v1.12.0: per-task context

A run already plans on context from a brain (the ContextProvider seam). This routes that seam down to every task, so each agent in a parallel or looped plan gets fresh, task-specific context, not one snapshot taken once before planning.

• Per-task context: with a ContextProvider, the dispatcher pulls context(task.instruction) for each task before it runs, caps it (like upstream data), injects it into the task's prompt, witnesses it as a context entry, and chains the task to it, so the record shows exactly what context shaped each task. The default NullContextProvider returns nothing, so this is a no-op until a brain is plugged in, and Forum stands alone.
• Peer-composition holds: Forum times, routes, and witnesses (its lane); the brain assesses and supplies (its lane); the injected context is verified (witnessed) and fresh (pulled per task). Forum never generates it. The pull is synchronous per task, so a brain doing heavy I/O serializes the wave; it is meant to be fast and offline.

Pure standard library. 249 tests, plus 2 gated real-model tests.

Install: pip install forum-engine