 +109,7 @@ export async function analyzeAndFinalizeSteps(
   const allReviews: AnalyzedReview[] = []
   const allReviewers: AnalyzedReviewer[] = []
   const allReviewResponses: AnalyzedReviewResponse[] = []
+  const sqliteBusyEvents: SqliteBusyEvent[] = []
 
   for (let i = 0; i < organization.repositories.length; i++) {
     const repo = organization.repositories[i]
@@ -101,16 +121,21 @@ export async function analyzeAndFinalizeSteps(
 
         const orgSetting = organization.organizationSetting
         const prNumbers = filterPrNumbers?.get(repo.id)
-        return await runAnalyzeInWorker<AnalyzeResult>({
-          organizationId: orgId,
-          repositoryId: repo.id,
-          releaseDetectionMethod:
-            repo.releaseDetectionMethod ?? orgSetting.releaseDetectionMethod,
-          releaseDetectionKey:
-            repo.releaseDetectionKey ?? orgSetting.releaseDetectionKey,
-          excludedUsers: orgSetting.excludedUsers,
-          filterPrNumbers: prNumbers ? [...prNumbers] : undefined,
-        })
+        return await runAnalyzeInWorker<AnalyzeResult>(
+          {
+            organizationId: orgId,
+            repositoryId: repo.id,
+            releaseDetectionMethod:
+              repo.releaseDetectionMethod ?? orgSetting.releaseDetectionMethod,
+            releaseDetectionKey:
+              repo.releaseDetectionKey ?? orgSetting.releaseDetectionKey,
+            excludedUsers: orgSetting.excludedUsers,
+            filterPrNumbers: prNumbers ? [...prNumbers] : undefined,
+          },
+          {
+            onSqliteBusy: (event) => sqliteBusyEvents.push(event),
+          },
+        )
       })
     })
     allPulls.push(...result.pulls)
@@ -124,8 +149,7 @@ export async function analyzeAndFinalizeSteps(
     await step.run('upsert', async () => {
       await runTimedStep(step, 'upsert', async () => {
         step.progress(0, 0, 'Upserting to database...')
-        await runUpsertInWorker({
-          organizationId: orgId,
+        await upsertAnalyzedData(orgId, {
           pulls: allPulls,
           reviews: allReviews,
           reviewers: allReviewers,
@@ -164,11 +188,15 @@ export async function analyzeAndFinalizeSteps(
   await step.run('finalize', async () => {
     await runTimedStep(step, 'finalize', async () => {
       step.progress(0, 0, 'Finalizing...')
-      const tenantDb = getTenantDb(orgId)
-      await sql`PRAGMA wal_checkpoint(PASSIVE)`.execute(tenantDb)
       clearOrgCache(orgId)
+      await Promise.resolve()
     })
   })
 
+  const busySummary = summarizeBusyEvents(sqliteBusyEvents)
+  if (busySummary) {
+    step.log.warn(busySummary)
+  }
+
   return { pullCount: allPulls.length }
 }
diff --git a/app/services/jobs/upsert-worker.ts b/app/services/jobs/upsert-worker.ts
deleted file mode 100644
index bae3e307..00000000
--- a/app/services/jobs/upsert-worker.ts
+++ /dev/null
@@ -1,35 +0,0 @@
-/**
- * Worker thread for DB-heavy analyzed-data upsert.
- *
- * IMPORTANT: module.register() must be called before any ~/... imports.
- */
-if (import.meta.url.endsWith('.ts')) {
-  const { register } = await import('node:module')
-  register('./path-alias-hooks.mjs', import.meta.url)
-}
-
-import 'dotenv/config'
-import type { Selectable } from 'kysely'
-import { parentPort, workerData } from 'node:worker_threads'
-import type { TenantDB } from '~/app/services/tenant-db.server'
-import type { OrganizationId } from '~/app/types/organization'
-import type { AnalyzedReview, AnalyzedReviewer } from '~/batch/github/types'
-
-interface WorkerInput {
-  organizationId: string
-  pulls: Selectable<TenantDB.PullRequests>[]
-  reviews: AnalyzedReview[]
-  reviewers: AnalyzedReviewer[]
-}
-
-const input = workerData as WorkerInput
-
-const { upsertAnalyzedData } = await import('~/batch/db')
-
-await upsertAnalyzedData(input.organizationId as OrganizationId, {
-  pulls: input.pulls,
-  reviews: input.reviews,
-  reviewers: input.reviewers,
-})
-
-parentPort?.postMessage({ ok: true as const })
diff --git a/app/services/tenant-db.server.ts b/app/services/tenant-db.server.ts
index 54c71978..ee8a9173 100644
--- a/app/services/tenant-db.server.ts
+++ b/app/services/tenant-db.server.ts
@@ -18,6 +18,7 @@ export type { OrganizationId } from '~/app/types/organization'
 
 const debug = createDebug('app:tenant-db')
 const SQLITE_BUSY_TIMEOUT_MS = 5000
+const SQLITE_WAL_JOURNAL_SIZE_LIMIT_BYTES = 64 * 1024 * 1024
 
 const tenantDbCache = new Map<
   string,
@@ -42,6 +43,7 @@ function ensureTenantDb(organizationId: OrganizationId) {
   database.pragma('journal_mode = WAL')
   database.pragma(`busy_timeout = ${SQLITE_BUSY_TIMEOUT_MS}`)
   database.pragma('wal_autocheckpoint = 1000')
+  database.pragma(`journal_size_limit = ${SQLITE_WAL_JOURNAL_SIZE_LIMIT_BYTES}`)
 
   const kysely = new Kysely<TenantDB.DB>({
     dialect: new SqliteDialect({ database }),
diff --git a/batch/cli.ts b/batch/cli.ts
index 1072f577..2a4190c0 100644
--- a/batch/cli.ts
+++ b/batch/cli.ts
@@ -104,7 +104,7 @@ const backfill = command(
     },
     help: {
       description:
-        'Re-fetch PR metadata to fill missing fields in raw data. Run recalculate after this.',
+        'Re-fetch PR metadata to fill missing fields in raw data. Runs as a durable job. Run recalculate after this.',
     },
   },
   async (argv) => {
diff --git a/batch/commands/backfill.ts b/batch/commands/backfill.ts
index f40889f2..dae27f53 100644
--- a/batch/commands/backfill.ts
+++ b/batch/commands/backfill.ts
@@ -1,6 +1,5 @@
 import consola from 'consola'
-import invariant from 'tiny-invariant'
-import { backfillRepo } from '~/batch/github/backfill-repo'
+import { durably } from '~/app/services/durably.server'
 import { requireOrganization } from './helpers'
 import { shutdown } from './shutdown'
 
@@ -13,18 +12,34 @@ export async function backfillCommand(props: BackfillCommandProps) {
   const result = await requireOrganization(props.organizationId)
   if (!result) return
 
-  const { orgId, organization } = result
-  invariant(organization.integration, 'integration should related')
+  const { orgId } = result
 
   try {
-    for (const repository of organization.repositories) {
-      await backfillRepo(orgId, repository, organization.integration, {
-        files: props.files,
-      })
-    }
+    consola.info(
+      `Starting backfill for ${orgId}${props.files ? ' (files only)' : ''}...`,
+    )
 
-    consola.success('backfill completed. Run `recalculate` to apply changes.')
+    const { output } = await durably.jobs.backfill.triggerAndWait(
+      { organizationId: orgId, files: props.files ?? false },
+      {
+        concurrencyKey: `backfill:${orgId}`,
+        labels: { organizationId: orgId },
+        onProgress: (p) => {
+          if (p.message) consola.info(p.message)
+        },
+        onLog: (l) => {
+          if (l.level === 'error') consola.error(l.message)
+          else if (l.level === 'warn') consola.warn(l.message)
+          else consola.info(l.message)
+        },
+      },
+    )
+
+    consola.success(
+      `Backfill completed for ${output.repositoryCount} repositories. Run \`recalculate\` to apply changes.`,
+    )
   } finally {
+    await durably.stop()
     await shutdown()
   }
 }
diff --git a/batch/db/mutations.ts b/batch/db/mutations.ts
index 7e68a022..b3acd3e6 100644
--- a/batch/db/mutations.ts
+++ b/batch/db/mutations.ts
@@ -1,4 +1,5 @@
 import type { Insertable, Selectable } from 'kysely'
+import { setImmediate as yieldToEventLoop } from 'node:timers/promises'
 import { getTenantDb, type TenantDB } from '~/app/services/tenant-db.server'
 import type { OrganizationId } from '~/app/types/organization'
 import type { AnalyzedReview, AnalyzedReviewer } from '../github/types'
@@ -63,7 +64,7 @@ export function upsertPullRequestReview(
 export async function batchUpsertPullRequests(
   organizationId: OrganizationId,
   rows: Insertable<TenantDB.PullRequests>[],
-  chunkSize = 50,
+  chunkSize = 20,
 ) {
   if (rows.length === 0) return
   const tenantDb = getTenantDb(organizationId)
@@ -101,13 +102,15 @@ export async function batchUpsertPullRequests(
         })),
       )
       .execute()
+
+    await yieldToEventLoop()
   }
 }
 
 export async function batchUpsertPullRequestReviews(
   organizationId: OrganizationId,
   rows: Insertable<TenantDB.PullRequestReviews>[],
-  chunkSize = 100,
+  chunkSize = 50,
 ) {
   if (rows.length === 0) return
   const tenantDb = getTenantDb(organizationId)
@@ -126,6 +129,8 @@ export async function batchUpsertPullRequestReviews(
         })),
       )
       .execute()
+
+    await yieldToEventLoop()
   }
 }
 
@@ -170,16 +175,15 @@ export async function upsertPullRequestReviewers(
 export async function batchReplacePullRequestReviewers(
   organizationId: OrganizationId,
   rows: AnalyzedReviewer[],
-  chunkSize = 100,
+  chunkSize = 25,
 ) {
   if (rows.length === 0) return
 
   const tenantDb = getTenantDb(organizationId)
 
-  await tenantDb.transaction().execute(async (trx) => {
-    for (let i = 0; i < rows.length; i += chunkSize) {
-      const chunk = rows.slice(i, i + chunkSize)
-
+  for (let i = 0; i < rows.length; i += chunkSize) {
+    const chunk = rows.slice(i, i + chunkSize)
+    await tenantDb.transaction().execute(async (trx) => {
       for (const row of chunk) {
         await trx
           .deleteFrom('pullRequestReviewers')
@@ -208,8 +212,10 @@ export async function batchReplacePullRequestReviewers(
       if (values.length > 0) {
         await trx.insertInto('pullRequestReviewers').values(values).execute()
       }
-    }
-  })
+    })
+
+    await yieldToEventLoop()
+  }
 }
 
 /**
diff --git a/package.json b/package.json
index 9dcfbacf..89e672ec 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "scripts": {
     "build": "run-s build:react-router build:job build:workers build:db-scripts",
     "build:job": "esbuild --platform=node --format=esm ./batch/job-scheduler.ts --outdir=build --bundle --packages=external",
-    "build:workers": "esbuild --platform=node --format=esm ./app/services/jobs/analyze-worker.ts ./app/services/jobs/upsert-worker.ts --outdir=build/workers --bundle --packages=external",
+    "build:workers": "esbuild --platform=node --format=esm ./app/services/jobs/analyze-worker.ts --outdir=build/workers --bundle --packages=external",
     "build:db-scripts": "esbuild --platform=node --format=esm ./db/apply-tenant-migrations.ts --outdir=build/db --bundle --packages=external",
     "build:react-router": "react-router build",
     "dev": "react-router dev",