Add --payload-file flag to kernel invoke

[rgarcia]

Summary

Add a --payload-file / -f flag to kernel invoke that allows reading the JSON payload from a file instead of passing it inline. This is useful for:

• Large payloads that are unwieldy on the command line
• Payloads with special characters that need escaping
• Scripting and automation workflows
• Piping data from other commands

Usage

# Read payload from a file
kernel invoke myapp action -f payload.json

# Read payload from stdin
cat payload.json | kernel invoke myapp action -f -

# Pipe from another command
echo '{"key": "value"}' | kernel invoke myapp action -f -

# Combine with other tools
jq '.data' response.json | kernel invoke myapp process -f -

Details

• The --payload and --payload-file flags are mutually exclusive (enforced by cobra)
• Supports - as a special filename to read from stdin
• Validates that the file contents are valid JSON before invoking
• Trims whitespace from file contents

Test plan

• go build ./... passes
• go test ./... passes
• Help output shows new flag correctly
• Manual test: kernel invoke app action -f payload.json
• Manual test: echo '{}' | kernel invoke app action -f -
• Manual test: verify --payload and --payload-file cannot be used together

---

Note

Adds file/stdin-based payload input to kernel invoke with JSON validation and updates docs.

• Introduces --payload-file, -f flag in invoke (mutually exclusive with --payload)
• New getPayload helper supports reading from file or - (stdin), trims whitespace, and validates JSON before invoking
• Wires payload into invocation params when provided; preserves existing sync/async behavior
• README updated with new flag in command reference and examples for file/stdin/pipe usage

^{Written by Cursor Bugbot for commit d7205d5. This will update automatically on new commits. Configure here.}

[cursor]

Misleading error message for stdin JSON validation failure

Low Severity

When reading from stdin using -f -, the JSON validation error message says "invalid JSON in payload file" which is incorrect for stdin input. The read error messages correctly differentiate between stdin and file cases (lines 243 and 249), but the JSON validation error message at line 258 is shared and uses the file-specific wording. Users piping data via stdin will see a confusing error referencing a "payload file" that doesn't exist.