Mermaid output wiring ignores input-root output sources

[spinje]

Summary

_connect_sources_to_output in src/pflow/core/workflow/mermaid/_io.py only recognizes node IDs as output source roots. When an output source references a workflow input (e.g., source: ${data.field} where data is a declared input), the output node renders with no incoming edge — disconnected in the diagram.

Root cause

_io.py:195-197:

for src_node, field in _SOURCE_NODE_FIELD_RE.findall(source):
    if src_node not in node_ids:
        continue  # Input names are silently dropped

_SOURCE_NODE_FIELD_RE captures name.field patterns. When src_node is a workflow input name (not a node ID), it's filtered out. The output node has no edge connecting it to the input.

Additionally, bare input references (source: ${data} without a dot) don't even match the regex (requires name.field format), so they're also disconnected.

Reproducer

from pflow.core.workflow.mermaid import generate_mermaid

ir = {
    "ir_version": "0.1.0",
    "nodes": [{"id": "process", "type": "shell", "params": {"command": "echo ${data.field}"}}],
    "inputs": {"data": {"type": "dict", "description": "Input data"}},
    "outputs": {"result": {"source": "${data.field}"}},
}

print(generate_mermaid(ir))
# Output node "result" has no incoming edge — should connect from input "data"

Fix direction

In _connect_sources_to_output, when src_node not in node_ids, check if it's in the workflow inputs. If so, connect the output to the corresponding input parallelogram node instead of skipping.

Discovered during

Code review of GH #247 fix (validator now allows input-root output sources). The validator and runtime handle these correctly, but Mermaid rendering was never updated to match.