feat: add request.body async getters

[hbenl]

Fixes #38150 and the following tests:

with Chrome/CDP:

• page/network-request-body.spec.ts:
  • "should get request body for file/blob"
  • "should get request body for navigator.sendBeacon api calls"

with BiDi:

• page/network-request-body.spec.ts:
  • "should return correct request body buffer for utf-8 body"
  • "should return request body w/o content-type"
  • "should throw on invalid JSON in post data"
  • "should return body for PUT requests"
  • "should get request body for file/blob"
  • "should get request body for navigator.sendBeacon api calls"

[hbenl]

The failing BiDi tests are all passing locally. CI test results seem flakier than they used to be, perhaps due to the increased number of workers.

[whimboo]

@hbenl mind checking the BiDi job? Two tests are failing - maybe intermittently?

[hbenl]

Those failures are unrelated to this PR, the tests are also failing in other test runs, I've added them to the expectations file.

[github-actions]

Test results for "tests 1"

6 failed
❌ [playwright-test] › playwright.spec.ts:877 › page.pause() should disable test timeout @macos-latest-node20
❌ [playwright-test] › ui-mode-test-network-tab.spec.ts:140 › should format JSON request body @macos-latest-node20
❌ [playwright-test] › ui-mode-test-network-tab.spec.ts:184 › should display list of query parameters (only if present) @macos-latest-node20
❌ [playwright-test] › ui-mode-test-network-tab.spec.ts:353 › should not preserve selection across test runs @macos-latest-node20
❌ [playwright-test] › ui-mode-test-network-tab.spec.ts:252 › should toggle sections inside network details @windows-latest-node20
❌ [playwright-test] › ui-mode-test-network-tab.spec.ts:287 › should copy network request @windows-latest-node20

5 flaky

⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:1082 › cli codegen › should not throw csp directive violation errors `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-page] › page/page-set-input-files.spec.ts:38 › should upload a folder `@firefox-ubuntu-22.04-node20`
⚠️ [firefox-page] › page/page-wait-for-function.spec.ts:104 › should work with strict CSP policy `@firefox-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:183 › should show snapshots for steps `@macos-latest-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:688 › should indicate current test status `@macos-latest-node20`

34681 passed, 691 skipped

---

Merge workflow run.

[github-actions]

Test results for "MCP"

1 failed
❌ [chromium] › mcp/launch.spec.ts:21 › test reopen browser @mcp-macos-15

2829 passed, 121 skipped

---

Merge workflow run.

[whimboo]

Those failures are unrelated to this PR, the tests are also failing in other test runs, I've added them to the expectations file.

Interesting. Do we know since when they started to fail and what caused them given that we were probably green about 4 weeks ago? Or are they new and were not added to the expectation list?

[hbenl]

Interesting. Do we know since when they started to fail and what caused them given that we were probably green about 4 weeks ago? Or are they new and were not added to the expectation list?

One of them is new and has been failing intermittently from the start, the other started failing on 2026-01-09. I'll investigate.

[hbenl]

The 2 failures in the latest run are from new tests that have been failing before (one of them intermittently).