fix(context): always return inner dict from process_sources

[0xghost42]

Summary

SourceProcessor.process_sources is invoked with a SearchResult from serp_search.get_sources and its return value is fed straight into build_context, which reads .get('organic') / .get('topStories') / .get('answerBox') on a plain dict (context_building/build_context.py:55-90).

Three of the four return paths inside process_sources already unwrap the inner dict:

return sources.data
return self._update_sources_with_content(sources.data, valid_sources, html_contents, query)

The other two leak the SearchResult wrapper:

if not valid_sources:
    return sources                 # <-- SearchResult
except Exception as e:
    ...
    return sources                 # <-- SearchResult

Whenever the SERP call returns no organic results (empty query, rate limiting, quota exhaustion, etc.) or the scrape/rerank step raises, build_context then crashes with:

AttributeError: 'SearchResult' object has no attribute 'get'

This is the same error surfaced in #15. The reporter's root cause turned out to be an install issue (No module named 'src') that ended up in the except branch, but the underlying inconsistency is real — any future exception inside process_sources will surface as the same misleading AttributeError downstream rather than being logged and recovered.

Change

src/opendeepsearch/context_building/process_sources_pro.py:

• Unwrap sources.data in both leaking branches, falling back to {} when data is None (the error-result case — SearchResult.__init__ leaves data=None when constructed with error=...).
• build_context already tolerates an empty dict (its extract_information(sources_result.get('organic', [])) chain returns '' cleanly), so the agent now degrades gracefully instead of crashing.
• Return annotation updated from List[dict] to dict to match the actual contract. sources parameter annotation dropped — it was typed List[dict] but is in fact a SearchResult, and importing SearchResult into this module just for the hint is more churn than the fix warrants.

Verification

• python -m py_compile src/opendeepsearch/context_building/process_sources_pro.py clean.
• Traced both leaking paths to build_context and confirmed they previously triggered AttributeError: 'SearchResult' object has no attribute 'get'; after the fix, build_context receives {} and returns ''.
• The three already-correct paths (return sources.data, return sources.data via wiki branch, return self._update_sources_with_content(sources.data, ...)) are unchanged.

Out of scope

The wider type-annotation mismatch (_get_valid_sources / _update_sources_with_content declare List[dict] but operate on the inner SERP dict) is left for a separate cleanup PR — the runtime bug is what this PR addresses.