perf(eve): bound sandbox batch writes on providers without native batching by cmpadden · Pull Request #5328 · vercel/eve

cmpadden · 2026-10-23T22:22:27Z

Summary

SandboxSession.writeFiles already exists and the Vercel adapter already resolves every write path and then sends one native sandbox.writeFiles batch, so the remaining gap from #4774 was the fallback path and the contract. Providers without a native batch API, just-bash and Docker, wrote strictly one file at a time and ignored an abort until their next provider call. They now write with a bounded number of writes in flight, 16 locally and 8 for Docker exec, and reject an already-aborted batch before writing anything. The sandbox docs now state the partial-failure contract: a batch is not atomic, and eve rolls nothing back. Related to #4774.

The benchmark the issue asks for is not included. It needs a Vercel sandbox with a fixed region and configuration, which this change set cannot run, so this PR makes no speedup claim. Please keep #4774 open for the measurement.

Validation

pnpm --filter eve exec vitest run --config vitest.unit.config.ts src/execution/sandbox (19 files, 194 tests)
pnpm lint, pnpm typecheck, pnpm docs:check, pnpm guard:invariants

Checklist

I added tests and documentation where relevant
I added a changeset if this touches the published eve package
DCO sign-off passes for every commit (git commit --signoff)

…ching Signed-off-by: Colton Padden <cmpadden@users.noreply.github.com>

vercel · 2026-10-23T22:22:36Z

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
eve-docs	Ready	Preview, v0	Oct 23, 2026 10:25pm UTC
eve-pkg	Ready	Preview, v0	Oct 23, 2026 10:25pm UTC

roboeve · 2026-10-23T22:26:00Z

+    async writeFiles({ abortSignal, files }) {
+      abortSignal?.throwIfAborted();
+      // A batch is not atomic: files written before a rejection stay written.
+      await mapConcurrent(


Running writes concurrently changes what happens when a batch lists the same path twice. Before this change the writes ran one after another, so the last entry won. Vercel's tar batch also ends with the last entry. Here, both entries' writeFiles run against the same file at once, and Node says that's unsafe (fsPromises.writeFile: "unsafe to use fsPromises.writeFile() multiple times on the same file without waiting for the promise to be settled"). Docker has the same problem: two cat > execs racing on one path (line 157 of docker-connection.ts).

Repro with just-bash's ReadWriteFs, running this PR's per-file op (mkdir and then writeFile) for [1 MB, "small"] on one path at the same time: the last-listed "small" was lost in 50 of 50 runs. The file kept the earlier 1 MB content. Duplicates can happen through the public sandbox.writeFiles(), and also in populate() when skills fall back to skills/ under the workspace root and a workspace file uses the same relative path.

The simplest fix is to keep only the last entry per resolved path in createConnectionSession().writeFiles (session.ts), for example [...new Map(files.map((f) => [f.path, f])).values()]. That keeps last-wins on every provider, including custom ones, and neither binding has to handle it.

roboeve · 2026-10-23T22:26:00Z


+### Write several files at once
+
+`writeFiles()` writes a batch of files from raw bytes, which is much faster than one call per file:


"much faster than one call per file" is a speed claim nobody has measured, and the PR description explicitly makes no speedup claim. Say what the batch does instead, e.g. "writeFiles() writes several files from raw bytes in one call:". The paragraph below already explains how each provider sends the batch.

github-actions · 2026-10-23T22:27:27Z

Bundle + Package Summary: `apps/fixtures/weather-agent`

Key takeaways

No notable deltas vs main (13399a5).

Delta vs `main (13399a5)`

Area	Metric	Baseline	Current	Delta
Package	Packed tarball	7.77 MB	7.77 MB	-586 B ✅
Package	Unpacked publish size	27.30 MB	27.30 MB	+1.2 kB ⚠️
Package	Installed footprint	75.61 MB	75.61 MB	+1.2 kB ⚠️
Package	Published files	4222	4222	0
Package	Installed files	8215	8215	0
Package	Installed package instances	34	34	0
Package	Distinct installed package names	32	32	0
Package	Installed dependency edges	51	51	0
Package	Installed optional peer edges	8	8	0
Runtime	Unique function payloads	2	2	0
Runtime	Total function bytes	20.90 MB	20.90 MB	-80 B ✅
Runtime	Public routes	18	18	0

Changed function payloads vs main (13399a5) (2)

Function	Status	Baseline	Current	Delta	Route changes
`functions/__server.func`	changed	10.45 MB	10.45 MB	-40 B ✅	none
`functions/.well-known/workflow/v1/flow.func`	changed	10.45 MB	10.45 MB	-40 B ✅	none

`eve init` install

Metric	Baseline	Current	Delta
Installed footprint	113.99 MB	113.99 MB	+1.2 kB ⚠️
Installed packages	97	97	0
dependencies	4	4	0
devDependencies	2	2	0
Dependency package bytes	45.70 MB	45.70 MB	+1.2 kB ⚠️
devDependency package bytes	5.11 MB	5.11 MB	0 B ➖

Build Metadata

Preset: vercel
Nitro: nitro@3.0.260903-beta
Output directory: apps/fixtures/weather-agent/.vercel/output
Build metadata timestamp: 2026-10-23T22:26:38.231Z
Route aliases: 18 public, 1 internal (19 total aliases)
Vercel routes in config: 21
Severity legend: 🔴 dominant/large, 🟠 notable, 🟡 watch, ⚪ small

Package Drill-Down

Package Details

Package: eve@0.83.0
Package directory: packages/eve
Tarball: 7.77 MB (eve-0.83.0.tgz)
Unpacked payload: 27.30 MB across 4222 published files
Installed footprint: 75.61 MB across 8215 installed files
Installed root package: 27.30 MB
Installed dependencies: 48.31 MB
Installed package instances: 34
Distinct installed package names: 32
Installed dependency edges: 51
Installed optional peer edges: 8
Runtime dependencies: 2
Peer dependencies: 6 (5 optional)

Installed footprint is measured from an isolated temporary npm install of the packed tarball.
Graph metrics read only package.json files in package directories directly beneath a node_modules boundary, including nested boundaries. Each directory is one package instance; distinct names come from those manifests. Dependency edges count each unique name in dependencies or optionalDependencies per instance; optional peer edges count peerDependencies marked optional.

Heavy installed dependencies

eve: 27.30 MB (36.1%)
@rolldown/binding-linux-x64-gnu: 19.89 MB (26.3%)
ai: 8.37 MB (11.1%)
zod: 6.15 MB (8.1%)
undici: 3.58 MB (4.7%)

Publish payload breakdown

Published file size
🟠 dist/src/compiled/shadcn-registry/index.js       [#####...................] 3.85 MB 14.1%
🟠 dist/src/compiled/@photon-ai/chat-adapter-ime... [###.....................] 2.29 MB 8.4%
🟠 dist/src/compiled/run/index.js                   [#.......................] 1.00 MB 3.7%
🟡 dist/src/compiled/@vercel/blob/index.js          [#.......................] 604.9 kB 2.2%
🟡 dist/src/compiled/_chunks/workflow/undici-D-I... [#.......................] 521.9 kB 1.9%
🔴 Other published files                            [########################] 19.03 MB 69.7%

Installed footprint breakdown

Installed package size
🔴 eve                             [########################] 27.30 MB 36.1%
🔴 @rolldown/binding-linux-x64-gnu [#################.......] 19.89 MB 26.3%
🔴 ai                              [#######.................] 8.37 MB 11.1%
🔴 zod                             [#####...................] 6.15 MB 8.1%
🟠 undici                          [###.....................] 3.58 MB 4.7%
🟠 nitro                           [##......................] 1.89 MB 2.5%
🔴 Other installed packages        [#######.................] 8.43 MB 11.2%

Runtime dependencies (2)

Package	Range	Notes
`nitro`	`3.0.260903-beta`
`undici`	`8.10.2`

Peer dependencies (6)

Package	Range	Notes
`@opentelemetry/api`	`^1.0.0`	optional peer
`ai`	`catalog:`
`braintrust`	`^3.0.0`	optional peer
`chat`	`^4.42.0`	optional peer
`dd-trace`	`^6.13.0`	optional peer
`just-bash`	`^3.1.0`	optional peer

eve init install drill-down

`eve init` install details

Command: eve init my-agent
Package manager: npm
Installed footprint: 113.99 MB across 10132 installed files
Installed packages: 97 total (91 transitive-only)
dependencies: 4 direct packages totaling 45.70 MB
devDependencies: 2 direct packages totaling 5.11 MB
Other transitive package files: 63.18 MB

Installed footprint is measured from an isolated temporary eve init my-agent using the current packed eve tarball.

Heavy installed dependencies

@typescript/typescript-linux-x64: 27.95 MB (24.5%)
eve: 27.30 MB (23.9%)
@rolldown/binding-linux-x64-gnu: 19.89 MB (17.5%)
zod: 9.76 MB (8.6%)
ai: 8.37 MB (7.3%)

Installed footprint breakdown

Installed package size
🔴 @typescript/typescript-linux-x64 [########################] 27.95 MB 24.5%
🔴 eve                              [#######################.] 27.30 MB 23.9%
🔴 @rolldown/binding-linux-x64-gnu  [#################.......] 19.89 MB 17.5%
🔴 zod                              [########................] 9.76 MB 8.6%
🔴 ai                               [#######.................] 8.37 MB 7.3%
🟠 undici                           [###.....................] 3.58 MB 3.1%
🔴 Other installed packages         [###############.........] 17.16 MB 15.0%

dependencies (4)

Package	Range	Installed size	Share
`@vercel/connect`	`2.5.2`	276.3 kB	0.2%
`ai`	`^7.0.137`	8.37 MB	7.3%
`eve`	`file:eve-0.83.0.tgz`	27.30 MB	23.9%
`zod`	`4.5.4`	9.76 MB	8.6%

devDependencies (2)

Package	Range	Installed size	Share
`@types/node`	`24.x`	2.61 MB	2.3%
`typescript`	`7.0.2`	2.50 MB	2.2%

Function Drill-Down

Payload Size Graph

Unique function payload size and share of total
🔴 functions/.well-known/workflow/v1/flow.func     [########################] 10.45 MB 50.0%
🔴 functions/__server.func                         [########################] 10.45 MB 50.0%

Top Function Payloads

🟠 functions/.well-known/workflow/v1/flow.func • 1 public route • 10.45 MB

Metric	Value
Public routes	`/.well-known/workflow/v1/flow`
Runtime	`nodejs24.x`
Handler	`index.mjs`
Payload	10.45 MB
Function files	10.45 MB across 121 files
Traced dependencies	0 B
Signal	🟠 Bundled file `_chunks/vercel.web.mjs` is 2.48 MB (23.8%)

🟠 🔎 Dependency Analysis

📦 Bundled files:

Bundled file size
🟠 _chunks/vercel.web.mjs                         [#############...........] 2.48 MB 23.8%
🟡 _libs/undici.mjs                               [#####...................] 994.5 kB 9.5%
🟡 _chunks/sandbox2.mjs                           [####....................] 815.0 kB 7.8%
🟡 _chunks/compiled-artifacts-instrumentation.mjs [####....................] 732.3 kB 7.0%
🟡 _chunks/token-util-Bla5Z0G9.mjs                [####....................] 704.5 kB 6.7%
🔴 Other bundled files                            [########################] 4.72 MB 45.2%

🧾 Vercel Config

{
  "handler": "index.mjs",
  "launcherType": "Nodejs",
  "shouldAddHelpers": false,
  "supportsResponseStreaming": true,
  "runtime": "nodejs24.x",
  "maxDuration": "max",
  "experimentalTriggers": [
    {
      "type": "queue/v2beta",
      "topic": "__eve776561746865722d6167656e74_wkf_workflow_*",
      "consumer": "default",
      "retryAfterSeconds": 5,
      "initialDelaySeconds": 0
    }
  ],
  "environment": {
    "WORKFLOW_PRECONDITION_GUARD": "1"
  }
}

🟠 functions/__server.func • 17 public routes, 1 internal alias • 10.45 MB

Metric	Value
Public routes	`/` `/.well-known/workflow/v1/webhook/[token]` `/eve/v1/callback/[token]` `/eve/v1/connections/[name]/callback/[attemptId]/[token]` `/eve/v1/connections/[name]/callback/[token]` `/eve/v1/health` `/eve/v1/info` `/eve/v1/session` `/eve/v1/session/[parentSessionId]/subagents/[callId]/[childSessionId]/stream` `/eve/v1/session/[sessionId]` `/eve/v1/session/[sessionId]/cancel` `/eve/v1/session/[sessionId]/clear` `/eve/v1/session/[sessionId]/compact` `/eve/v1/session/[sessionId]/reset` `/eve/v1/session/[sessionId]/stream` `/eve/v1/session/[sessionId]/stubs` `/eve/v1/task-input/[token]`
Internal aliases	`/__server`
Runtime	`nodejs24.x`
Handler	`index.mjs`
Payload	10.45 MB
Function files	10.45 MB across 121 files
Traced dependencies	0 B
Signal	🟠 Bundled file `_chunks/vercel.web.mjs` is 2.48 MB (23.8%)

🟠 🔎 Dependency Analysis

📦 Bundled files:

Bundled file size
🟠 _chunks/vercel.web.mjs                         [#############...........] 2.48 MB 23.8%
🟡 _libs/undici.mjs                               [#####...................] 994.5 kB 9.5%
🟡 _chunks/sandbox2.mjs                           [####....................] 815.0 kB 7.8%
🟡 _chunks/compiled-artifacts-instrumentation.mjs [####....................] 732.3 kB 7.0%
🟡 _chunks/token-util-Bla5Z0G9.mjs                [####....................] 704.5 kB 6.7%
🔴 Other bundled files                            [########################] 4.72 MB 45.2%

🧾 Vercel Config

{
  "handler": "index.mjs",
  "launcherType": "Nodejs",
  "shouldAddHelpers": false,
  "supportsResponseStreaming": true,
  "runtime": "nodejs24.x"
}

Build Timing: `e2e/fixtures/agent-tools-sandbox`

This is an informational timing measurement inside eve build, from preflight through publication. Output-size measurement and profile writing are excluded.

Build mode: deployable Vercel build with sandbox template prewarm included.

Build pipeline: 3.96 s -> 3.75 s (-213.6 ms) vs main (13399a5).
Timing is informational: shared GitHub runners are too variable for a hard timing budget.

Detailed phase timings vs `main (13399a5)`

Phase	Baseline	Current	Delta
`extension.check`	0.5 ms	0.5 ms	0.0 ms
`project.resolve`	0.4 ms	0.4 ms	0.0 ms
`workspace.create`	0.6 ms	0.6 ms	0.0 ms
`host.prepare`	758.4 ms	539.2 ms	-219.2 ms
`vercel.service-prefix.resolve`	2.0 ms	1.9 ms	-0.1 ms
`nitro.create`	734.9 ms	692.2 ms	-42.7 ms
`sandbox.prewarm`	388.5 ms	376.0 ms	-12.5 ms
`nitro.cache.prepare`	0.2 ms	0.2 ms	0.0 ms
`nitro.prepare`	0.8 ms	0.8 ms	0.0 ms
`nitro.public-assets`	0.8 ms	0.8 ms	0.0 ms
`nitro.prerender`	0.6 ms	0.6 ms	0.0 ms
`nitro.bundle`	1.92 s	1.97 s	+46.6 ms
`nitro.cache.write`	0.4 ms	0.4 ms	0.0 ms
`vercel.workflow-function.materialize`	56.2 ms	56.2 ms	0.0 ms
`agent-summary.emit`	0.6 ms	0.6 ms	0.0 ms
`connect-manifest.emit`	0.3 ms	0.4 ms	+0.1 ms
`nitro.close`	0.1 ms	0.1 ms	0.0 ms
`output.publish`	3.5 ms	3.6 ms	+0.1 ms
`workspace.remove`	2.9 ms	3.1 ms	+0.2 ms

perf(eve): bound sandbox batch writes on providers without native bat…

ab9b5b6

…ching Signed-off-by: Colton Padden <cmpadden@users.noreply.github.com>

vercel Bot deployed to Preview – eve-pkg October 23, 2026 22:23

View deployment

vercel Bot deployed to Preview – eve-docs October 23, 2026 22:25

View deployment

roboeve Bot reviewed Oct 23, 2026

View reviewed changes

Navigation Menu

Repository navigation

perf(eve): bound sandbox batch writes on providers without native batching - #5328

perf(eve): bound sandbox batch writes on providers without native batching#5328
cmpadden wants to merge 1 commit into
mainfrom
agent/sandbox-batched-writes

cmpadden commented Oct 23, 2026

Uh oh!

vercel Bot commented Oct 23, 2026 •

edited

Loading

Uh oh!

roboeve Bot Oct 23, 2026

Uh oh!

roboeve Bot Oct 23, 2026

Uh oh!

github-actions Bot commented Oct 23, 2026

Package Details

`eve init` install details

Payload Size Graph

Top Function Payloads

Uh oh!

This branch was successfully deployed

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant


		### Write several files at once

		`writeFiles()` writes a batch of files from raw bytes, which is much faster than one call per file:

Conversation

cmpadden commented Oct 23, 2026

Summary

Validation

Checklist

Uh oh!

vercel Bot commented Oct 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

roboeve Bot Oct 23, 2026

Choose a reason for hiding this comment

Uh oh!

roboeve Bot Oct 23, 2026

Choose a reason for hiding this comment

Uh oh!

github-actions Bot commented Oct 23, 2026

Bundle + Package Summary: apps/fixtures/weather-agent

Delta vs main (13399a5)

eve init install

Package Details

eve init install details

Payload Size Graph

Top Function Payloads

Build Timing: e2e/fixtures/agent-tools-sandbox

Uh oh!

This branch was successfully deployed

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

vercel Bot commented Oct 23, 2026 •

edited

Loading

Bundle + Package Summary: `apps/fixtures/weather-agent`

Delta vs `main (13399a5)`

`eve init` install

`eve init` install details

Build Timing: `e2e/fixtures/agent-tools-sandbox`