Feature: opt-in global-basename wikilink resolution for Obsidian-convention vaults #972

Problem

When gbrain extract links ingests [[wikilinks]] from markdown files, the resolver only matches by:

1. Parallel directory + same basename (e.g., a link from originals/foo.md resolves [[bar]] to originals/bar.md)
2. Same directory + sibling basename (e.g., a link from concepts/foo.md resolves [[bar]] to concepts/bar.md)

It does not do a global-basename lookup. So a wikilink like [[struktura]] written in concepts/knowledge-graph.md does not resolve to projects/struktura.md, even though that page exists, has a unique basename in the vault, and resolves correctly in Obsidian.

This silently drops cross-directory bare-basename wikilinks. They're not flagged as broken — they're just missing from gbrain's graph layer.

Repro

# Set up a minimal vault with cross-directory link
mkdir -p /tmp/vault/{concepts,projects}
cat > /tmp/vault/projects/struktura.md <<EOF
---
title: Struktura
type: project
---
A project page.
EOF
cat > /tmp/vault/concepts/knowledge-graph.md <<EOF
---
title: Knowledge Graph
type: concept
---
This concept relates to [[struktura]].
EOF

gbrain init --force --dir /tmp/test-brain
GBRAIN_HOME=/tmp/test-brain gbrain import /tmp/vault
GBRAIN_HOME=/tmp/test-brain gbrain extract links
GBRAIN_HOME=/tmp/test-brain gbrain stats
# Links: 0 (expected: 1)

Obsidian's graph view correctly links the two nodes. Gbrain's graph layer does not.

Why it matters

For users who follow Obsidian's standard convention (flat-namespace wikilinks, globally-unique basenames), this silently drops most of their interlinking from gbrain's graph layer. We hit this on a fresh wiki: 71 wikilinks total across 20 pages in Obsidian (avg 3.55/page, dense galaxy), but gbrain's extract links only produced 12 — all of which were same-directory. The remaining ~60 cross-directory bare-basename links were dropped silently.

Symptoms downstream:

• gbrain graph <slug> returns thin or missing edges that exist in the source files
• gbrain backlinks <slug> undercounts incoming references
• Graph-traversal queries (e.g., "what concepts touch this project") return incomplete neighbors
• Semantic search via gbrain query is unaffected (works on chunks/embeddings, not the graph layer) — but anyone relying on graph traversal gets a partial view

Why it's probably intentional (and what to do anyway)

Gbrain's parent/ancestor resolution suggests it's designed for monorepo-style knowledge bases where basename collisions across folders are common, and path disambiguation is necessary. That's a defensible design choice for one user population. But Obsidian convention is the opposite — flat namespace, globally-unique basenames, bare wikilinks everywhere. The two assumptions clash.

Proposed: add an opt-in "global basename" resolution mode

# gbrain.yml or config
link_resolution:
  mode: ancestor          # current default — backward compatible
  # OR
  mode: global_basename   # treat bare wikilinks as referring to any uniquely-named page in the vault

In global_basename mode, resolveSlug("struktura", from_page) would:

1. Try parent/ancestor lookup first (current behavior)
2. Fall back to: search allSlugs for any slug whose basename matches
3. If exactly one match → resolve to it
4. If multiple matches → ambiguous, drop with a warning (so the user knows to disambiguate via path prefix)
5. If zero matches → drop silently (existing behavior)

Default stays ancestor for back-compat. Users with flat-namespace vaults flip to global_basename in their config.

Alternative — auto-detect from gbrain doctor

gbrain doctor could count bare-basename wikilinks that fail to resolve under ancestor mode but WOULD resolve under global mode, and surface that as a hint:

ℹ️  Detected 60 wikilinks that would resolve under global_basename mode but currently drop.
   Your vault appears to use Obsidian-flat-namespace convention.
   Set `link_resolution.mode: global_basename` in gbrain.yml to enable.

Severity

Medium. Doesn't break anything (semantic search works fine), but silently undercounts the graph for Obsidian-convention users, leading to thin/wrong graph traversal results. Easy upstream fix; current workarounds (path-prefixed wikilinks everywhere) are ugly enough that most users would rather accept the gap than adopt them.

Affected file

src/core/link-extraction.ts — the resolveSlug function around line 160-192.

Diagnosed by an agent

This was caught by an LLM agent (Hermes-driven Echo) doing read-after-write verification on a freshly-seeded wiki, then reading gbrain's source to confirm the resolver mechanism. Worth noting as evidence that the verify-before-done discipline catches real architectural gaps that wouldn't show up in CLI smoke tests.