feat: add Python logging integration with structured events

[dgenio]

Summary

Add stdlib logging integration across all four subsystems (context, routing, store, adapters) with structured log messages. Zero runtime dependencies added — uses Python's built-in logging module only.

Fixes #111

Changes

• Context pipeline (context/): DEBUG logs for each pipeline stage — generate_candidates, dependency_closure, sensitivity_filter, apply_firewall, score_candidates, deduplicate_candidates, select_and_pack; INFO log for build completion with phase, included/dropped counts, and token usage
• Routing (routing/router.py): INFO log for route completion with top-k count, candidate count, and top-5 scores
• Store (store/): DEBUG logs for EventLog.append, ArtifactStore.put, EpisodicStore.add/search, FactStore.put
• Adapters (adapters/): DEBUG logs for MCP and A2A conversion functions
• Sensitivity guard: sensitivity_filter never logs text content — only action, floor level, and pass/drop counts
• Performance: All log calls use lazy %s formatting — zero cost at the default WARNING level
• Logger hierarchy: contextweaver.context, contextweaver.routing, contextweaver.store, contextweaver.adapters
• Tests: New tests/test_logging.py with 16 tests covering logger existence, INFO/DEBUG emission, and the sensitivity guard
• Docs: Updated AGENTS.md and .claude/CLAUDE.md debugging tips; updated CHANGELOG.md

Checklist

• Tests added or updated for every new/changed public function
• make ci passes locally (fmt + lint + type + test + example + demo)
• CHANGELOG.md updated under ## [Unreleased]
• Docstrings added for all new public APIs (Google-style)
• Every modified module stays ≤ 300 lines (or a decomposition issue is linked above)
• Related issue linked in the summary above
• Agent-facing docs updated if pipeline, API, or conventions changed

Notes for reviewers

• Sensitivity guard (context/sensitivity.py): The sensitivity filter deliberately logs only the action, floor level, and pass/drop counts — never the text content of items. This preserves the security-grade invariant.
• Zero cost at default level: All log calls use logger.debug("...", arg1, arg2) lazy formatting, so string interpolation is skipped entirely when the logger is at the default WARNING level.
• No new dependencies: Uses only import logging from the standard library.
• All 535 tests pass, including 16 new logging-specific tests.

[Copilot]

Pull request overview

This PR adds Python standard library logging integration across all four contextweaver subsystems — context pipeline, routing, store, and adapters — to address the lack of runtime observability (issue #111). It uses lazy %s formatting for zero string-interpolation cost at the default WARNING level, and the sensitivity module deliberately logs only structural metadata (never text content).

Changes:

• Added DEBUG-level log messages at each of the 8 context pipeline stages, store operations, and adapter conversions, plus INFO-level summaries for context builds and route completions
• Added 15 new tests in tests/test_logging.py covering logger existence, emission at correct levels, and the sensitivity guard (no text content in logs)
• Updated AGENTS.md, .claude/CLAUDE.md, and CHANGELOG.md with debugging tips and release notes

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/contextweaver/context/manager.py	DEBUG logs for ingest, ingest_tool_result; INFO log for build completion
src/contextweaver/context/candidates.py	DEBUG logs for generate_candidates and dependency_closure
src/contextweaver/context/scoring.py	DEBUG log for score_candidates with top/bottom scores
src/contextweaver/context/dedup.py	DEBUG log for deduplicate_candidates
src/contextweaver/context/selection.py	DEBUG log for select_and_pack
src/contextweaver/context/sensitivity.py	DEBUG log for sensitivity filter (action, floor, counts only)
src/contextweaver/context/firewall.py	DEBUG logs for single-item and batch firewall
src/contextweaver/routing/router.py	INFO log for route completion with scores
src/contextweaver/store/event_log.py	DEBUG log for append
src/contextweaver/store/artifacts.py	DEBUG log for put
src/contextweaver/store/episodic.py	DEBUG logs for add and search
src/contextweaver/store/facts.py	DEBUG log for put
src/contextweaver/adapters/mcp.py	DEBUG logs for mcp_tool_to_selectable and mcp_result_to_envelope
src/contextweaver/adapters/a2a.py	DEBUG logs for a2a_agent_to_selectable and a2a_result_to_envelope
tests/test_logging.py	15 new tests for logging across all subsystems
CHANGELOG.md	Unreleased entry for logging integration
AGENTS.md	Debugging tips for enabling subsystem loggers
.claude/CLAUDE.md	Debugging tips (mirrored from AGENTS.md)

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