Add typed JSON output to app function run - #8756

WHY are these changes introduced?

app function run --json streams unvalidated child output. A failed execution can print a result followed by another fatal document, and runner diagnostics are not structured side events.

WHAT is this pull request doing?

Capture and validate the native Function runner 7.x/9.x result before encoding it. Preserve native keys and payloads, text presentation, and Speedscope files. Completed Function failures emit one result and exit nonzero; setup and invalid-output failures use the shared fatal-error envelope. Keep target prompting independent from JSON and honor --no-input.

Normal output (excerpt):

Output
{"operations":[]}
Benchmark Results
Name: function.wasm
Linear Memory Usage: 64KB
Instructions: 1K

Matching JSON:

{
  "name": "function.wasm",
  "size": 1,
  "memory_usage": 64,
  "instructions": 1000,
  "logs": "",
  "input": {},
  "output": {"operations": []},
  "success": true
}

How to manually test your changes?

shopify app function run --path /path/to/function --input input.json
shopify app function run --path /path/to/function --input input.json --json
shopify app function run --path /path/to/function --input input.json --json --profile
shopify app function run --json-schema

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — added a major changeset for the existing JSON contract

Stack

1. Add typed JSON output to app function info #8755 — Function info
2. Add typed JSON output to app function run #8756 — Function run
3. Add typed JSON output to app function replay #8757 — Function replay