fix(ai-isolate-cloudflare): accumulate toolResults across rounds

[Sriketk]

Summary

The Cloudflare isolate driver wipes toolResults between need_tools rounds (packages/typescript/ai-isolate-cloudflare/src/isolate-driver.ts:178). wrap-code uses sequential tc_<idx> ids that are re-derived from scratch every time the Worker re-executes user code, so prior-round results must stay in the cache. With the wipe, multi-tool programs like:

const x = await A();
const y = await B();
return x + y;

ping-pong between {tc_0} and {tc_1}:

round	sent toolResults	worker reaction
1	(none)	throws on tc_0
2	{tc_0}	tc_0 cached → throws on tc_1
3	{tc_1} (pre-fix)	tc_0 missing → throws on tc_0 again
4	{tc_0}	tc_1 missing → throws on tc_1 again
...	...	until MaxRoundsExceeded

Single-tool code worked because only one cache entry was ever needed in a given round.

Fix

One-line change: toolResults = {} → toolResults = { ...(toolResults ?? {}) }. Within an execute() call's round loop only — toolResults is local to execute(), so each new execute() still starts fresh (independent code, independent ids).

Why this slipped through

Existing isolate-driver.test.ts cases:

• All need_tools cases are single-round (need_tools → done).
• IDs in tests use ad-hoc shapes like add_1, getA_1 — never wrap-code's real tc_<idx> format. The end-to-end contract between driver and wrap-code was never validated.
• The MaxRoundsExceeded test loops the same tool, so doesn't exercise the multi-tool ping-pong.

Test plan

Adds accumulates toolResults across rounds for sequential tool calls to tests/isolate-driver.test.ts. Uses tc_<idx>-shaped ids matching wrap-code and asserts round 3 carries both tc_0 and tc_1.

• New test fails on prior implementation (expected {success:true, value:'a'}, received undefined for tc_0 in round 3)
• All 16 driver tests pass with the fix (pnpm vitest run tests/isolate-driver.test.ts)
• Live repro against deployed Worker (cobalt-sandbox.sriketk5.workers.dev) confirms multi-tool code converges in 3 rounds post-fix

Related

Discovered while running multi-tool code through @tanstack/ai-isolate-cloudflare@0.1.8 from a Cobalt MCP integration. Independent of #523 (which ports the worker from unsafe_eval to worker_loader); this fix touches isolate-driver.ts only and applies to both the legacy and ported binding paths.

Summary by CodeRabbit

• Bug Fixes

  • Fixed Cloudflare isolate driver behavior to preserve tool results across successive execution rounds, preventing premature round exhaustion and errors in multi-tool workflows.

• Tests

  • Added a regression test that simulates sequential tool calls to verify tool results are accumulated and retained across multiple rounds.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 2c56402d-b2b8-4068-8e51-84a2ad4fe01c

📥 Commits

Reviewing files that changed from the base of the PR and between ed7240f and 5fd3edc.

📒 Files selected for processing (1)

• .changeset/accumulate-tool-results.md

🚧 Files skipped from review as they are similar to previous changes (1)

• .changeset/accumulate-tool-results.md

---

📝 Walkthrough

Walkthrough

The Cloudflare isolate driver is fixed to accumulate toolResults across multiple tool-execution rounds instead of resetting to empty each round, preventing tool-ID reuse from causing round exhaustion. A regression test validates multi-tool sequential behavior.

Changes

Tool Results Accumulation Fix

Layer / File(s)	Summary
Core Logic Fix packages/typescript/ai-isolate-cloudflare/src/isolate-driver.ts	In CloudflareIsolateContext.execute, toolResults is now carried forward across rounds by cloning prior results instead of resetting to {} each iteration. Inline comments explain why sequential tc_<idx> tool IDs require result retention.
Regression Test packages/typescript/ai-isolate-cloudflare/tests/isolate-driver.test.ts	New test case accumulates toolResults across rounds for sequential tool calls verifies that toolResults from tc_0 and tc_1 are both present in the final request POST body after three worker rounds.
Changelog .changeset/accumulate-tool-results.md	Patch release entry documents the toolResults accumulation fix and notes the new end-to-end regression test covering previously missing multi-tool behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A rabbit hops through tool rounds with glee,
No more results lost, hooray!
Sequential tools now dance, tc_0 and tc_1 stay,
Cloudflare's isolate, both safe and spry! 🌟

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely summarizes the main change: fixing the Cloudflare isolate driver to accumulate toolResults across rounds instead of wiping them.
Description check	✅ Passed	The description is comprehensive and follows the template structure with clear sections covering changes, test plan, and checklist items marked appropriately.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[nx-cloud]

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---

☁️ Nx Cloud last updated this comment at 2026-05-07 09:00:21 UTC

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commit: 5fd3edc