refactor(core): centralize tool context runtime bindings

[limityan]

Summary

• Move ToolUseContext runtime/service bindings out of framework.rs into core-owned tool_context_runtime.rs.
• Keep framework.rs focused on context shape, portable facts projection, and the Tool trait.
• Centralize pipeline, manifest-description, and write-preflight ToolUseContext materialization in the same runtime binding owner.
• Preserve existing custom_data shape, same-key overwrite order, cancellation state, runtime restrictions, workspace services, and Deep Review parent-context propagation.
• Add boundary-script anchors so runtime coordination, workspace runtime lookup, path policy, context materialization, cancellation/post-call hooks, and checkpoint collection do not drift back into framework or execution internals.
• Update core decomposition docs and core AGENTS guidance to describe the current owner boundary accurately.

Behavior and Boundary Notes

This remains a structure-only runtime owner closure. It does not migrate ToolUseContext, runtime service handles, concrete tools, collapsed unlock state, GetToolSpecTool, product tool registry snapshots, or product feature/build assembly out of core.

The additional tool-related cleanup only moves remaining production context construction for prompt manifest description and write preflight into the same core-owned binding module. It preserves the current field values and insertion order, including the existing context_vars overwrite behavior for manifest description custom_data.

The latest rebase to gcwing/main completed without conflicts. The latest main-side change observed in this rebase does not affect the tool-runtime plan or document assumptions.

Regression Coverage

• remote workspace containment
• runtime URI workspace-scope validation
• path policy allow/block behavior
• tool-call cancellation hook behavior
• tool task context materialization, including existing custom_data keys and Deep Review parent metadata
• manifest-description context materialization shape
• write-preflight context materialization shape
• write-preflight existing-file behavior
• Deep Review shared-context post-call measurement path

Validation

• rustfmt --edition 2024 --check --config skip_children=true src\crates\core\src\agentic\tools\tool_context_runtime.rs src\crates\core\src\agentic\execution\execution_engine.rs src\crates\core\src\agentic\execution\round_executor.rs src\crates\core\src\agentic\tools\framework.rs src\crates\core\src\agentic\tools\pipeline\tool_pipeline.rs src\crates\core\src\agentic\tools\mod.rs
• node scripts\check-core-boundaries.mjs
• $env:BITFUN_BOUNDARY_CHECK_SELF_TEST='1'; node scripts\check-core-boundaries.mjs
• git diff --check gcwing/main..HEAD
• cargo test -p bitfun-core tool_context_runtime -- --nocapture
• cargo test -p bitfun-core pipeline_preserves_core_owned_tool_context_without_portable_runtime_leak -- --nocapture
• cargo test -p bitfun-core shared_context_tests -- --nocapture
• cargo test -p bitfun-core write_preflight -- --nocapture
• cargo check -p bitfun-core --features product-full
• cargo check -p bitfun-core --no-default-features