feat: StreamThreadException investigation spike for Bing Ads source

[devin-ai-integration]

StreamThreadException investigation and fix (spike, do not merge)

Summary

This spike PR investigates and proposes a fix for issue #8301 - a StreamThreadException in the Bing Ads source connector where the campaign_labels stream fails with:

'utf-8' codec can't decode byte 0x8b in position 1: invalid start byte

Root Cause: Byte 0x8b is the GZIP magic number, indicating that GZIP-compressed data is being incorrectly passed to a UTF-8 decoder. This occurs when the CompositeRawDecoder's parser selection logic fails to detect GZIP content (likely due to missing Content-Encoding headers), causing compressed data to be treated as plain text.

Proposed Solution: Enhanced CompositeRawDecoder with auto-detection of GZIP content by magic bytes, better error handling, and graceful fallback mechanisms.

Review & Testing Checklist for Human

🔴 High Risk - 5 Critical Items

• Validate Root Cause Analysis: Review the investigation document and confirm that GZIP magic byte detection is the correct approach for this issue
• Test Reproduction Script: Run test_gzip_utf8_issue.py in a proper environment to verify it reproduces the exact error (had import issues locally)
• Evaluate Integration Strategy: Decide whether to extend existing CompositeRawDecoder or create new implementation - current proposal creates separate class
• End-to-End Testing: Test the proposed fix with actual Bing Ads connector campaign_labels stream to verify it resolves the issue
• Impact Assessment: Review if auto-detection of GZIP content could affect other connectors that use CompositeRawDecoder

Recommended Test Plan:

1. Set up Bing Ads connector with valid credentials
2. Sync campaign_labels stream to reproduce the error
3. Apply the proposed fix and verify error is resolved
4. Test other Bing Ads streams to ensure no regressions
5. Run connector test suite to validate broader impact

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    Issue["Issue #8301<br/>StreamThreadException<br/>campaign_labels"]
    
    BingAds["airbyte/airbyte-integrations/<br/>connectors/source-bing-ads/<br/>manifest.yaml"]:::context
    CompositeDecoder["airbyte_cdk/sources/declarative/<br/>decoders/composite_raw_decoder.py"]:::context
    ConcurrentSource["airbyte_cdk/sources/concurrent_source/<br/>concurrent_read_processor.py"]:::context
    
    Investigation["SPIKE_INVESTIGATION.md"]:::major-edit
    TestScript["test_gzip_utf8_issue.py"]:::major-edit
    ProposedFix["fix_gzip_parser_selection.py"]:::major-edit
    
    Issue --> Investigation
    Issue --> TestScript
    Issue --> ProposedFix
    
    BingAds --> CompositeDecoder
    CompositeDecoder --> ConcurrentSource
    ConcurrentSource --> Issue
    
    Investigation --> CompositeDecoder
    TestScript --> CompositeDecoder
    ProposedFix --> CompositeDecoder
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• Session Details: Requested by @aaronsteers | Devin Session
• Spike Nature: This is investigation work with a proposed solution - not production-ready code
• Import Issues: Test script had dependency issues when run locally, may need environment setup
• Architecture Decision: Proposed fix creates new class rather than modifying existing CompositeRawDecoder - integration approach needs decision
• Limited Testing: No actual Bing Ads connector testing performed - purely theoretical based on code analysis
• Concurrent Framework: Issue occurs specifically in concurrent source processing, not traditional declarative streams

[devin-ai-integration]

Original prompt from API User

Comment from @aaronsteers: /ai-fix

Create a spike PR (or a pair of PRs if needed). Make sure you read all the comments on this issue before you start. Do not wait for confirmation. Make sure your PR titles include '(spike, do not merge)' and make sure you post those links here in a comment for reference.

Especially important is Christo's clarification here:

> One issue is that this ticket is actually a bit misleading, the Sentry alert is bucketing multiple errors together that are unrelated. The CSV parsing issue was first encountered 19 hours ago and the error message we're actually looking into is:
> 
> 

IMPORTANT: The user will expect a response posted back to the PR. You should post exactly one comment back to the respective issue PR. If the user requested a code change or PR, your comment should contain a link to the PR. Assume the user has no access to your session or conversation thread unless/until you respond back to them.

Issue #8301 by @octavia-squidington-iii: Source: Bing Ads - Error: airbyte_cdk.sources.concurrent_source.stream_thread_exception.StreamThreadException: , (via Sentry)

Issue URL: https://github.com/airbytehq/oncall/issues/8301

Please use playbook macro: !issue_fix

PLAYBOOK_md:
# AI Fix Playbook

You are AI Fix Devin, an expert at reproducing and fixing Airbyte-related issues.

## Context
You are working on the issue linked above in context. You will also need to pull issue comments for full context.

## Rule: Immediate Issue Comment After PR Creation
**MANDATORY REQUIREMENT**: If you create a PR during an AI Fix workflow, your **first action** after creating the PR must be to create a comment on the originating issue. If you cannot create a PR, likewise, your action should be to comment back to the issue.

## Your Task: Reproduce and Fix

1. **Analysis**: Read the complete issue content including all comments for full context.

2. **Research**: Check the internet and Airbyte repositories for:
   - Similar issues and their solutions... (2101 chars truncated...)

[devin-ai-integration]

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[github-actions]

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Testing This CDK Version

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# Run the CLI from this branch:
uvx 'git+https://github.com/airbytehq/airbyte-python-cdk.git@devin/1755287258-bing-ads-stream-thread-exception-spike#egg=airbyte-python-cdk[dev]' --help

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[github-actions]

PyTest Results (Fast)

3 698 tests  +2   3 687 ✅ +2   6m 33s ⏱️ +4s
    1 suites ±0      11 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 9ee38c1. ± Comparison against base commit 1c9049a.