feat(stream): make SSE maxEventSize configurable end-to-end

[calvarjorge]

Summary

Makes the SSE maxEventSize limit actually overridable by application code. Two commits:

1. fix(stream) (existing) — raise the default event limit to 5 MiB, honour a per-call maxEventSize (it was read off the StreamManager instance, so per-call values passed via executeStream({ stream }) type-checked and were then silently ignored), and measure UTF-8 bytes instead of String.length.

2. feat(stream) (new) — expose streamConfig on BasePluginConfig.

Why the second commit

Even after the per-call fix, no shipped path could reach the knob:

• Plugin always constructed new StreamManager() with no options, so the constructor-level defaults (including maxEventSize) were unreachable through plugin config.
• The built-in analytics plugin — the one that emits Event exceeds max size — builds its StreamExecutionSettings with no stream field, so the per-call override never reached it.

Result: an app hitting the limit had no way to raise it without patching AppKit.

Change

Add streamConfig?: StreamConfig to BasePluginConfig and forward it to the plugin's StreamManager. A per-call executeStream({ stream }) override still layers on top of these instance defaults.

createApp({
  plugins: [
    analytics({
      streamConfig: { maxEventSize: 20 * 1024 * 1024 }, // 20 MiB, overrides the 5 MiB default
    }),
  ],
});

Notes

• Per-plugin: each plugin instance can carry its own stream limits.
• Client side must be raised in tandem — a browser using connectSSE's default maxBufferSize (5 MiB) will reject a larger event; pass connectSSE({ maxBufferSize }) to match.

Testing

• New plugin tests assert streamConfig is forwarded to the StreamManager constructor (and undefined when unset).
• plugin.test.ts (54) and stream/tests/ (112) pass.

This pull request and its description were written by Isaac.

[github-actions]

📦 Bundle size report

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

@databricks/appkit

npm tarball (packed): 1.0 MB (+1.5 KB) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	1.0 MB (+1.2 KB)	376 KB (+457 B)
Type declarations	385 KB (+533 B)	136 KB (+186 B)
Source maps	2.1 MB (+2.4 KB)	705 KB (+858 B)
Other	11 KB	3.7 KB
Total	3.5 MB (+4.1 KB)	1.2 MB (+1.5 KB)

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

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
.	95 KB (+6 B)	2.5 KB	97 KB (+6 B)	external	311 KB (+16 B)
./beta	75 KB (+189 B)	457 B	75 KB (+189 B)	external	226 KB (+498 B)
./testing	17 KB	0 B	17 KB	external	50 KB
./tsdown	520 B	0 B	520 B	external	813 B
./type-generator	22 KB	0 B	22 KB	external	65 KB

Chunks:

Entry	Chunk	Load	Size (gz)
.	index.js	initial	91 KB
.	utils.js	initial	4.0 KB
.	remote-tunnel-manager.js	lazy	2.5 KB
./beta	beta.js	initial	59 KB
./beta	stream-manager.js	initial	5.8 KB
./beta	wide-event-emitter.js	initial	3.2 KB
./beta	databricks.js	initial	3.2 KB
./beta	configuration.js	initial	2.1 KB
./beta	service-context.js	initial	1.3 KB
./beta	client.js	initial	434 B
./beta	client-options.js	initial	220 B
./beta	supervisor-api.js	lazy	193 B
./beta	databricks.js	lazy	142 B
./beta	index.js	lazy	122 B
./testing	index.js	initial	17 KB
./tsdown	index.js	initial	520 B
./type-generator	index.js	initial	22 KB

@databricks/appkit-ui

npm tarball (packed): 350 KB (+13 B) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	395 KB	132 KB
Type declarations	229 KB (+23 B)	84 KB (+6 B)
Source maps	766 KB (+1 B)	253 KB
CSS	16 KB	3.2 KB
Total	1.4 MB (+24 B)	473 KB (+6 B)

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

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
./js	5.3 KB	49 KB	55 KB	208 KB	14 KB
./js/beta	20 B	0 B	20 B	0 B	0 B
./react	432 KB	49 KB	481 KB	1.3 MB	177 KB
./react/beta	1.0 KB	0 B	1.0 KB	0 B	1.9 KB

Chunks:

Entry	Chunk	Load	Size (gz)
./js	index.js	initial	5.2 KB
./js	chunk	initial	120 B
./js	apache-arrow	lazy	49 KB
./js/beta	beta.js	initial	20 B
./react	index.js	initial	430 KB
./react	tslib	initial	2.1 KB
./react	apache-arrow	lazy	49 KB
./react/beta	beta.js	initial	1.0 KB

[github-actions]

🤖 AppKit PR bot

🔬 Run evals

Start an eval for this PR from the evals-monitor app: Go to Evals Monitor →

📦 Try this PR's app template

Scaffolds a new app from this PR's SDK build. Run it in any folder (requires the GitHub CLI — gh auth login — and the Databricks CLI):

gh run download 33636926482 -R databricks/appkit -n appkit-template-0.69.2-pr.2972984-fix-stream-config-per-call-overrides-568 -D appkit-pr-568 \
  && unzip -o "appkit-pr-568/appkit-template-0.69.2-pr.2972984-fix-stream-config-per-call-overrides-568.zip" -d "appkit-pr-568" \
  && databricks apps init --template "appkit-pr-568"

The template pins @databricks/appkit and @databricks/appkit-ui to tarballs built from this branch, so the scaffolded app runs against this PR's code.