[BUG] AWS Bedrock Custom ARN not working with prompt caching

[wisestmumbler]

Problem (one or two sentences)

AWS Bedrock Custom ARN not working with prompt caching. Previous issues have been opened for this and closed prematurely

There is a PR open for this issue right now:
#10697

Context (who is affected and when)

No one using a custom arn has access to prompt caching - which increases latency, failure rate, and cost

#10697

Reproduction steps

When using aws bedrock as the provider and working with a custom arn there is no option for prompt caching

Expected result

The toggle should be there and true by default

Actual result

The toggle is not there and prompt caching is not working

Variations tried (optional)

Previous bugs have been opened for this but they are closed prematurely

App Version

v3

API Provider (optional)

Amazon Bedrock

Model Used (optional)

Custom ARN

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

[roomote]

I've analyzed this issue and here's my proposed implementation plan:

Root Cause:
The prompt caching toggle is not shown for custom ARN users because supportsPromptCache is set to false in the custom ARN model info at webview-ui/src/components/ui/hooks/useSelectedModel.ts (lines 216-220). The toggle only renders when selectedModelInfo?.supportsPromptCache is truthy in Bedrock.tsx.

Proposed Changes:

1. Modify webview-ui/src/components/ui/hooks/useSelectedModel.ts: Change supportsPromptCache: false to supportsPromptCache: true for the custom ARN case. Since custom ARNs often point to Claude models that support prompt caching, treating this as an advanced option where users know what they are doing makes sense.

2. Modify webview-ui/src/components/settings/providers/Bedrock.tsx: Change the default value of awsUsePromptCache from || false to ?? true so that prompt caching defaults to ON (providing cost savings and latency improvements), while still respecting explicitly set false values via nullish coalescing.

Note: I noticed there is already an open PR #10697 that implements this exact fix. If the maintainers prefer to merge that PR instead, please let me know. Otherwise, I can proceed with this implementation.

Please mention @roomote in a comment saying that you approve this plan, and I'll proceed with the implementation.

[wisestmumbler]

@roomote please continue with the open PR

and note the previous issues that were prematurely closed:
#8669
#10576

[roomote]

I have seen your comment and will continue working on PR #10697. The PR is currently open and all CI checks pass, but it needs to be rebased onto main to stay up-to-date. I will rebase the branch and push the updates.

Note: I have reviewed the previous issues (#8669 and #10576) as well. The fix enables the prompt caching toggle for custom ARN users and defaults the setting to ON.

[roomote]

PR #10697 has been rebased onto main and pushed. All 143 Bedrock tests pass locally, and CI is now running.

Summary of the PR:

• Enables the prompt caching toggle for custom ARN users (treating custom ARN as an advanced option where users know what they are doing)
• Defaults the prompt caching setting to ON for all Bedrock users

The PR is ready for maintainer review: #10697

Feedback welcome!