[azmi2409]

Issue number: closes #8695

Summary

Changes

• In _parse_and_validate_event, when validate_json rejects a string payload with a ValidationError, fall back to validate_python on the raw value instead of failing immediately. If Python validation also fails, the original JSON error is re-raised, so genuinely invalid payloads still surface the same error as before.
• This fixes the shared string-parsing path, so it applies to every envelope that parses string payloads, not only CloudWatch Logs.
• Added three regression tests in test_cloudwatch.py: plain-text Lambda runtime messages (START/END/REPORT plus an INFO line) are returned as-is with model=str, mixed JSON and plain-text messages are returned as-is with model=str, and plain text still raises ValidationError for an object model.

User experience

Before: parsing a real CloudWatch Logs subscription event with CloudWatchLogsEnvelope and model=str raised a ValidationError as soon as any log event was a plain-text Lambda runtime message (START, END, REPORT), even though the user asked for strings.

After: those plain-text messages are returned as-is alongside JSON messages, JSON messages for object models still parse as before, and plain text for an object model still raises a ValidationError.

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[leandrodamascena]

Thanks @azmi2409, confirmed with real Lambda runtime lines from one of our functions: START, END and REPORT now come back as strings with model=str, a JSON line next to them still parses, and a plain line against an object model still fails with the same json_invalid as before. Since this touches the shared string path I ran the other envelopes and parse() directly too. Two things change beyond the issue, both for the better: model=str with a JSON object payload now returns the string instead of failing, and bare ISO dates parse for model=datetime. I'll mention them in the release notes.

I'm approving now. This goes out in 3.40.0, so it will sit here for a while before I merge it. No rebase needed in the meantime, and you'll be credited in the release notes.

[leandrodamascena]

Re-approving after a small refactor on top: the nested fallback pushed parser/functions.py over the module complexity rank xenon enforces in CI, so I moved the string handling into _parse_string_payload. Same behaviour, 222 parser tests pass.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.01%. Comparing base (8b5ec90) to head (5eb80f2).

Files with missing lines	Patch %	Lines
...ws_lambda_powertools/utilities/parser/functions.py	84.61%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8699   +/-   ##
========================================
  Coverage    97.01%   97.01%           
========================================
  Files          321      321           
  Lines        16424    16431    +7     
  Branches      1484     1484           
========================================
+ Hits         15933    15940    +7     
  Misses         350      350           
  Partials       141      141           

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