Decompose inputs/n8n.py into inputs/n8n/ package (v0.21 E8)

[pengfei-threemoonslab]

Summary

Closes round-3 architecture-review evolution item E8. The largest input adapter was 1493 lines monolithic — out of line with the typical adapter file (mcp.py 148, openapi.py 343, langchain.py 305) and flagged as a structural-debt item for four consecutive review rounds.

The file is now a 6-module package under src/agents_shipgate/inputs/n8n/ with per-concern boundaries.

New layout

Module	LOC	Concern
__init__.py	54	Re-export public surface (N8nAdapter, load_n8n_artifacts)
_common.py	300	Constants, _NodeItem/_Edge, leaf helpers, node-kind classification
_secrets.py	122	Secret scanning against v0.19 global SECRET_PATTERNS
_auth_risk.py	148	Credentials, AuthInfo, risk-hint heuristics, HTTP path hint
_tools.py	492	Tool extraction for 5 flavours + projected mcp + schemas + MCP selection
_workflows.py	464	File loading, shape detection, _extract_workflow, edges, record builders
_adapter.py	249	N8nAdapter, load_n8n_artifacts, auxiliary loaders

Largest sub-module is _tools.py at 492 lines — still under the typical largest-adapter threshold, and far below the original 1493.

Dependency direction (DAG at module-load)

_common  ←  _secrets, _auth_risk  ←  _tools  ←  _workflows  ←  _adapter

_tools calls back into _workflows (for record builders and dynamic-surface emission) via late imports inside the call sites that need them. This is the inherent shape of the n8n pipeline — workflows own "what is a node," tools own "what is a Tool emitted from a node" — and the late-import scoping keeps the static import graph one-way.

Public surface preserved

from agents_shipgate.inputs.n8n import N8nAdapter        # used by inputs/protocol.py
from agents_shipgate.inputs.n8n import load_n8n_artifacts # used by tests/test_n8n.py

Both external import sites keep working unchanged via __init__.py re-exports. No behavior change.

One adjacent contract-test fix

tests/test_public_surface_contract.py::test_supported_inputs_match_adapter_class_vars_bidirectionally walked adapter_dir.glob(\"*.py\") looking for the source_type ClassVar literal. That pattern was written when n8n was a single file; with n8n now a sub-package the literal lives at inputs/n8n/_adapter.py. Switched to rglob(\"*.py\") with a __pycache__ guard. Same coverage, sub-package support included.

Test plan

• tests/test_n8n.py: 30/30 pass byte-identical (no behavior change).
• tests/test_adapter_static_only.py: 216/216 pass — new sub-modules scanned by v0.18 trust-lint and clean.
• tests/test_fixture_no_import.py::test_n8n_adapter_does_not_import_sibling_python: pass.
• tests/test_adapter_entry_point_discovery.py: 36/36 pass — N8nAdapter remains discoverable through the registry.
• tests/test_public_surface_contract.py: full pass after the rglob fix.
• python scripts/generate_schemas.py --check: clean.
• ruff check .: clean.
• Full pytest suite: pass; coverage 88.13% (above 75% floor).

File-size delta

• Old: 1493 LOC monolithic
• New: 1829 LOC across 7 files
• Net: +336 LOC from per-module docstrings, import groupings, and the re-export header — the inherent cost of decomposition. The cognitive-load reduction is in per-file size, not aggregate.

Stability

• No report_schema_version bump (catalog-internal change).
• No public Python API change.
• No CLI flag change.
• STABILITY.md unchanged.

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