Bedrock auth broken since v1.0.74 — "Could not load credentials from any providers" despite valid OIDC credentials

Hey there -- our Bedrock-based PR review workflow stopped working yesterday, which lines up with the v1.0.74/v1.0.75 releases. Hoping someone can point us in the right direction.

**What's happening**

Claude Code fails immediately with API Error: Could not load credentials from any providers, despite our OIDC credentials being set up and confirmed working in earlier steps. It never makes an API call (0 tokens in/out).

**Our setup**

- anthropics/claude-code-action@v1
- use_bedrock: true
- OIDC auth via aws-actions/configure-aws-credentials@v5.1.1
- Model: us.anthropic.claude-sonnet-4-5-20250929-v1:0
- Ubuntu 24.04 runner

**_What we've confirmed_**

- The OIDC step succeeds: Authenticated as a private assumed role from AWS IAM STS.
- AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, and AWS_SESSION_TOKEN are all present in the env for subsequent steps
- Claude Code installs fine (v2.1.79), MCP servers connect
- The Bedrock env looks correct:
CLAUDE_CODE_USE_BEDROCK: 1
ANTHROPIC_BEDROCK_BASE_URL: https://bedrock-runtime.us-east-1.amazonaws.com

But then:
```
{
"result": "API Error: Could not load credentials from any providers",
"duration_api_ms": 0,
"num_turns": 1,
"usage": { "input_tokens": 0, "output_tokens": 0 }
}
```

Here's our workflow config:
```
- uses: anthropics/claude-code-action@v1
with:
use_bedrock: true
claude_args: |
--model us.anthropic.claude-sonnet-4-5-20250929-v1:0
--max-turns 40
```

**Timeline**

This was working fine before yesterday. The only thing that changed on our end is the action auto-updating to v1.0.74+. Not sure if the issue is in the action itself or the Claude Code / Agent SDK versions it pulls in (v2.1.79 / v0.2.79).

Happy to provide the full run log if that helps. For now we're pinning to an older SHA as a workaround.

**API Provider**

[ ] Anthropic First-Party API (default)
[X] AWS Bedrock
[ ] GCP Vertex

Start by reproducing the workflow with anthropics/claude-code-action@v1, use_bedrock enabled, and the documented OIDC environment variables. Compare v1.0.74+ with the pinned older SHA and the listed Claude Code and Agent SDK versions; done means Bedrock authentication succeeds and the action makes a nonzero-token API call.

Written by the indexing model from the issue text.