Complete the public type surface and narrow closed-union output fields

[jantimon]

What

Two additive / output-narrowing changes to the public type surface (src/index.ts), shipping as a minor. No runtime behaviour changes.

1. Export the transitively-referenced fact types

The AGENTS.md promise is "import them, do not hand-roll": every type named inside an exported type should itself be importable. It was not. This re-exports the full transitive closure from the package root:

• Core barrel: CaptureMode, TargetLane, WorkloadLane, WorkloadIdentity, Measured, CpuBreakdown/CpuSlice/CpuJsSlice, LayoutShift(+Source/Rect), EngineSoftNav, SoftNavRoute(+Lcp), ThrashReport/ThrashStep/DirtiedByWrite/DirtiedByWriteRollup/FirefoxDirtiedByReport, SourceMapDiagnostics/SourceMapFailure.
• View homes: SpanCountsEntry (query), SoftNavVerdict/SoftNavAgreement (soft-nav), FrameFloorMatch (frame-floor).
• Raw profile: RawProfileNode/RawCallFrame/GeckoSlice.
• Driver: StepOpts/Until (StepOpts gains export).

Eight of these (Measured, WorkloadLane, SoftNavAgreement, RawProfileNode, RawCallFrame, GeckoSlice, StepOpts, Until) were surfaced by the guard test below beyond the initial list.

2. Narrow the closed-union output fields off string

• RecordingMeta.capture and GroupSpanMember.mode -> the CaptureMode union, extended in record/capture.ts with the node-cpu/node-alloc node lanes (no precise-wall arm; the schema-5 epoch gate rejects any pre-5 recording that could carry it).
• SpansResult.target / SpanAnatomy.target / GroupSpanStitch.target -> "chrome" | "firefox" | "node" (a new TargetLane, now the return type of recordingLane).

Reading these fields now yields the exact literal type instead of a bare string. The spec-open fields (LoafScript.invokerType, EngineSoftNav.navigationTypes, SoftNavRoute.navigationType, meta.target) are deliberately left as string.

RecordingMeta gains a doc note that it carries no kind discriminant (the field GroupMeta stamps "run-group" to mark the sibling manifest).

3. Guard test

test/unit/export-completeness.test.mjs walks the emitted dist/*.d.ts with the TypeScript compiler API and fails if any type reachable from a public export is not itself exported. Browser-free, no new dependency (uses the TypeScript already used to build). This is what a dropped or forgotten re-export trips on, instead of a consumer's red build.

Notes

• The GroupSpanMember.mode narrowing needs a boundary cast (member.mode as CaptureMode): the run-group manifest's GroupMember.mode stays the wider string (out of scope here), but its value is the member recording's meta.capture verbatim, which is now a CaptureMode.
• Model files take a type-only import { CaptureMode } from record/capture.ts; it erases in emit (verified: no runtime require in dist/model/meta.js), so there is no runtime cycle.

Gates

build, lint, format:check, knip, unit (686 tests, incl. the new guard), e2e (Chrome), and measurement all pass.