feat(agents): enable conservative retries by default for transient errors

[MarioCadenas]

What

Agents previously disabled retries entirely — agentStreamDefaults set retry: { enabled: false }. A single transient serving error (5xx, 429, connection reset) would fail the whole turn.

This enables a conservative default that reuses the existing RetryInterceptor (exponential backoff with full jitter, only retries transient/retryable errors):

retry: { enabled: true, attempts: 2, initialDelay: 500, maxDelay: 4_000 }

• Old default: retries off — any transient blip failed the turn.
• New default: at most one extra attempt, 500ms→4s jittered backoff. Non-retryable errors (4xx, AppKitError with isRetryable=false) are still never retried — see isRetryableError in interceptors/retry.ts.

No new retry logic was added; only the default config value changed.

Streaming / non-idempotency safety (the scope applied)

The agents plugin consumes retry in exactly one place: the streaming /chat path via executeStream (agents.ts:1162). This change is streaming-replay-safe by construction, not by configuration:

• In executeStream, the interceptor chain wraps wrappedFn = async () => fn(signal), where fn is the async generator function for the turn.
• Calling a generator function returns the generator object synchronously without running its body. So wrappedFn resolves immediately and the RetryInterceptor sees success on attempt 1.
• Token emission and tool dispatch happen later, during yield* iteration — which runs outside the interceptor chain.
• Therefore a transient error thrown after the first streamed event surfaces during iteration and is never seen by the retry loop. There is no path by which retry can re-emit tokens or re-run a tool side-effect (no double-charge / duplicate writes).
• The only thing retried is a transient failure during generator setup, before any output — which is safe and idempotent.

The non-streaming /invocations and /responses path (_runAgentNonStreaming) does not route through execute()/executeStream() at all, so this default does not affect it.

Tests

Added packages/appkit/src/plugins/agents/tests/defaults.test.ts:

• asserts the conservative default values (enabled, attempts === 2, bounded backoff caps).
• proves no mid-stream replay: drives the real RetryInterceptor exactly as executeStream does, throws a 5xx after the first yielded token, and asserts the generator body ran once and the tool side-effect fired once (no replay).
• proves a transient error during generator setup (before output) is retried.

Verification

• pnpm --filter=@databricks/appkit typecheck — clean.
• agents suite: 120 passed; retry.test.ts: 19 passed; new defaults.test.ts: 3 passed.
• biome check on changed files — no fixes/errors.

[github-actions]

📦 Bundle size report

Compared against bundle-size-baseline.json (main).

@databricks/appkit

npm tarball (packed): 722 KB (+20 KB) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	746 KB (+18 KB)	261 KB (+6.7 KB)
Type declarations	281 KB (+6.4 KB)	96 KB (+2.4 KB)
Source maps	1.5 MB (+35 KB)	487 KB (+13 KB)
Other	11 KB	3.7 KB
Total	2.5 MB (+60 KB)	848 KB (+22 KB)

Per-entry composition (own code — deps external (as shipped))

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
.	80 KB (+1.1 KB)	2.5 KB	82 KB (+1.1 KB)	external	262 KB (+3.4 KB)
./beta	39 KB (+476 B)	231 B (+1 B)	40 KB (+477 B)	external	118 KB (+1.3 KB)
./type-generator	19 KB	0 B	19 KB	external	54 KB

Chunks:

Entry	Chunk	Load	Size (gz)
.	index.js	initial	76 KB
.	utils.js	initial	4.0 KB
.	remote-tunnel-manager.js	lazy	2.5 KB
./beta	beta.js	initial	30 KB
./beta	databricks.js	initial	5.8 KB
./beta	service-context.js	initial	3.2 KB
./beta	client-options.js	initial	220 B
./beta	databricks.js	lazy	128 B
./beta	index.js	lazy	103 B
./type-generator	index.js	initial	19 KB

@databricks/appkit-ui

npm tarball (packed): 295 KB (+4 B) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	350 KB	116 KB
Type declarations	201 KB	72 KB (+2 B)
Source maps	669 KB	218 KB (-2 B)
CSS	16 KB	3.3 KB
Total	1.2 MB	410 KB

Per-entry composition (consumer bundle — deps bundled, peerDeps external)

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
./js	4.3 KB	49 KB	54 KB	208 KB	12 KB
./js/beta	20 B	0 B	20 B	0 B	0 B
./react	428 KB	49 KB	476 KB	1.3 MB	163 KB
./react/beta	20 B	0 B	20 B	0 B	0 B

Chunks:

Entry	Chunk	Load	Size (gz)
./js	index.js	initial	4.2 KB
./js	chunk	initial	120 B
./js	apache-arrow	lazy	49 KB
./js/beta	beta.js	initial	20 B
./react	index.js	initial	426 KB
./react	tslib	initial	2.1 KB
./react	apache-arrow	lazy	49 KB
./react/beta	beta.js	initial	20 B