diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7410b0cdf..cdec8ac65 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -347,9 +347,9 @@ jobs:
     needs: changes
     if: needs.changes.outputs.docs_only != 'true'
     runs-on: windows-latest
-    # Windows unit jobs are advisory and package-scoped. The 20-minute budget
-    # gives each matrix child room for Windows runner setup and install overhead
-    # while still surfacing the package that timed out.
+    # Windows unit jobs are advisory, package-scoped or shard-scoped. The
+    # 20-minute budget applies per matrix child; opencode has three parallel
+    # shards, so a full stall can consume up to three Windows runner slots.
     timeout-minutes: 20
     continue-on-error: true
     strategy:
@@ -357,12 +357,88 @@ jobs:
       matrix:
         include:
           - package: app
+            uses_turbo: true
             command: bun turbo test:ci --filter=@opencode-ai/app
             report_path: packages/app/.artifacts/unit/junit.xml
-          - package: opencode
-            command: bun turbo test:ci --filter=opencode
-            report_path: packages/opencode/.artifacts/unit/junit.xml
+          # The opencode-* package values below are synthetic shard names for
+          # readable advisory checks and matrix keys, not package.json names.
+          # Direct bun test keeps opencode's test:ci timeout while allowing
+          # shard-local paths and reporter output. Shards are balanced by
+          # observed runtime, not directory count.
+          # Session also carries plugin, permission, util, skill, and root
+          # tests to keep the Windows shard runtimes close.
+          - package: opencode-session
+            uses_turbo: false
+            command: >-
+              cd packages/opencode && bun test
+              --timeout 30000
+              --reporter=junit
+              --reporter-outfile=.artifacts/unit/junit-windows-session.xml
+              test/session
+              test/plugin
+              test/permission
+              test/util
+              test/skill
+              test/index-runtime-namespace.test.ts
+              test/npm.test.ts
+              test/permission-task.test.ts
+            report_path: packages/opencode/.artifacts/unit/junit-windows-session.xml
+          # Config and project cover configuration, project discovery, file,
+          # and GitHub workflow tests.
+          - package: opencode-config-project
+            uses_turbo: false
+            command: >-
+              cd packages/opencode && bun test
+              --timeout 30000
+              --reporter=junit
+              --reporter-outfile=.artifacts/unit/junit-windows-config-project.xml
+              test/config
+              test/project
+              test/file
+              test/github
+            report_path: packages/opencode/.artifacts/unit/junit-windows-config-project.xml
+          # Server tools carries many smaller and faster directories, which is
+          # why it has more entries than the other two opencode shards.
+          - package: opencode-server-tools
+            uses_turbo: false
+            command: >-
+              cd packages/opencode && bun test
+              --timeout 30000
+              --reporter=junit
+              --reporter-outfile=.artifacts/unit/junit-windows-server-tools.xml
+              test/server
+              test/snapshot
+              test/tool
+              test/mcp
+              test/question
+              test/effect
+              test/agent
+              test/git
+              test/storage
+              test/provider
+              test/pty
+              test/share
+              test/script
+              test/memory
+              test/lsp
+              test/fixture
+              test/acp
+              test/bus
+              test/cli
+              test/global
+              test/format
+              test/account
+              test/sync
+              test/filesystem
+              test/patch
+              test/shell
+              test/control-plane
+              test/ide
+              test/installation
+              test/auth
+            report_path: packages/opencode/.artifacts/unit/junit-windows-server-tools.xml
           - package: desktop
+            uses_turbo: true
             command: bun turbo test:ci --filter=@opencode-ai/desktop-electron
             report_path: packages/desktop-electron/.artifacts/unit/junit.xml
     permissions:
@@ -396,10 +472,10 @@ jobs:
             bun-${{ runner.os }}-
 
       - uses: actions/cache@27d5ce7f107fe9357f9df03efb73ab90386fccae # actions/cache@v5
+        if: matrix.uses_turbo
         with:
           path: .turbo/cache
-          # Keep Turbo caches package-scoped because each matrix child runs a
-          # different test filter; restore keys reuse only that package's cache.
+          # Only app and desktop invoke Turbo in this Windows matrix.
           key: turbo-${{ runner.os }}-unit-windows-${{ matrix.package }}-${{ hashFiles('turbo.json', '**/package.json', 'bun.lock') }}-${{ github.sha }}
           restore-keys: |
             turbo-${{ runner.os }}-unit-windows-${{ matrix.package }}-${{ hashFiles('turbo.json', '**/package.json', 'bun.lock') }}-
@@ -407,6 +483,10 @@ jobs:
 
       - run: bun install --frozen-lockfile
 
+      - name: Prepare unit artifact directory
+        if: matrix.uses_turbo == false
+        run: mkdir -p "$(dirname "${{ matrix.report_path }}")"
+
       - name: unit
         id: unit
         continue-on-error: true
diff --git a/packages/opencode/test/github/ci-workflow.test.ts b/packages/opencode/test/github/ci-workflow.test.ts
index 2e3abbaf1..e8e0bab45 100644
--- a/packages/opencode/test/github/ci-workflow.test.ts
+++ b/packages/opencode/test/github/ci-workflow.test.ts
@@ -1,9 +1,11 @@
 import { describe, expect, test } from "bun:test"
+import { existsSync, readdirSync, statSync } from "node:fs"
 import path from "node:path"
 import { parseWorkflow, readWorkflow } from "./workflow-parser"
 
 const repoRoot = path.join(import.meta.dir, "../../../..")
 const workflowPath = path.join(repoRoot, ".github", "workflows", "ci.yml")
+const opencodeTestRoot = path.join(repoRoot, "packages", "opencode", "test")
 
 const pinned = {
   checkout: "actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd",
@@ -19,7 +21,7 @@ const windowsUnitJobName = "unit-windows"
 
 // Suffixes drive readable job and artifact names; commands use package.json names verbatim.
 // `opencode` is intentionally unscoped because that is its actual package name.
-const unitPackages = [
+const linuxUnitPackages = [
   {
     suffix: "app",
     command: "bun turbo test:ci --filter=@opencode-ai/app",
@@ -37,14 +39,57 @@ const unitPackages = [
   },
 ] as const
 
-const linuxUnitJobs = unitPackages.map((pkg) => ({
+const windowsOpencodeShards = [
+  // Intentional dual source with ci.yml: this pins the exact shard command
+  // contract while the coverage test expands these paths to catch workflow
+  // drift and missing opencode tests. Update ci.yml and this list together.
+  {
+    suffix: "opencode-session",
+    usesTurbo: false,
+    command:
+      "cd packages/opencode && bun test --timeout 30000 --reporter=junit --reporter-outfile=.artifacts/unit/junit-windows-session.xml test/session test/plugin test/permission test/util test/skill test/index-runtime-namespace.test.ts test/npm.test.ts test/permission-task.test.ts",
+    reportPath: "packages/opencode/.artifacts/unit/junit-windows-session.xml",
+  },
+  {
+    suffix: "opencode-config-project",
+    usesTurbo: false,
+    command:
+      "cd packages/opencode && bun test --timeout 30000 --reporter=junit --reporter-outfile=.artifacts/unit/junit-windows-config-project.xml test/config test/project test/file test/github",
+    reportPath: "packages/opencode/.artifacts/unit/junit-windows-config-project.xml",
+  },
+  {
+    suffix: "opencode-server-tools",
+    usesTurbo: false,
+    command:
+      "cd packages/opencode && bun test --timeout 30000 --reporter=junit --reporter-outfile=.artifacts/unit/junit-windows-server-tools.xml test/server test/snapshot test/tool test/mcp test/question test/effect test/agent test/git test/storage test/provider test/pty test/share test/script test/memory test/lsp test/fixture test/acp test/bus test/cli test/global test/format test/account test/sync test/filesystem test/patch test/shell test/control-plane test/ide test/installation test/auth",
+    reportPath: "packages/opencode/.artifacts/unit/junit-windows-server-tools.xml",
+  },
+] as const
+
+const windowsUnitPackages = [
+  {
+    suffix: "app",
+    usesTurbo: true,
+    command: "bun turbo test:ci --filter=@opencode-ai/app",
+    reportPath: "packages/app/.artifacts/unit/junit.xml",
+  },
+  ...windowsOpencodeShards,
+  {
+    suffix: "desktop",
+    usesTurbo: true,
+    command: "bun turbo test:ci --filter=@opencode-ai/desktop-electron",
+    reportPath: "packages/desktop-electron/.artifacts/unit/junit.xml",
+  },
+] as const
+
+const linuxUnitJobs = linuxUnitPackages.map((pkg) => ({
   ...pkg,
   jobName: `unit-${pkg.suffix}`,
   checkName: `unit results (${pkg.suffix})`,
   artifactName: `unit-${pkg.suffix}-${runAttempt}`,
 }))
 
-const windowsUnitJobs = unitPackages.map((pkg) => ({
+const windowsUnitJobs = windowsUnitPackages.map((pkg) => ({
   ...pkg,
   jobName: `unit-windows-${pkg.suffix}`,
   artifactName: `unit-windows-${pkg.suffix}-${runAttempt}`,
@@ -63,6 +108,47 @@ function stepByName(job: string, name: string) {
   return steps(job).find((step) => step.name === name)
 }
 
+function toPosix(relativePath: string) {
+  return relativePath.split(path.sep).join("/")
+}
+
+function isTestFile(filePath: string) {
+  return /\.(test|spec)\.(ts|tsx|js|mjs|cjs)$/.test(filePath)
+}
+
+function listOpencodeTestFiles(dir = opencodeTestRoot): string[] {
+  return readdirSync(dir, { withFileTypes: true }).flatMap((entry) => {
+    const fullPath = path.join(dir, entry.name)
+    if (entry.isDirectory()) return listOpencodeTestFiles(fullPath)
+    if (!entry.isFile() || !isTestFile(entry.name)) return []
+
+    return [`test/${toPosix(path.relative(opencodeTestRoot, fullPath))}`]
+  })
+}
+
+function expandOpencodeTestPath(testPath: string): string[] {
+  const fullPath = path.join(repoRoot, "packages", "opencode", testPath)
+  if (!existsSync(fullPath)) {
+    throw new Error(`Windows opencode shard path does not exist: ${testPath}`)
+  }
+  if (statSync(fullPath).isDirectory()) {
+    return listOpencodeTestFiles(fullPath)
+  }
+  return [testPath]
+}
+
+function testPathArgs(command: string) {
+  const testArgs = command.split(" bun test ")[1]
+  if (!testArgs) {
+    throw new Error(`Windows opencode shard command does not invoke bun test: ${command}`)
+  }
+  return testArgs.split(/\s+/).filter((arg) => arg.startsWith("test/"))
+}
+
+function isWindowsOpencodeShard(item: Record<string, unknown>): item is { command: string; package: string } {
+  return item.uses_turbo === false && typeof item.package === "string" && typeof item.command === "string"
+}
+
 describe("ci workflow", () => {
   test("pins third-party actions and disables checkout credential persistence", () => {
     const workflow = readWorkflow(workflowPath)
@@ -148,10 +234,9 @@ describe("ci workflow", () => {
     }
   })
 
-  test("splits Windows unit signals by package without publishing advisory check runs", () => {
+  test("keeps Windows unit package and shard signals advisory", () => {
     const parsed = parseWorkflow(workflowPath)
     const job = parsed.jobs?.[windowsUnitJobName]
-    const matrixIncludes = job?.strategy?.matrix?.include ?? []
 
     expect(job?.name).toBe("unit-windows-${{ matrix.package }}")
     expect(job?.needs).toBe("changes")
@@ -162,6 +247,10 @@ describe("ci workflow", () => {
     expect(job?.strategy?.["fail-fast"]).toBe(false)
     expect(job?.permissions).toEqual({ contents: "read" })
     expect(job?.defaults?.run?.shell).toBe("bash")
+    expect(stepByName(windowsUnitJobName, "Prepare unit artifact directory")?.run).toBe(
+      'mkdir -p "$(dirname "${{ matrix.report_path }}")"',
+    )
+    expect(stepByName(windowsUnitJobName, "Prepare unit artifact directory")?.if).toBe("matrix.uses_turbo == false")
     expect(stepByName(windowsUnitJobName, "unit")?.id).toBe("unit")
     expect(stepByName(windowsUnitJobName, "unit")?.["continue-on-error"]).toBe(true)
     expect(stepByName(windowsUnitJobName, "unit")?.run).toContain("${{ matrix.command }}")
@@ -175,7 +264,8 @@ describe("ci workflow", () => {
     )
     expect(stepByName(windowsUnitJobName, "Upload unit artifacts")?.with?.path).toBe("${{ matrix.report_path }}")
 
-    const turboCacheStep = steps(windowsUnitJobName).filter((step) => step.uses?.startsWith("actions/cache@"))[1]
+    const turboCacheStep = steps(windowsUnitJobName).find((step) => step.with?.path === ".turbo/cache")
+    expect(turboCacheStep?.if).toBe("matrix.uses_turbo")
     expect(turboCacheStep?.with?.key).toBe(
       "turbo-${{ runner.os }}-unit-windows-${{ matrix.package }}-${{ hashFiles('turbo.json', '**/package.json', 'bun.lock') }}-${{ github.sha }}",
     )
@@ -183,21 +273,90 @@ describe("ci workflow", () => {
       "turbo-${{ runner.os }}-unit-windows-${{ matrix.package }}-${{ hashFiles('turbo.json', '**/package.json', 'bun.lock') }}-\n" +
         "turbo-${{ runner.os }}-unit-windows-${{ matrix.package }}-\n",
     )
+  })
+
+  test("defines Windows unit packages and opencode shards", () => {
+    const parsed = parseWorkflow(workflowPath)
+    const job = parsed.jobs?.[windowsUnitJobName]
+    const matrixIncludes = job?.strategy?.matrix?.include ?? []
 
     expect(matrixIncludes).toEqual(
-      windowsUnitJobs.map(({ jobName, command, reportPath }) => ({
+      windowsUnitJobs.map(({ jobName, usesTurbo, command, reportPath }) => ({
         package: jobName.replace("unit-windows-", ""),
+        uses_turbo: usesTurbo,
         command,
         report_path: reportPath,
       })),
     )
 
-    for (const { jobName, command, reportPath, artifactName } of windowsUnitJobs) {
+    for (const { jobName, artifactName } of windowsUnitJobs) {
       expect(parsed.jobs?.[jobName]).toBeUndefined()
       expect(artifactName).toBe(`unit-windows-${jobName.replace("unit-windows-", "")}-${runAttempt}`)
     }
   })
 
+  test("covers each opencode test file exactly once across Windows opencode shards", () => {
+    const parsed = parseWorkflow(workflowPath)
+    const matrixIncludes = parsed.jobs?.[windowsUnitJobName]?.strategy?.matrix?.include ?? []
+    const opencodeShards = matrixIncludes.filter(isWindowsOpencodeShard)
+    const allTestFiles = listOpencodeTestFiles().sort()
+    const allTestFilesSet = new Set(allTestFiles)
+    const coverage = new Map<string, string[]>()
+    const extra: string[] = []
+    const shardFileCounts = new Map<string, number>()
+
+    // This repeats names instead of deriving from windowsOpencodeShards so the
+    // coverage test pins the public advisory check names explicitly.
+    expect(opencodeShards.map((item) => item.package)).toEqual([
+      "opencode-session",
+      "opencode-config-project",
+      "opencode-server-tools",
+    ])
+
+    for (const item of opencodeShards) {
+      const testPaths = testPathArgs(item.command)
+      let fileCount = 0
+      for (const testPath of testPaths) {
+        const expanded = expandOpencodeTestPath(testPath)
+        fileCount += expanded.length
+        for (const file of expanded) {
+          if (!allTestFilesSet.has(file)) {
+            extra.push(file)
+            continue
+          }
+          coverage.set(file, [...(coverage.get(file) ?? []), item.package])
+        }
+      }
+      shardFileCounts.set(item.package, fileCount)
+    }
+
+    const missing = allTestFiles.filter((file) => !coverage.has(file))
+    const duplicates = [...coverage.entries()]
+      .filter(([, shardNames]) => shardNames.length > 1)
+      .map(([file, shardNames]) => ({ file, shards: shardNames }))
+
+    if (missing.length > 0 || extra.length > 0 || duplicates.length > 0) {
+      const shardNames = opencodeShards.map((item) => item.package)
+      const smallestShard = [...shardFileCounts.entries()].sort(([, left], [, right]) => left - right)[0]?.[0]
+      const details = [
+        "Windows opencode shard coverage drift.",
+        missing.length > 0 ? `Uncovered files: ${missing.join(", ")}` : undefined,
+        extra.length > 0 ? `Unknown shard paths: ${extra.sort().join(", ")}` : undefined,
+        duplicates.length > 0 ? `Duplicate coverage: ${JSON.stringify(duplicates)}` : undefined,
+        `Shard choices: ${shardNames.join(" | ")}`,
+        smallestShard ? `Suggested starting shard for uncovered files: ${smallestShard}` : undefined,
+      ].filter((line): line is string => typeof line === "string")
+
+      throw new Error(details.join("\n"))
+    }
+
+    expect({ duplicates, extra: extra.sort(), missing }).toEqual({
+      duplicates: [],
+      extra: [],
+      missing: [],
+    })
+  })
+
   test("keeps docs-only behavior and excludes Windows from the blocking aggregate", () => {
     const parsed = parseWorkflow(workflowPath)
     const check = parsed.jobs?.check
@@ -210,6 +369,9 @@ describe("ci workflow", () => {
     expect(needs).not.toContain("unit-windows-app")
     expect(needs).not.toContain("unit-windows-desktop")
     expect(needs).not.toContain("unit-windows-opencode")
+    expect(needs).not.toContain("unit-windows-opencode-session")
+    expect(needs).not.toContain("unit-windows-opencode-config-project")
+    expect(needs).not.toContain("unit-windows-opencode-server-tools")
     expect(validate?.env?.DOCS_ONLY).toBe("${{ needs.changes.outputs.docs_only }}")
     expect(validate?.env?.TYPECHECK_RESULT).toBe("${{ needs.typecheck.result }}")
     expect(validate?.env?.UNIT_APP_RESULT).toBe("${{ needs['unit-app'].result }}")