Stream large workflow history exports

[MacHatter1]

Summary

• Stream large bb workflows history <run-id> exports without truncation.
• Preserve the buffered 1 MiB safety limit and explicit --cursor/--limit compatibility.
• Make stream cancellation, plugin reload, and candidate activation rollback resource-safe.

Problem

Valid workflow history output could exceed the buffered plugin CLI response limit. A real dev-app run produced a valid 1,049,375-byte JSONL export and exited successfully on the streaming path, while packaged BB 0.40.0 rejected the same boundary as plugin_cli_output_too_large.

Implementation

• Adds an experimental streamed stdout result to the plugin CLI boundary.
• Streams plugin output through the server and CLI with backpressure, cancellation, and 64 KiB UTF-8 chunks.
• Makes default Workflows history follow all pages automatically; explicit cursor/limit requests remain single-page compatibility behavior.
• Keeps buffered stdout/stderr bounded at 1 MiB.
• Protects plugin reload from active streams, failed candidate activation, schedule persistence failures, and pending iterator cancellation.
• Updates API inventory, authoring guidance, Workflows documentation, and regression coverage.

Validation

• Workflows tests: 228 passed.
• Focused CLI tests: 36 passed.
• Focused server/plugin tests: 42 passed.
• Plugin API-map checks: 4 passed.
• Affected Turbo typechecks and builds passed.
• git diff --check passed.
• Live dev-app verification confirmed a JSONL export larger than 1 MiB is lossless and parseable.

No host-daemon protocol change is included.