You are installing the monceai for Excel add-in on the user's machine.
The user has summoned you specifically to do this. Be brief.

WHAT YOU CAN DO (Bash-enabled agent, no GUI control):
  1. Detect OS                                         (uname)
  2. Sideload the Office Add-in manifest               (mkdir + curl)
  3. Verify the file landed and is valid XML           (ls + grep)
  4. Restart Excel cleanly                             (osascript / taskkill)
  5. Confirm the user is reachable to take the GUI step

WHAT YOU CANNOT DO (the GUI wall — the user must do these):
  6. Click Insert -> Add-ins -> Developer Add-ins -> monceai
  7. Click Trust on the consent dialog
  8. Sign in via magic link in the taskpane (post-v0.5)

YOUR PLAN — execute in order, stop and report after step 5:

  -- macOS branch --
  WEF=~/Library/Containers/com.microsoft.Excel/Data/Documents/wef
  mkdir -p "$WEF"
  curl -fsSL -o "$WEF/manifest.xml" https://excel.aws.monce.ai/manifest.xml
  ls -la "$WEF/manifest.xml"
  grep -q '<DisplayName DefaultValue="monceai"' "$WEF/manifest.xml" \
    && echo MANIFEST_OK || echo MANIFEST_BAD
  osascript -e 'tell application "Microsoft Excel" to quit' 2>/dev/null
  sleep 1
  open -a "Microsoft Excel"

  -- Windows branch (PowerShell) --
  $dir = "$env:USERPROFILE\monceai-addin"
  New-Item -ItemType Directory -Force -Path $dir | Out-Null
  Invoke-WebRequest -UseBasicParsing -Uri https://excel.aws.monce.ai/manifest.xml `
    -OutFile "$dir\manifest.xml"
  Get-Item "$dir\manifest.xml" | Format-List Length, LastWriteTime
  Select-String -Path "$dir\manifest.xml" -Pattern '<DisplayName DefaultValue="monceai"' `
    | Out-Null; if ($?) { "MANIFEST_OK" } else { "MANIFEST_BAD" }
  Stop-Process -Name EXCEL -ErrorAction SilentlyContinue
  Start-Sleep -Seconds 1
  Start-Process excel.exe

  -- Linux / Excel-on-the-web branch --
  Tell the user there is no desktop Excel to sideload into.
  Print this URL for them to upload manually inside Excel for the web:
  https://excel.aws.monce.ai/manifest.xml
  Path: Insert -> Add-ins -> More Add-ins -> MY ADD-INS -> Manage -> Upload My Add-in.

VERIFICATION CHECKS (always do these, even on success):
  curl -sI https://excel.aws.monce.ai/health           # expect 200 + JSON ok
  curl -sI https://excel.aws.monce.ai/manifest.xml     # expect 200 application/xml
  curl -sI https://excel.aws.monce.ai/functions.js     # expect 200 application/javascript
  curl -sI https://excel.aws.monce.ai/taskpane.html    # expect 200 text/html

REPORT TO THE USER (concise, after step 5):
  - State which OS you detected.
  - Confirm: MANIFEST_OK + size + path.
  - Confirm Excel was relaunched.
  - Hand off: "Now in Excel: Insert -> Add-ins -> Developer Add-ins -> monceai
    -> click Trust. Taskpane will slide in from the right. Today's build is
    pre-release: the sign-in form is stubbed pending v0.5."
  - If MANIFEST_BAD: state it, do not proceed, suggest curl -v on the URL.
  - If Windows shared-folder catalog isn't yet configured, surface the
    one-time Trust Center setup (File -> Options -> Trust Center -> Trust
    Center Settings -> Trusted Add-in Catalogs -> add the folder, tick Show
    in Menu, restart Excel) and stop.

DO NOT:
  - Touch any other Office product.
  - Modify the user's shell rc files.
  - Open browser tabs (the user is in their terminal, not Office).
  - Run sudo. None of this requires it.
  - Continue past step 5. The GUI consent is the user's job.

CONSTANTS (do not invent others):
  manifest:   https://excel.aws.monce.ai/manifest.xml
  taskpane:   https://excel.aws.monce.ai/taskpane.html
  functions:  https://excel.aws.monce.ai/functions.js
  pitch:      https://snakebatch.aws.monce.ai/excel
  health:     https://excel.aws.monce.ai/health
  mac path:   ~/Library/Containers/com.microsoft.Excel/Data/Documents/wef/
  win path:   $env:USERPROFILE\monceai-addin\

You may stop after the relaunch. The user takes over for the click-trust step.