test(feed): bind fixtures to artifact runtime

[kachofugetsu09]

Summary

• make the manager integration fixture consume the explicitly supplied artifact Python
• derive the staged service runtime from AKASHIC_PLUGIN_FIXTURE_PYTHON instead of the pytest interpreter
• resolve the required environment boundary before any fixture copy, replacement, or removal
• bind GitHub Actions to the absolute artifact Python created by the preceding venv stage
• run the three MCP module behavior probes inside the artifact interpreter and return fixed JSON observations

Orthogonal boundary

• Core pytest owns the test process and assertions
• AKASHIC_PLUGIN_FIXTURE_PYTHON owns the service artifact runtime
• artifact probes remove inherited Core PYTHONPATH instead of adding artifact MCP to it
• missing fixture runtime and missing interpreter fail loudly
• no fallback, skip, mock success, or production compatibility path was added

Artifact MCP oracles

• recording FastMCP exposes only feed_manage and feed_query
• recording backend access returns the expected RuntimeError type and message
• runner logging creates one 5 MiB RotatingFileHandler with three retained generations

Validation

• 54 Feed tests passed
• MCP artifact probes: 5 passed
• manager integration: 4 passed
• Pyright: 0 errors and 0 warnings
• exact Plugin API v3 contract passed
• compileall and git diff --check passed
• workflow YAML parsed successfully and proved the venv stage precedes pytest
• workflow env equals the absolute GitHub workspace artifact path
• exact head a92a78e received independent Terra xhigh APPROVE with no P0 or P1 findings

Recovery

Pre-fixture bundle: /mnt/data/coding/backups/feed-fixture-python-env-20260824/pre-change-eec005f.bundle

Pre-MCP-probe bundle: /mnt/data/coding/backups/feed-fixture-python-env-20260824/pre-mcp-probe-24470a4.bundle

Pre-MCP-probe bundle SHA-256: 3aa651625a0e8222633c87eacf6979088faed1ac5313837e7dc2edeb31da1ff0

This stacked draft targets the head branch of Feed PR #6. It does not deploy or modify the formal hua-home workspace or plugin cache.