fix(buck2): export consumer TypeScript runner

[schickling-assistant]

Problem

The standalone Buck rules artifact copied the provider workspace's root BUCK file even though that file referenced targets and packages that the artifact intentionally omits. The artifact also did not own the root targets expected by mkConsumerBuckRoot. A standalone consumer therefore failed while analyzing the configured TypeScript toolchain with package .../buck2-tools does not exist.

Goal

Give the distributed rules artifact a self-contained root package that exposes only its declared runtime surface.

Decisions

• Generate a minimal artifact-owned root BUCK package during the Nix build.
• Define package_tree_runtime, package_command_runtime, and the nested TypeScript runner export in that package.
• Stop copying the provider workspace root BUCK file into the artifact.
• Extend the consumer-root contract test to query all three root targets and analyze the configured TypeScript toolchain.

Verification

• Replayed the previously failing consumer root with the new minimal rules BUCK package.
• buck2 cquery fixture//buck2/toolchains:effect_tsgo succeeds.
• buck2 uquery resolves rules//:package_tree_runtime, rules//:package_command_runtime, and rules//:packages/@overeng/buck2-tools/src/typescript-runner.ts.
• The generated inventory source and committed projection match.
• git diff --check passes.

Pre-flip deviations

devenv tasks run check:quick --no-tui remains queued behind the shared heavy-build admission outage tracked in schickling/dotfiles#2984. The focused replay above exercises the exact analysis failure and the final artifact contract.

Complexity

Low. The distributed artifact now owns a three-target root package instead of importing an unrelated workspace root.

Concerns

None.

Friction & bottlenecks

The shared heavy-build admission lock is held beyond its runtime cap. That outage prevents the repository-wide gate from starting.

Follow-ups

None.

References

• Regression introduced with schickling assistant/2026 09 20 p2 rules product #1324
• Shared validation outage: schickling/dotfiles#2984

Posted on behalf of @schickling

field	value
agent_identity	dev3.direct.omp.mqs8cse3
session	unknown
agent_persona	generalist
agent_supervisor	unavailable
agent_tool	OMP
agent_tool_version	18.2.6
agent_runtime	OMP 18.2.6
agent_model	openai-codex/gpt-5.6-sol
worktree	effect-utils/2026-09-20-p2-rules-product
tooling_profile	dotfiles@965ef7e-dirty