cherrypicking-pr-to-v3

name	cherrypicking-pr-to-v3
description	Backports (cherry-picks) a merged PR from main (v4) to the v3 branch of buildkite/agent, translating v4 code back to v3 conventions. Use when asked to backport, cherry-pick, or port a PR or commit to v3.

Cherry-picking a PR to v3

Since August 2026, main is the v4 codebase. Stable v3 releases come from the v3 branch. A change that needs to reach customers in v3 must first merge to main, then be backported as a second PR against v3 with the same changes translated back to v3 conventions.

Workflow

1. Identify the merged PR/commit on main to backport. Never cherry-pick the v4 merge commit (8aea45a, PR #3807) itself — it is the entire v4 delta.
2. Apply the change onto v3: with jj, jj duplicate <rev> -d v3 (then jj edit the duplicate to resolve conflicts); with git, branch off v3 and git cherry-pick -x --no-commit <sha>. Resolve conflicts by translating the code as described below. PRs in this repo merge as two-parent merge commits, and the change lives in the constituent commit(s), not the merge commit: jj duplicate of the merge commit produces an empty commit, and git cherry-pick refuses it without -m 1. Select the PR's constituent commit(s) instead.
3. Translate all v4-isms back to v3 (see checklist).
4. Raise the backport PR against v3. Keep the description concise: state that it is a backport of the original PR (with a link) and note any translation deviations. Do not duplicate the original PR's full description — reviewers can follow the link.
5. Do not touch the VERSION file unless a release is explicitly requested.

Translation checklist (v4 → v3)

1. Import paths

The module changed major version. Rewrite every import:

-"github.com/buildkite/agent/v4/api"
+"github.com/buildkite/agent/v3/api"

Also check string-valued package paths, not just imports: tracer names (otel.Tracer("github.com/buildkite/agent/...")), linker flags, generated protobuf go_package_prefix, doc links. Never change the v3 branch's go.mod module declaration.

2. urfave/cli: v3 → v1

main uses github.com/urfave/cli/v3; the v3 branch uses github.com/urfave/cli (v1). Flags and commands are pointers in cli v3 but values in cli v1, and env vars are declared differently:

// main (cli v3)
&cli.StringFlag{
    Name:    "note",
    Usage:   "A descriptive note to record why the agent is paused",
    Sources: cli.EnvVars("BUILDKITE_AGENT_PAUSE_NOTE"),
}

// v3 branch (cli v1)
cli.StringFlag{
    Name:   "note",
    Usage:  "A descriptive note to record why the agent is paused",
    EnvVar: "BUILDKITE_AGENT_PAUSE_NOTE",
}

main (cli v3)	v3 branch (cli v1)
import "github.com/urfave/cli/v3"	import "github.com/urfave/cli"
&cli.Command{...}	cli.Command{...}
[]*cli.Command	[]cli.Command
&cli.StringFlag{...} (and Bool/Int/etc.)	cli.StringFlag{...}
Sources: cli.EnvVars("X")	EnvVar: "X"
Commands: []*cli.Command{...} (subcommands)	Subcommands: []cli.Command{...}
StringSliceFlag{Value: []string{}}	StringSliceFlag{Value: &cli.StringSlice{}}
cli.Exit(...)	cli.NewExitError(...)
flag.Names()	flag.GetName()

3. Action signatures and context

cli v3 actions receive a context.Context; cli v1 actions do not:

// main (cli v3)
Action: func(ctx context.Context, c *cli.Command) error {
    ctx, cfg, l, _, done := setupLoggerAndConfig[Config](ctx, c)
    ...
}

// v3 branch (cli v1)
Action: func(c *cli.Context) error {
    ctx := context.Background()
    ctx, cfg, l, _, done := setupLoggerAndConfig[Config](ctx, c)
    ...
}

Named action functions translate the same way: func fooAction(ctx context.Context, c *cli.Command) error becomes func fooAction(c *cli.Context) error with ctx := context.Background() inside. Do not change v3's shared setup helpers to accept *cli.Command.

4. CLI accessors

main (cli v3)	v3 branch (cli v1)
c *cli.Command	c *cli.Context
c.Root().Writer / c.Root().ErrWriter	c.App.Writer / c.App.ErrWriter
c.Args().Len()	len(c.Args())
c.Args().Slice()	c.Args()
c.Args().Get(0)	c.Args()[0]
clicommand.SomeFlag.Value (slice flag, []string)	*clicommand.SomeFlag.Value (deref *cli.StringSlice)

5. Tests

cli v3 tests build a root *cli.Command, clone commands (Run mutates them), and call app.Run(t.Context(), args). v3 tests use the v1 harness:

app := cli.NewApp()
app.Commands = []cli.Command{SomeCommand}
err := app.Run(args)

Do not copy the cli v3 command-cloning workaround into v3 tests.

Behavioral differences — don't backport v4 breaks by accident

A conflict may signal a deliberate v4 behavior change, not just code drift. Preserve v3 behavior unless changing it is the explicit purpose of the backport:

• Tracing/metrics: v3 still has Datadog/OpenTracing and DogStatsD (TracingBackend, TracingServiceName); v4 is OpenTelemetry-only (OpenTelemetryTracing, TelemetryServiceName). Map config fields back.
• Cancellation flags: v3 has --cancel-grace-period and --signal-grace-period-seconds; v4 replaced them with --cancel-signal-timeout and --cancel-cleanup-timeout.
• Experiments: v4 promoted or removed several experiments (normalized artifact upload paths, resolve-commit-after-checkout, etc.). A v4 diff may lack an experiment guard because the behavior is unconditional there; the v3 backport may need to keep or add the guard.
• Hook ordering: v4 reverses post-hook order by default; v3 does not.
• Commit verification: v4 defaults to strict and only supports strict/off; v3 supports the older empty/warn/strict values.
• SSH host keys: v4 uses GIT_SSH_COMMAND with StrictHostKeyChecking=accept-new; v3 still uses ssh-keyscan and known_hosts.
• Removed in v4, still in v3: deprecated Docker integration, deprecated artifact flags (follow-symlinks), plugin env aliases, header-times streamer/API. If the v4 patch assumes these are gone, the v3 backport needs a v3-specific integration point.
• Output: v4 intentionally changed some output (e.g. meta-data get gained a trailing newline). Don't pull such compatibility breaks into v3.

Reference

• Changelog: https://buildkite.com/resources/changelog/382-buildkite-agent-v4-becomes-the-stable-release-on-1-september-2026/
• Notion: "Making agent changes in the run-up to v4" (buildkite Notion, page 3b3b8dbc2c8980b5a623e6e678da893b)
• The v4 merge to main: https://github.com/buildkite/agent/pull/3807