chore: add changeset for the env_local default stamp

Part of #13366

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D47qPfEWVPmhguWgBZCi5N

Author: claude

.changeset/standalone-stack-stamps-env-local.md

@@ -0,0 +1,38 @@
+---
+"@objectstack/runtime": patch
+"@objectstack/metadata": patch
+---
+
+fix(runtime,metadata): the default local environment id is `env_local`, not `proj_local` (#13366)
+
+The v5.0 `project` to `environment` rename changed the default local environment
+id and shipped that change on the surfaces most people meet: `packages/cli`'s
+`CHANGELOG.md` records "Default local env id: `proj_local` -> `env_local`", the
+`os dev` / `os start` / `os serve` commands emit `env_local`, and
+`content/docs/deployment/cli.mdx` documents `env_local` as the default. Two
+sites never received it and kept stamping `proj_local`.
+
+FROM: `createStandaloneStack()` — with no `environmentId` in its config and no
+`OS_ENVIRONMENT_ID` in the environment — stamped `proj_local` on the kernel it
+composed, and `MetadataPlugin` used `proj_local` to fill the environment-artifact
+validation envelope for a bare definition.
+
+TO: both stamp `env_local`.
+
+WHO SEES IT. Only a host that calls `createStandaloneStack` (or
+`createDefaultHostConfig`) **directly** and lets the id default. A boot started
+by `os dev` / `os start` never reached the changed line: those commands export
+`OS_ENVIRONMENT_ID=env_local` into the child process, which the fallback yields
+to. Where the id is observable — row scoping in `ObjectQLPlugin`, the
+`X-Environment-Id` header, `sys_metadata.environment_id` — such an embedder now
+sees `env_local` where it saw `proj_local`, so an install with rows already
+written under the old id should set `environmentId: 'proj_local'` (or
+`OS_ENVIRONMENT_ID=proj_local`) explicitly to keep them addressed. That escape
+hatch is unchanged and still wins over the default.
+
+NOT CHANGED, deliberately: `@objectstack/cloud-connection` still treats BOTH
+spellings as the local sentinel, so a persisted `OS_ENVIRONMENT_ID=proj_local`
+config keeps being recognised as local rather than presented to the control
+plane as a cloud environment id; and `package-state-store`'s separate `'default'`
+fallback keeps its own spelling, because renaming it would re-key persisted
+package-disable state files.