feat: aborted-transaction retry policy and client integration

[mlwelles]

Adds a retry layer for aborted Dgraph transactions:

• RetryPolicy / DefaultRetryPolicy and a runner with exponential backoff (retry.go).
• Exposed on the client via a new Client.WithRetry(ctx, policy, fn) method.

Self-contained: retry.go + the WithRetry interface method on Client; builds and tests green. The bulk-loader PR (#19) stacks on this.

Part of a series upstreaming work from a downstream fork; opened for review/discussion.

[cubic-dev-ai]

2 issues found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="retry.go">

<violation number="1" location="retry.go:46">
P2: MaxDelay cap is applied before jitter, so actual backoff can exceed the configured maximum. The `MaxDelay` field is documented as capping the backoff so "No single delay exceeds this," but the `delay()` method applies the cap before adding positive jitter, allowing the final delay to exceed `MaxDelay`.</violation>

<violation number="2" location="retry.go:77">
P2: Negative `MaxRetries` can skip the loop entirely and trigger the panic path.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: MaxDelay cap is applied before jitter, so actual backoff can exceed the configured maximum. The MaxDelay field is documented as capping the backoff so "No single delay exceeds this," but the delay() method applies the cap before adding positive jitter, allowing the final delay to exceed MaxDelay.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At retry.go, line 46:

<comment>MaxDelay cap is applied before jitter, so actual backoff can exceed the configured maximum. The `MaxDelay` field is documented as capping the backoff so "No single delay exceeds this," but the `delay()` method applies the cap before adding positive jitter, allowing the final delay to exceed `MaxDelay`.</comment>

<file context>
@@ -0,0 +1,96 @@
+
+// delay computes the backoff duration for a given attempt (0-indexed).
+// Formula: min(BaseDelay * 2^attempt, MaxDelay) + random(0, delay * Jitter)
+func (p RetryPolicy) delay(attempt int) time.Duration {
+	d := p.BaseDelay * time.Duration(1<<uint(attempt))
+	if d > p.MaxDelay {
</file context>

[cubic-dev-ai]

P2: Negative MaxRetries can skip the loop entirely and trigger the panic path.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At retry.go, line 77:

<comment>Negative `MaxRetries` can skip the loop entirely and trigger the panic path.</comment>

<file context>
@@ -0,0 +1,96 @@
+//	    return client.Insert(ctx, &entity)
+//	})
+func (c client) WithRetry(ctx context.Context, policy RetryPolicy, fn func() error) error {
+	for attempt := range policy.MaxRetries + 1 {
+		err := fn()
+		if err == nil {
</file context>