fix(eager): don't defer meta-context variables during deferred import

[jasmith-hs]

Description

During eager execution, importing a template that depends on deferred values routes through
ImportTag.handleDeferredNodesDuringImport. Its flat/no-alias branch wrapped every child
binding in a DeferredValue before propagating it to the parent context.

The problem is that this swept up meta-context variables too — most importantly
import_resource_path. Its concrete String value was replaced with a value-less
DeferredValue, so a later EagerMacroFunction.reconstructImage() read a DeferredValue where it
expected a String, losing the import path (and risking a ClassCastException) when reconstructing
an imported macro.

Meta-context variables are already classified via
MetaContextVariables.isMetaContextVariable(...) and excluded from dependency tracking,
speculative binding reconstruction, and deferred-token processing everywhere else in eager
execution. This one code path bypassed that classification.

What changed

• ImportTag.handleDeferredNodesDuringImport now skips meta-context variables in the flat
  branch rather than deferring them. This mirrors the non-deferred integrateChild path
  (getChildBindingsWithoutImportResourcePath), which already excludes import_resource_path from
  parent propagation — the value stays alive only in the macro's captured localContextScope.
• EagerMacroFunction.reconstructImage defensively unwraps a DeferredValue before the String
  cast, so a stray wrapper can never throw.

This description was authored by Claude Code.

BRAVE

Backwards Compatibility

• Behavior change is confined to eager-execution deferred-import handling.
• Brings the deferred flat-import path in line with the already-correct non-deferred path.

Rollout and Rollback Plan

• Standard library release; no data migration or config.
• Rollback is a straight revert of this commit.

Automated Testing

• New EagerImportTagTest.itDoesNotDeferMetaContextVariablesDuringDeferredImport proves meta-context
  variables are not deferred into the parent while normal bindings still defer with originalValue
  preserved.
• Full eager/import/macro suites pass (EagerTest, EagerImportTagTest, EagerFromTagTest,
  ImportTagTest, MacroTagTest, EagerMacroFunctionTest): 300 tests, 0 failures.

Verification

• A/B tested "skip" vs the initial "put as-is": every end-to-end reconstruction test passes with
  "skip", confirming nothing relies on the parent receiving the meta value.

Expect Dependencies to Fail

• None expected; eager execution is Beta and this only tightens deferred-import handling.

REVIEWERS: Please review both the code changes and the answers above, and validate that they match the expectations for BRAVE