Delete the workspace file read

[SaladDay]

workspace_read carried two operations: a byte-file read and a directory listing. Core never requests a file read: runtimegateway.Session.ReadWorkspaceFile had no caller outside tests, and only ListWorkspaceDirectory is called (from execution/environment_directory.go). Every daemon path serving a file read was unreachable.

Deleted end to end (about 860 lines net):

• Wire: max_bytes, operation, data and truncated, and WorkspaceReadMaxBytes. operation was always directory once the file form is gone. proto.Version stays 0.12.0.
• Core: ReadWorkspaceFile, with one result validator left.
• Daemon: dispatch's reader branch; agent.WorkspaceReader and WorkspaceReadResult; localworkspace ReadWorkspaceFile; the Claude SDK read path (Go side, stdin frame, TS workspace_reads.ts, the workspace_read runtime feature); the Codex and MiniMax Code stubs.
• Selection: workspaceResourceLocked returns a WorkspaceDirectoryLister instead of any. A preparation handle is served only by the local workspace binding (the only producer of a read-only preparation); the dead p.prepared / p.executor.native selection is gone.

Directory listing is unchanged, and workspace_read keeps its name. Docs: docs/runtime-protocol.md and harness-onboarding.md (+ zh).

Checks:

• Go: focused tests for runtimegateway, execution, dispatch, localworkspace, agent, cli and proto; -race -count=50 on the changed concurrent tests; vet and gofmt; darwin/windows daemon builds.
• Core integration: 49 tests that touch workspace reads, against Postgres.
• Claude SDK adapter: pnpm typecheck and node --test (160/160).
• Repo checks: the translations test and make check-names check-docs check-ci.

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