Plugin: graph view + backlinks / unlinked mentions (#71)

[thetechjon]

Why a plugin, not a core component

The brief asked for two complementary surfaces — a backlinks /
unlinked-mentions sidebar panel and a force-directed global graph
view — and Jon's standing rule is "build new feature surfaces as
plugins where the Plugin API can carry them." v1.2 (PRs A, B, C, F
plus the post-v1.2 VNode event delivery + wikilink intercept
follow-up in #142) added every capability this work needs:

• vault.read.all for body access across the whole vault (PR C).
• vault.events for debounced re-derivation on save and on
  active-note change (PR F).
• fullscreenViews surface for the global graph (PR B).
• The full v1.2 VNode set including svg, link, button, box,
  and list (PR A).
• ctx.onVNodeEvent plus the wikilink:// click intercept (Wire VNode event delivery + wikilink intercept (post-v1.2 followup) #142),
  without which the SVG and the per-link backlinks list would be
  inert.

Building this as core today would re-introduce the gap v1.2 was
supposed to close. Shipping it as the reference plugin for this
capability set instead validates the API surface end-to-end and
gives the next plugin author a working blueprint.

What this PR changes

Two new directories, four new files:

public/plugins/noteser-graph/manifest.json       (25 lines)
public/plugins/noteser-graph/main.js             (~950 lines)
public/plugins/noteser-graph/README.md           (~160 lines)
src/__tests__/noteserGraphPlugin.test.ts         (~380 lines, 35 cases)

No core source changes. The existing
src/components/sidebar/BacklinksView.tsx and
src/utils/backlinks.ts stay in place; the swap plan is documented
in public/plugins/noteser-graph/README.md under "Co-existence
with core BacklinksView".

Surfaces shipped

Sidebar panel Graph (active note):

• Backlinks: notes whose body contains a wikilink to this note's
  title (case-insensitive).
• Unlinked mentions: whole-word title matches that are NOT inside
  an existing [[wikilink]], NOT inside a fenced code block, and
  NOT inside an inline code span.
• "Open global graph" button at the bottom.

Fullscreen view Graph: hand-rolled force-directed SVG of the
whole vault. Adaptive iteration schedule keeps 1 k nodes under the
500 ms budget without Barnes-Hut. Header buttons cover Recompute,
Reset view, Zoom in / out, and four-direction Pan.

Performance numbers (measured on the worktree)

Operation	Vault size	Time	Budget
Panel re-derive on note switch	5 000 notes	~23 ms	<50 ms
Graph derive + layout	1 000 nodes / 3 000 edges	~400 ms total (derive ~6 ms + simulate ~400 ms)	<500 ms

The plugin emits console.log lines for both numbers so the
budget is verifiable on any real vault from the devtools console.

Deprecation plan for core BacklinksView

Documented in detail in the plugin's README.md. Three steps:

1. Default-install the plugin so a brand-new vault has both
   surfaces.
2. Port alias support across. The core view honours
   getAliasesForNote(note) from src/utils/aliases.ts; the
   plugin currently matches title only. NoteWithBody.frontmatter
   already exposes parsed frontmatter, so the alias scanner only
   needs to be re-implemented inside the plugin.
3. Delete src/components/sidebar/BacklinksView.tsx and its
   right-sidebar registry entry. The internal
   src/utils/backlinks.ts helper stays for the sync layer's
   broken-link check.

v1.2 API gaps surfaced

Three pieces of the brief did NOT map cleanly to the v1.2 VNode
event set, so the plugin ships button-based equivalents and a
two-click open path. Both are called out in the plugin's README:

• Wheel = zoom: no onWheel on VNodes. Shipped as Zoom in /
  out buttons.
• Drag = pan: no onPointerDown / onMouseMove on VNodes.
  Shipped as four-direction Pan buttons.
• Click a circle opens the note in one click: SVG children
  accept onClick only (no link-wrapping in the SvgChild union),
  and PluginCtx has no ctx.openNote(id) method. Shipped as
  two-click: click circle to select, then click the link VNode
  the plugin renders in the header to navigate (the host's
  wikilink:// intercept fires on that click).

A v1.3 increment that adds onWheel + pointer events on SVG and a
ctx.openNote(id) method would close all three without breaking
this plugin's UI. Not blocking the merge.

Test plan

• npm run lint clean.
• npx tsc --noEmit zero errors.
• npm test -- --ci green (208 suites, 2 599 tests pass; 1
  skipped suite is unrelated).
• New tests at src/__tests__/noteserGraphPlugin.test.ts
  cover the unlinked-mention detector (code-block exclusion,
  inline-code exclusion, wikilink exclusion, whole-word
  matching, multi-word titles, case-insensitivity), graph
  derivation on a 5-note fixture (self-link drop, parallel-
  edge de-dup, untitled-source handling, degree counting,
  orphan handling), the snapshot-SHA cache key, and the
  force simulator's determinism + bounds.
• Manual smoke: run npm run dev, paste
  http://localhost:3001/plugins/noteser-graph/manifest.json
  into Settings -> Plugins, grant vault.read.all +
  vault.events, open a note with wikilinks, verify the
  panel shows backlinks; click "Open global graph", verify
  the SVG renders, the zoom / pan buttons work, and clicking
  a node followed by clicking the resulting link row opens
  that note.

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