[zhanghanduo]

Prepare the 0.18.2 patch release containing the trajectory fixes merged in #84 and #85.

Bump the project and lockfile version from 0.18.1 to 0.18.2, consolidate the two fix fragments into the dated changelog section, and remove the consumed fragments. Dependency pins are unchanged. Release notes describe authoritative history snapshots, ordered observer events, efficient nested-edit checks, conservative diagnostic lineage and unencodable-metadata fallback.

Validation:

• Full suite: 2403 passed, 1 skipped.
• Ruff, strict Pyright and unconsumed-field checks passed.
• Release validation and scripts/version.py --check-tag v0.18.2 passed; no pending fragments remain.
• Source distribution and wheel built successfully; both passed twine check.
• Built wheel installed and imported from site-packages in a clean Python 3.12.12 environment; installed distribution version is 0.18.2.
• Preflight confirmed GitHub/PyPI latest is 0.18.1 and 0.18.2 is not yet published.

After this PR is merged and main CI is green, create the annotated v0.18.2 tag on the merged main commit and push it. The release workflow revalidates the tagged tree, publishes to PyPI, then creates the GitHub Release with changelog notes and distribution assets.