feat: add short-index support for 'xhs read'

[Pleasurecruise]

Introduce short-index navigation so users can open listed notes with xhs read <N>. Persist an ordered index from listing commands (search/feed/hot/user-posts) and resolve numeric indices in the read command to note_id + xsec_token. Key changes:

• Add INDEX_CACHE_FILE constant and .idea to .gitignore.
• Implement save_note_index() and get_note_by_index() in xhs_cli/cookies.py (reads/writes index cache, enforces 0o600 perms).
• Add _save_index_from_items() and wire it into search, feed, hot, and user-posts in xhs_cli/commands/reading.py; allow read to accept numeric indices and raise a usage error when missing.
• Add comprehensive tests for CLI index behavior and cookies index handling (tests/test_cli.py, tests/test_cookies.py).

This change improves interactive ergonomics by avoiding manual copying of long note IDs when opening results from recent listings.

[Copilot]

Pull request overview

Adds “short-index” navigation so users can open recently listed notes via xhs read <N> by persisting the last listing’s ordered note index to disk and resolving numeric args in read.

Changes:

• Persist a ~/.xiaohongshu-cli/index_cache.json note index from listing commands and enforce 0600 permissions.
• Extend xhs read to accept numeric indices and resolve them to {note_id, xsec_token}.
• Add unit tests covering index persistence and CLI index resolution; update docs to describe the workflow.

Reviewed changes

Copilot reviewed 7 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
xhs_cli/cookies.py	Adds index cache path + save/load helpers for short-index lookups.
xhs_cli/constants.py	Introduces INDEX_CACHE_FILE constant.
xhs_cli/commands/reading.py	Saves index during listing commands and resolves numeric read arguments.
tests/test_cookies.py	Adds tests for index cache persistence, permissions, and lookup behavior.
tests/test_cli.py	Adds CLI tests for reading by short index and index extraction from results.
README.md	Documents short-index navigation usage and cache location.
SKILL.md	Updates command docs/examples to include short-index read workflow.
.gitignore	Ignores .idea.
uv.lock	Bumps project version and updates locked dependencies.

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[jackwener]

Thanks for the idea and the original implementation here — the short-index workflow is genuinely useful, and I pulled that idea forward into a replacement PR: #17.

I am closing this PR in favor of #17 because that branch is rebased on current main and keeps the newer note-context hardening intact:

• it preserves xsec_source alongside xsec_token for short-index reads/comments
• it clears the index cache on empty list results, so old indices are not reused accidentally
• it applies cleanly on top of the current codebase without the conflicts in this branch

I also added a Co-authored-by trailer so the implementation still credits your contribution. Please take a look at #17.