trace: add execution route visibility + debug passthrough; phase2170 canaries; docs

- Add HAKO_TRACE_EXECUTION to trace executor route
  - Rust hv1_inline: stderr [trace] executor: hv1_inline (rust)
  - Hakovm dispatcher: stdout [trace] executor: hakovm (hako)
  - test_runner: trace lines for hv1_inline/core/hakovm routes
- Add HAKO_VERIFY_SHOW_LOGS and HAKO_DEBUG=1 (enables both)
  - verify_v1_inline_file() log passthrough with numeric rc extraction
  - test_runner exports via HAKO_DEBUG
- Canary expansion under phase2170 (state spec)
  - Array: push×5/10 → size, len/length alias, per‑recv/global, flow across blocks
  - Map: set dup-key non-increment, value_state get/has
  - run_all.sh: unify, remove SKIPs; all PASS
- Docs
  - ENV_VARS.md: add Debug/Tracing toggles and examples
  - PLAN.md/CURRENT_TASK.md: mark 21.7 green, add Quickstart lines

All changes gated by env vars; default behavior unchanged.

src/runtime/provider_lock.rs

@@ -7,7 +7,7 @@
 
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, OnceLock};
-use crate::boxes::file::provider::FileIo;
+use crate::boxes::file::provider::{FileCaps, FileIo};
 
 static LOCKED: AtomicBool = AtomicBool::new(false);
 static WARN_ONCE: OnceLock<()> = OnceLock::new();
@@ -49,3 +49,8 @@ pub fn get_filebox_provider() -> Option<&'static Arc<dyn FileIo>> {
     FILEBOX_PROVIDER.get()
 }
 
+/// Convenience: fetch current FileBox provider capabilities (if initialized).
+/// Returns None when no provider is registered yet.
+pub fn get_filebox_caps() -> Option<FileCaps> {
+    get_filebox_provider().map(|p| p.caps())
+}