diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index d9b6f58..75dbec9 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -4,6 +4,9 @@ on:
   push:
   pull_request:
 
+permissions:
+  contents: read
+
 jobs:
   package:
     name: Package validation
@@ -11,12 +14,35 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v7
 
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v7
         with:
           python-version: "3.11"
 
       - name: Validate package
         run: python scripts/validate-package.py
+
+  posix-installers:
+    name: POSIX installers
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+
+      - name: Test install and uninstall
+        run: sh scripts/test-installers.sh
+
+  powershell-installers:
+    name: Windows PowerShell installers
+    runs-on: windows-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+
+      - name: Test install and uninstall
+        shell: powershell
+        run: .\scripts\test-installers.ps1
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a18a126..93b6774 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,8 @@
 
 - Documented global default activation after install.
 - Added `CAVEMAN_OPENCODE_DEFAULT_LEVEL` install-time override for `lite`, `full`, `ultra`, `wenyan`, `wenyan-lite`, and `wenyan-ultra`.
+- Accepted trailing commas in existing OpenCode configuration without changing comma-like text inside JSON strings.
+- Added functional install/uninstall tests for POSIX and Windows PowerShell environments.
 
 ## 0.2.0
 
diff --git a/install-opencode.ps1 b/install-opencode.ps1
index 8ca9cd4..f63c5b0 100644
--- a/install-opencode.ps1
+++ b/install-opencode.ps1
@@ -38,6 +38,60 @@ function Ensure-Property($Object, [string]$Name, $Value) {
   }
 }
 
+function Remove-JsonTrailingCommas([string]$Content) {
+  $result = [System.Text.StringBuilder]::new($Content.Length)
+  $inString = $false
+  $escaped = $false
+
+  for ($index = 0; $index -lt $Content.Length; $index++) {
+    $character = $Content[$index]
+
+    if ($inString) {
+      [void]$result.Append($character)
+      if ($escaped) {
+        $escaped = $false
+      } elseif ($character -eq '\') {
+        $escaped = $true
+      } elseif ($character -eq '"') {
+        $inString = $false
+      }
+      continue
+    }
+
+    if ($character -eq '"') {
+      $inString = $true
+      [void]$result.Append($character)
+      continue
+    }
+
+    if ($character -eq ',') {
+      $next = $index + 1
+      while ($next -lt $Content.Length -and [char]::IsWhiteSpace($Content[$next])) {
+        $next++
+      }
+      if ($next -lt $Content.Length -and ($Content[$next] -eq '}' -or $Content[$next] -eq ']')) {
+        continue
+      }
+    }
+
+    [void]$result.Append($character)
+  }
+
+  return $result.ToString()
+}
+
+function ConvertFrom-OpenCodeJson([string]$Content) {
+  try {
+    return $Content | ConvertFrom-Json
+  } catch {
+    $normalized = Remove-JsonTrailingCommas $Content
+    if ($normalized -eq $Content) {
+      throw
+    }
+    return $normalized | ConvertFrom-Json
+  }
+}
+
 if (-not (Test-Path -LiteralPath (Join-Path $sourceOpenCode "AGENTS.md"))) {
   $archiveUrl = $env:CAVEMAN_OPENCODE_ARCHIVE_URL
   if ([string]::IsNullOrWhiteSpace($archiveUrl)) {
@@ -81,7 +135,8 @@ $agentsText = $agentsText -replace "Default mode: full\.", "Default mode: $defau
 $agentsText | Set-Content -LiteralPath $agentsFile -Encoding UTF8
 
 if (Test-Path -LiteralPath $configFile) {
-  $config = Get-Content -LiteralPath $configFile -Raw -Encoding UTF8 | ConvertFrom-Json
+  $content = Get-Content -LiteralPath $configFile -Raw -Encoding UTF8
+  $config = ConvertFrom-OpenCodeJson $content
 } else {
   $config = [pscustomobject]@{}
 }
diff --git a/install-opencode.sh b/install-opencode.sh
index c960b82..55aa275 100755
--- a/install-opencode.sh
+++ b/install-opencode.sh
@@ -74,8 +74,63 @@ const [configFile, agentsFile] = process.argv.slice(2)
 const skills = ["caveman", "caveman-commit", "caveman-review", "caveman-help", "caveman-compress"]
 let config = {}
 
+function stripTrailingCommas(content) {
+  let result = ""
+  let inString = false
+  let escaped = false
+
+  for (let index = 0; index < content.length; index += 1) {
+    const character = content[index]
+
+    if (inString) {
+      result += character
+      if (escaped) {
+        escaped = false
+      } else if (character === "\\") {
+        escaped = true
+      } else if (character === '"') {
+        inString = false
+      }
+      continue
+    }
+
+    if (character === '"') {
+      inString = true
+      result += character
+      continue
+    }
+
+    if (character === ",") {
+      let next = index + 1
+      while (next < content.length && /\s/.test(content[next])) {
+        next += 1
+      }
+      if (content[next] === "}" || content[next] === "]") {
+        continue
+      }
+    }
+
+    result += character
+  }
+
+  return result
+}
+
+function parseConfig(content) {
+  try {
+    return JSON.parse(content)
+  } catch (error) {
+    const normalized = stripTrailingCommas(content)
+    if (normalized === content) {
+      throw error
+    }
+    return JSON.parse(normalized)
+  }
+}
+
 if (fs.existsSync(configFile)) {
-  config = JSON.parse(fs.readFileSync(configFile, "utf8"))
+  const content = fs.readFileSync(configFile, "utf8")
+  config = parseConfig(content)
 }
 
 config.instructions = Array.isArray(config.instructions) ? config.instructions : []
diff --git a/scripts/test-installers.ps1 b/scripts/test-installers.ps1
new file mode 100644
index 0000000..d4786a0
--- /dev/null
+++ b/scripts/test-installers.ps1
@@ -0,0 +1,80 @@
+$ErrorActionPreference = "Stop"
+
+function Assert-True([bool]$Condition, [string]$Message) {
+  if (-not $Condition) {
+    throw "Assertion failed: $Message"
+  }
+}
+
+$repo = Split-Path -Parent $PSScriptRoot
+$testRoot = Join-Path ([System.IO.Path]::GetTempPath()) ("caveman-opencode-test-" + [guid]::NewGuid().ToString("N"))
+$originalUserProfile = $env:USERPROFILE
+$originalDefaultLevel = $env:CAVEMAN_OPENCODE_DEFAULT_LEVEL
+
+try {
+  $env:USERPROFILE = $testRoot
+  $env:CAVEMAN_OPENCODE_DEFAULT_LEVEL = "ultra"
+
+  $configDir = Join-Path $testRoot ".config\opencode"
+  $configFile = Join-Path $configDir "opencode.json"
+  $agentsFile = Join-Path $configDir "AGENTS.caveman.md"
+  New-Item -ItemType Directory -Force -Path $configDir | Out-Null
+
+  @'
+{
+  "instructions": [
+    "keep.md",
+  ],
+  "custom": "literal,}",
+  "nested": {
+    "value": "literal,]",
+  },
+  "permission": {
+    "skill": {
+      "existing": "allow",
+    },
+  },
+}
+'@ | Set-Content -LiteralPath $configFile -Encoding UTF8
+
+  & (Join-Path $repo "install-opencode.ps1")
+
+  $config = Get-Content -LiteralPath $configFile -Raw -Encoding UTF8 | ConvertFrom-Json
+  $skills = @("caveman", "caveman-commit", "caveman-review", "caveman-help", "caveman-compress")
+
+  Assert-True (@($config.instructions).Count -eq 2) "installer should preserve and append instructions"
+  Assert-True (@($config.instructions) -contains "keep.md") "existing instruction should remain"
+  Assert-True (@($config.instructions) -contains $agentsFile) "Caveman instruction should be added"
+  Assert-True ($config.custom -eq "literal,}") "comma before a brace inside a string should remain"
+  Assert-True ($config.nested.value -eq "literal,]") "comma before a bracket inside a string should remain"
+  Assert-True ($config.permission.skill.existing -eq "allow") "existing skill permission should remain"
+  foreach ($skill in $skills) {
+    Assert-True ($config.permission.skill.$skill -eq "allow") "$skill should be allowed"
+  }
+  Assert-True ((Get-Content -LiteralPath $agentsFile -Raw -Encoding UTF8) -match "(?m)^Default mode: ultra\.") "default intensity should be applied"
+
+  & (Join-Path $repo "uninstall-opencode.ps1")
+
+  $config = Get-Content -LiteralPath $configFile -Raw -Encoding UTF8 | ConvertFrom-Json
+  Assert-True (@($config.instructions).Count -eq 1) "uninstaller should remove only the Caveman instruction"
+  Assert-True (@($config.instructions) -contains "keep.md") "existing instruction should survive uninstall"
+  Assert-True ($config.custom -eq "literal,}") "custom string should survive uninstall"
+  Assert-True ($config.nested.value -eq "literal,]") "nested string should survive uninstall"
+  Assert-True ($config.permission.skill.existing -eq "allow") "existing permission should survive uninstall"
+  foreach ($skill in $skills) {
+    Assert-True ($config.permission.skill.PSObject.Properties.Name -notcontains $skill) "$skill permission should be removed"
+  }
+  Assert-True (-not (Test-Path -LiteralPath $agentsFile)) "Caveman instruction file should be removed"
+
+  Write-Host "PowerShell installer tests passed."
+} finally {
+  $env:USERPROFILE = $originalUserProfile
+  if ($null -eq $originalDefaultLevel) {
+    Remove-Item Env:CAVEMAN_OPENCODE_DEFAULT_LEVEL -ErrorAction SilentlyContinue
+  } else {
+    $env:CAVEMAN_OPENCODE_DEFAULT_LEVEL = $originalDefaultLevel
+  }
+  if (Test-Path -LiteralPath $testRoot) {
+    Remove-Item -Recurse -Force -LiteralPath $testRoot
+  }
+}
diff --git a/scripts/test-installers.sh b/scripts/test-installers.sh
new file mode 100755
index 0000000..f72ad6b
--- /dev/null
+++ b/scripts/test-installers.sh
@@ -0,0 +1,81 @@
+#!/usr/bin/env sh
+set -eu
+
+repo=$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)
+test_root=$(mktemp -d "${TMPDIR:-/tmp}/caveman-opencode-test.XXXXXX")
+config_home="$test_root/config"
+config_dir="$config_home/opencode"
+config_file="$config_dir/opencode.json"
+agents_file="$config_dir/AGENTS.caveman.md"
+
+cleanup() {
+  rm -rf "$test_root"
+}
+trap cleanup EXIT
+
+mkdir -p "$config_dir"
+
+node - "$config_file" <<'NODE'
+const fs = require("fs")
+
+const [configFile] = process.argv.slice(2)
+fs.writeFileSync(
+  configFile,
+  `{
+  "instructions": [
+    "keep.md",
+  ],
+  "custom": "literal,}",
+  "nested": {
+    "value": "literal,]",
+  },
+  "permission": {
+    "skill": {
+      "existing": "allow",
+    },
+  },
+}
+`,
+)
+NODE
+
+CAVEMAN_OPENCODE_DEFAULT_LEVEL=ultra XDG_CONFIG_HOME="$config_home" sh "$repo/install-opencode.sh"
+
+node - "$config_file" "$agents_file" <<'NODE'
+const assert = require("assert").strict
+const fs = require("fs")
+
+const [configFile, agentsFile] = process.argv.slice(2)
+const config = JSON.parse(fs.readFileSync(configFile, "utf8"))
+const skills = ["caveman", "caveman-commit", "caveman-review", "caveman-help", "caveman-compress"]
+
+assert.deepEqual(config.instructions, ["keep.md", agentsFile])
+assert.equal(config.custom, "literal,}")
+assert.equal(config.nested.value, "literal,]")
+assert.equal(config.permission.skill.existing, "allow")
+for (const skill of skills) {
+  assert.equal(config.permission.skill[skill], "allow")
+}
+assert.match(fs.readFileSync(agentsFile, "utf8"), /^Default mode: ultra\./m)
+NODE
+
+XDG_CONFIG_HOME="$config_home" sh "$repo/uninstall-opencode.sh"
+
+node - "$config_file" "$agents_file" <<'NODE'
+const assert = require("assert").strict
+const fs = require("fs")
+
+const [configFile, agentsFile] = process.argv.slice(2)
+const config = JSON.parse(fs.readFileSync(configFile, "utf8"))
+const skills = ["caveman", "caveman-commit", "caveman-review", "caveman-help", "caveman-compress"]
+
+assert.deepEqual(config.instructions, ["keep.md"])
+assert.equal(config.custom, "literal,}")
+assert.equal(config.nested.value, "literal,]")
+assert.equal(config.permission.skill.existing, "allow")
+for (const skill of skills) {
+  assert.equal(config.permission.skill[skill], undefined)
+}
+assert.equal(fs.existsSync(agentsFile), false)
+console.log("POSIX installer tests passed.")
+NODE
diff --git a/uninstall-opencode.ps1 b/uninstall-opencode.ps1
index 7de4a47..acff446 100644
--- a/uninstall-opencode.ps1
+++ b/uninstall-opencode.ps1
@@ -14,6 +14,60 @@ $skills = @(
   "caveman-compress"
 )
 
+function Remove-JsonTrailingCommas([string]$Content) {
+  $result = [System.Text.StringBuilder]::new($Content.Length)
+  $inString = $false
+  $escaped = $false
+
+  for ($index = 0; $index -lt $Content.Length; $index++) {
+    $character = $Content[$index]
+
+    if ($inString) {
+      [void]$result.Append($character)
+      if ($escaped) {
+        $escaped = $false
+      } elseif ($character -eq '\') {
+        $escaped = $true
+      } elseif ($character -eq '"') {
+        $inString = $false
+      }
+      continue
+    }
+
+    if ($character -eq '"') {
+      $inString = $true
+      [void]$result.Append($character)
+      continue
+    }
+
+    if ($character -eq ',') {
+      $next = $index + 1
+      while ($next -lt $Content.Length -and [char]::IsWhiteSpace($Content[$next])) {
+        $next++
+      }
+      if ($next -lt $Content.Length -and ($Content[$next] -eq '}' -or $Content[$next] -eq ']')) {
+        continue
+      }
+    }
+
+    [void]$result.Append($character)
+  }
+
+  return $result.ToString()
+}
+
+function ConvertFrom-OpenCodeJson([string]$Content) {
+  try {
+    return $Content | ConvertFrom-Json
+  } catch {
+    $normalized = Remove-JsonTrailingCommas $Content
+    if ($normalized -eq $Content) {
+      throw
+    }
+    return $normalized | ConvertFrom-Json
+  }
+}
+
 foreach ($skill in $skills) {
   $skillPath = Join-Path $skillsDir $skill
   if (Test-Path -LiteralPath $skillPath) {
@@ -33,7 +87,8 @@ if (Test-Path -LiteralPath $agentsFile) {
 }
 
 if (Test-Path -LiteralPath $configFile) {
-  $config = Get-Content -LiteralPath $configFile -Raw -Encoding UTF8 | ConvertFrom-Json
+  $content = Get-Content -LiteralPath $configFile -Raw -Encoding UTF8
+  $config = ConvertFrom-OpenCodeJson $content
   if ($config.PSObject.Properties.Name -contains "instructions") {
     $config.instructions = @(@($config.instructions) | Where-Object { $_ -ne $agentsFile })
   }
diff --git a/uninstall-opencode.sh b/uninstall-opencode.sh
index 4b09d85..97e7f29 100755
--- a/uninstall-opencode.sh
+++ b/uninstall-opencode.sh
@@ -24,7 +24,63 @@ const fs = require("fs")
 
 const [configFile, agentsFile] = process.argv.slice(2)
 const skills = ["caveman", "caveman-commit", "caveman-review", "caveman-help", "caveman-compress"]
-const config = JSON.parse(fs.readFileSync(configFile, "utf8"))
+
+function stripTrailingCommas(content) {
+  let result = ""
+  let inString = false
+  let escaped = false
+
+  for (let index = 0; index < content.length; index += 1) {
+    const character = content[index]
+
+    if (inString) {
+      result += character
+      if (escaped) {
+        escaped = false
+      } else if (character === "\\") {
+        escaped = true
+      } else if (character === '"') {
+        inString = false
+      }
+      continue
+    }
+
+    if (character === '"') {
+      inString = true
+      result += character
+      continue
+    }
+
+    if (character === ",") {
+      let next = index + 1
+      while (next < content.length && /\s/.test(content[next])) {
+        next += 1
+      }
+      if (content[next] === "}" || content[next] === "]") {
+        continue
+      }
+    }
+
+    result += character
+  }
+
+  return result
+}
+
+function parseConfig(content) {
+  try {
+    return JSON.parse(content)
+  } catch (error) {
+    const normalized = stripTrailingCommas(content)
+    if (normalized === content) {
+      throw error
+    }
+    return JSON.parse(normalized)
+  }
+}
+
+const content = fs.readFileSync(configFile, "utf8")
+const config = parseConfig(content)
 
 if (Array.isArray(config.instructions)) {
   config.instructions = config.instructions.filter((item) => item !== agentsFile)