fix(runtime): keep inherited history parent-owned

[codeforester]

Summary

• Keep completion history ownership with the invocation that created the run bundle.
• Prevent inherited Base children from marking the parent bundle complete.
• Clarify the delegated-history contract and add regression coverage.

Issue

Fixes #2083

Follow-up to #2080.

Validation

• bats --print-output-on-failure cli/bash/commands/basectl/tests/runtime-dispatch.bats — 40 passed
• bats --print-output-on-failure cli/bash/commands/basectl/tests/workspace.bats — 15 passed
• Workspace clone tests — 5 passed
• Real workspace dry-run fan-out — 0 inherited-context warnings, 1 primary history row, 1 run bundle
• ./bin/base-test — 1,115 Python and 899 BATS passed
• ShellCheck and git diff --check passed

Docs Impact

Updated docs/observability.md to document that inherited Base children do not write separate completion records or mutate the parent lifecycle.

Workspace clone semantics and repository materialization behavior are unchanged.