fix(explain): render arrows in original edge direction (#853)

[spindle79]

Fixes #853.

Summary

Same structural bug as #849, same fix shape as PR #851 — applied to graphify explain. Previously every connection rendered as --> X [relation], asserting a backwards call graph whenever the queried node was a callee.

Reproducer

Real-world: explain validateSanitySession() printed --> createPatchHandler() [calls] even though the stored edge is createPatchHandler --calls--> validateSanitySession (verified in graph.json and by the file source). validateSanitySession() is a pure leaf utility — all 13 of its connections are inbound — yet every one rendered as outbound.

Fix

Same as #851:

• Force directed interpretation on read (_raw = {**_raw, "directed": True}) so the loaded G is a DiGraph preserving edge direction.
• Iterate G.successors(nid) and G.predecessors(nid) separately, tagging each connection as "out" or "in".
• Render --> for outbound, <-- for inbound.

A neighbor that has both an inbound and outbound edge to the queried node (mutual references) is rendered twice — once per edge. That's the truthful directed representation; the previous undirected G.neighbors() would have silently collapsed it to one row.

Tests

tests/test_explain_cli.py — two tests, both on a graph.json fixture whose on-disk shape matches what graphify update produces (directed: false, links[i].source = caller):

1. test_explain_renders_callers_as_inbound_and_callees_as_outbound — queried node is validateSanitySession. Its two callers (createPatchHandler, createEditHandler) must render as <--; its own callee (stableStringify) must render as -->. Asserts the old buggy --> createPatchHandler() [calls] is not in the output.
2. test_explain_renders_pure_caller_as_outbound — converse: querying createPatchHandler must show validateSanitySession as --> and no <-- rows.

The fixture writes graph.json directly rather than via nx.Graph().add_edge() + node_link_data() — the latter emits links in node-insertion order, not edge-argument order, which can silently encode the wrong direction in small fixtures and mask the bug.

Test plan

• Two new tests pass locally.
• Full suite: 737 passed, same 11 baseline failures (SQL needs optional tree-sitter-sql; one Fortran preprocessed test; two Ollama env-var tests) — zero new failures.
• Manual repro: explain validateSanitySession() now renders all 13 connections as <--. Verified on the same Sanity Studio plugin reproducer used in graphify path renders reversed arrows because graph is undirected (renderer bug, post-#760) #849/fix(path): render arrows in original edge direction (#849) #851.

Notes for the reviewer

• If fix(path): render arrows in original edge direction (#849) #851 has already merged, this branch may need a trivial rebase (both touch adjacent regions of __main__.py for path/explain), but the two changes are independent.
• The directed-on-read interpretation is safe even for graphs serialized with directed: false because links[].source/.target are preserved verbatim by node_link_graph and always represent caller→callee per the existing build conventions — verified empirically on real graphs.

[safishamsi]

Thanks for the report! We shipped this fix ourselves in commit 7bb0919 (v0.7.17) — explain arrow direction now correctly shows --> for successors and <-- for predecessors in directed graphs. Closing since the fix is already in main.