fix: report empty connections targets instead of crashing the render

[Itachi3355]

Fixes #2865

Problem

An empty or whitespace-only value in connections reached selectOne as a selector, where css-what threw:

error: Expected name, found .
  at getName (node_modules/css-what/lib/commonjs/parse.js:95:23)
  at resolveImplicitSinglePort (lib/components/primitive-components/Trace/Trace__findConnectedPorts.ts:29:47)

Two problems, as described in the issue:

1. The exception aborted the entire render, so one bad entry produced no circuit JSON at all — sibling connections, other components and every downstream phase never ran.
2. The message named neither the component nor the pin, and pointed at css-what internals. The natural reading is that the valid selector is malformed.

Fix

Empty targets are skipped when collecting nets (_getNetsFromConnectionsProp) and when creating traces (_createTracesFromConnectionsProp), so the rest of the board renders. The misconfiguration is recorded as a source_component_misconfigured_error naming the component and pin:

<capacitor#13 name=".C1" /> has an empty connections target for pin "pin1". Provide a selector such as ".R1 > .pin1" or "net.VCC", or remove the entry.

The error is emitted in doInitialSourceComponentPropertyValidation rather than at trace-creation time, because CreateTracesFromProps runs before SourceRender and source_component_id does not exist yet.

Scope, following the issue author's notes:

• Only empty and whitespace-only targets are treated as misconfigured. A non-empty but unresolvable selector (".R9 > .pin1" where R9 doesn't exist) already has its own downstream handling and is untouched.
• The check covers both the string and array forms of a connections entry.
• Kept in core rather than rejecting "" at the props-schema level in tscircuit/props, which would be a cross-repo change with a wider blast radius.

Verification

• 2 new tests in tests/components/normal-components/empty-connections-target.test.tsx. Both fail on clean main with the exact reported Expected name, found . crash, and pass with the fix.
• Ran the 310 test files that reference connections: 308 pass / 4 fail. The same 4 fail on clean main with this change stashed — all autorouting/breakout/fanout, unrelated to this path. No failure is unique to this change.
• bunx tsc --noEmit exits 0; biome format clean.

One unrelated flake noticed while establishing the baseline: tests/features/autoroutingphase-connection-phase-index.test.tsx failed 2 of 3 runs on clean main with this change stashed.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
tscircuit-core-benchmarks	Ready	Preview	Sep 18, 2026 3:31pm UTC

[github-actions]

This PR has been automatically marked as stale because it has had no recent activity. It will be closed if no further activity occurs.

[Itachi3355]

Merged current main (33 commits) and re-verified — the two regression tests still pass, and there were no upstream changes to NormalComponent.ts, so no conflicts. CI is green.

Not stale from my side; this is waiting on maintainer review. Happy to rebase, split, or adjust the error message/wording if you would prefer a different shape.

🤖 Addressed by Claude Code