feat: add Checker and Shipper interfaces, update README, and implement tests

[kazeburo]

PR Type

Enhancement, Tests, Documentation

---

Description

• Add Checker and Shipper execution modes

• Genericize Runner[T] message handling

• Share flag parsing and configuration construction

• Document APIs and test all modes

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Diagram Walkthrough

flowchart LR
  CLI["CLI arguments"] 
  Parser["Shared flag parser"]
  Runner["Runner[T]"]
  Checker["Checker"]
  Shipper["Shipper"]
  Output["Exit code and output"]
  CLI -- "parse" --> Parser
  Parser -- "execute" --> Runner
  Parser -- "execute" --> Checker
  Parser -- "execute" --> Shipper
  Runner -- "return message and status" --> Output
  Checker -- "map checker status" --> Output
  Shipper -- "return OK after side effect" --> Output

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File Walkthrough

	Relevant files
Enhancement	flagrun.go Add generic runner, checker, and shipper APIs                        flagrun.go Make Runner generic through Runner[T]. Add Checker and Shipper interfaces with Check and Ship entry points. Centralize Flagrun setup and command-line argument parsing. Map checkers.Checker statuses to plugin exit codes and handle nil results. +110/-27
Tests	flagrun_check_test.go Test checker execution and status mapping                                flagrun_check_test.go Add table-driven tests for all checker statuses. Cover checker help, version, and public Check behavior. Verify checker messages and mapped exit codes. +112/-0  flagrun_go_test.go Update generic runner execution tests                                        flagrun_go_test.go Update runner tests for generic internalGo setup. Add coverage for runners returning arbitrary message types. Verify error messages are formatted into output strings. +54/-6    flagrun_shipper_test.go Test shipper execution and CLI handling                                    flagrun_shipper_test.go Add tests confirming shipper execution side effects. Cover help and version paths without invoking the shipper. Verify public Ship returns OK. +65/-0
Documentation	README.md Document runner checker and shipper usage                                README.md Document Runner[T], Checker, and Shipper interfaces. Add usage examples for Check and Ship. Clarify output behavior and shared options across entry points. +74/-5
Dependencies	go.mod Add Mackerel checker dependency                                                    go.mod Add github.com/mackerelio/checkers dependency. +1/-0

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[github-actions]

PR Reviewer Guide 🔍

(Review updated until commit 9217c3b)

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 PR contains tests

🔒 No security concerns identified

⚡ Recommended focus areas for review Missing import The new Checker example calls os.Exit but does not import os, so users cannot compile it as shown. The same omission exists in the new Shipper example. import ( "github.com/mackerelio/checkers" "github.com/monitoring-forge/flagrun" )

[github-actions]

Persistent review updated to latest commit 763d846

[github-actions]

Persistent review updated to latest commit a1efaf4

[github-actions]

Persistent review updated to latest commit d6d0b1e

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Persistent review updated to latest commit 9217c3b