Fix multiline JSON extraction in exceptions helpers

[biefan]

Summary

This updates extract_json_from_string() to correctly extract multiline JSON payloads from larger strings.

Problem

extract_json_from_string() currently relies on a regex:

re.compile(r"\{.*\}|\[.*\]")

That has two problems for real model output:

1. . does not match newlines by default, so multiline JSON objects and arrays are not matched as a whole.
2. When the outer JSON spans multiple lines but contains a nested single-line object, the regex can skip the outer payload and return the nested fragment instead.

In practice, this means helper code can extract the wrong JSON fragment from valid responses that include explanatory text plus a pretty-printed JSON body.

Fix

Replace the regex-based extraction with json.JSONDecoder().raw_decode() scanning logic:

• scan for candidate { / [ starting positions
• attempt to decode a JSON object or array from each candidate position
• return the first complete decodable payload

This preserves existing behavior for single-line JSON while fixing multiline extraction and avoiding nested-fragment false matches.

Tests

Added a regression test covering a multiline JSON object embedded in surrounding text.

Validation command:

uv run --extra dev pytest tests/unit/exceptions/test_exceptions_helpers.py -q

Validation result:

31 passed in 0.04s

[Copilot]

Pull request overview

This PR improves JSON payload extraction from mixed model output strings by replacing a regex-based approach (which fails on multiline JSON and can select nested fragments) with a json.JSONDecoder().raw_decode() scan, and adds a regression test for the multiline/nested case.

Changes:

• Replace regex JSON extraction with incremental decoding via json.JSONDecoder().raw_decode().
• Ensure multiline JSON embedded in surrounding text is extracted correctly (and avoids nested-fragment false matches).
• Add a regression test for multiline object extraction.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pyrit/exceptions/exceptions_helpers.py	Reworks extract_json_from_string() to scan and decode JSON objects/arrays instead of using regex.
tests/unit/exceptions/test_exceptions_helpers.py	Adds a regression test covering multiline JSON with a nested single-line object.

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[rlundeen2]

Looks great, thanks for the PR @biefan!