feat: add --repo-retries for helm repo and registry login commands (#2683)

* feat: add --repo-retries for retrying helm repo and registry login commands

Add a configurable retry mechanism for chart repository operations to
handle unstable networks (corporate proxies, slow internal registries).

Closes #1894

- New --repo-retries N flag and HELMFILE_REPO_RETRIES env var (default 0
  = opt-in, backward compatible)
- Retry applies to helm repo add, helm repo update (incl. ACR), and
  helm registry login with exponential backoff (1s, 2s, 4s, ..., capped 30s)
- Single retryRepoOp helper; per-attempt args/buffer are local to avoid
  state leaking across retries
- Tests cover succeed-after-retry, exhausted-retries, disabled-by-default,
  and regression guards for password-buffer and args-accumulation

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: address PR review (overflow guard, cancellable sleep, flag-override, docs)

Address Copilot review feedback on #2683:

- Cap backoff shift exponent at 5 to prevent time.Duration overflow on
  large --repo-retries values
- Make retry sleep context-aware (sleepCtx) so Ctrl+C aborts the retry
  loop promptly via the ShellRunner context
- Log a concise exit status instead of the verbose ExitError dump, and
  clarify the retry-counter wording ('retry N/M')
- Use -1 sentinel as the CLI default so --repo-retries=0 can explicitly
  disable retries even when HELMFILE_REPO_RETRIES is set
- Align help text and docs: retry applies 'on failure' (not just
  transient errors), document the 0-disables behavior
- Add tests for overflow guard, cancellable sleep, and flag-zero-disables

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: abort retries on canceled context, hide sentinel default, align comment

Address follow-up Copilot review on #2683:

- Fix tight-loop bug: sleepCtx now returns whether it completed vs was
  interrupted by context cancellation, and retryRepoOp aborts the retry
  loop on interruption so Ctrl+C no longer spins into rapid helm calls
- Hide the -1 sentinel from --help by overriding the displayed default
  to 0 (pflag DefValue), matching the documented default while keeping
  the flag-override semantics
- Correct HelmExecOptions.RepoRetry comment: 'on failure' not 'transient
  network errors', matching the actual retry behavior
- Add Test_Retry_AbortsOnCanceledContext covering the no-tight-loop path

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: copy args per retry in RegistryLogin, make cancel test deterministic

Address follow-up Copilot review on #2683:

- RegistryLogin: pass a per-attempt copy of args to execStdIn so its
  internal append (for helm.extra) can't alias the shared slice across
  retries
- Test_Retry_AbortsOnCanceledContext: cancel the context deterministically
  inside the op closure after the first attempt, replacing the flaky
  time.Sleep(20ms) goroutine

Signed-off-by: yxxhero <aiopsclub@163.com>

* fix: return error on unknown managed repo type instead of silent skip

Address Copilot review on #2683: AddRepo logged an error for an unknown
managed type but returned nil, silently succeeding while skipping the
repo add. Now returns an error so misconfigurations fail loudly.

Signed-off-by: yxxhero <aiopsclub@163.com>

---------

Signed-off-by: yxxhero <aiopsclub@163.com>

cmd/root.go

@@ -135,6 +135,13 @@ func setGlobalOptionsForRootCmd(fs *pflag.FlagSet, globalOptions *config.GlobalO
 	fs.BoolVar(&globalOptions.DisableForceUpdate, "disable-force-update", false, `do not force helm repos to update when executing "helm repo add" (Helm 3 only)`)
 	fs.BoolVar(&globalOptions.EnforcePluginVerification, "enforce-plugin-verification", false, `fail plugin installation if verification is not supported (for security purposes)`)
 	fs.BoolVar(&globalOptions.HelmOCIPlainHTTP, "oci-plain-http", false, `use plain HTTP for OCI registries (required for local/insecure registries in Helm 4)`)
+	fs.IntVar(&globalOptions.RepoRetry, "repo-retries", -1, `Number of times to retry "helm repo add/update" and "helm registry login" on failure, with exponential backoff (1s, 2s, 4s, ..., capped at 30s). Set to 0 to disable retries. Overrides "HELMFILE_REPO_RETRIES" OS environment variable when specified`)
+	// The actual default is -1 (a sentinel meaning "flag not set, fall back to
+	// the env var"); display "0" in --help to match the documented default and
+	// avoid confusing users with a negative value.
+	if f := fs.Lookup("repo-retries"); f != nil {
+		f.DefValue = "0"
+	}
 	fs.BoolVarP(&globalOptions.Quiet, "quiet", "q", false, `Silence output. Equivalent to log-level warn. Overrides "HELMFILE_QUIET" OS environment variable when specified`)
 	fs.StringVar(&globalOptions.Kubeconfig, "kubeconfig", "", "Use a particular kubeconfig file")
 	fs.StringVar(&globalOptions.KubeContext, "kube-context", "", `Set kubectl context. Overrides "HELMFILE_KUBE_CONTEXT" OS environment variable when specified. Uses current kubectl context by default`)