chore: Sync from internal → open source (2026-08-19) — step 1/2 (pre-pin)

[setu4993]

Automated sync from the internal repo, up to `bca2e7c0` (the commit before the AgentFabric workspace-dep pin, internal #569).

Why this is step 1 of 2

The internal repo later pinned `dialect/agentfabric`'s deps to exact versions (`@agentscript/agentscript-dialect@2.23.0`, `@agentscript/language@2.20.0`, `@agentscript/parser@4.0.7`). A single full sync would ship those pins before the referenced versions exist on public npm, so `pnpm install --frozen-lockfile` 404s in CI.

Splitting the sync:

1. This PR — everything up to just before the pin. AgentFabric deps are still `workspace:*` (pin-free), and the packages here are at exactly `agentscript-dialect@2.23.0 / language@2.20.0 / parser@4.0.7`. Merging + releasing this publishes those versions to public npm.
2. Step 2 (later) — the remainder up to internal master tip, including the pin. Once step 1 is released, the pinned versions resolve normally and CI passes.

Merge order matters: merge and release this PR before step 2 is exported.

Review

• Single, human-authored squashed commit.
• gitleaks + all 7 red-line checks pass; build/test green (24/24 tasks).
• Excludes the pre-#606 duplicate `packages/compiler/generated/` dir (an older layout present at this commit) so the internal-only `transitions` schema is not published.