docs: fix nested agent guide loading and trim root AGENTS.md

[Xuanwo]

rust/AGENTS.md and docs/src/format/AGENTS.md were never reaching coding agents. Nested guides are discovered through a CLAUDE.md entry point in the directory — protos/, python/, and java/ each have one, but those two directories did not. The Rust guide is the largest and most safety-relevant of the set, carrying the spawn_cpu() non-blocking contract, the RowAddr/RowId type separation, and the lance-encoding hot-path rules, so agents editing rust/ had none of it in context.

The root AGENTS.md also carried a hand-maintained crate list that duplicates what ls rust/ and each crate's Cargo.toml description already state, and it had drifted: arrow-scalar, arrow-stats, lance-derive, lance-index-core, lance-namespace-datafusion, lance-select, and lance-tokenizer were all missing. A stale map is worse than no map, and every session that loads the file pays for it. The directory-guide pointer above the list is unchanged, so navigation is unaffected.

The format vote reminder will fire on this PR because it adds a path under docs/src/format/. That path is a symlink to the agent guide already in that directory; the format specification itself is untouched.

[github-actions]

Important

This PR touches the Lance format specification.

Substantive changes to the format specification — the .proto definitions
and the spec docs under docs/src/format/ — require a PMC vote before merge.
Minor edits such as typo fixes, wording, or formatting are excluded; use your
judgment.

If this is a meaningful format change:

• Start a vote following the Lance community voting process.
  Format specification modifications need 3 binding +1 votes (excluding the
  proposer), held on GitHub Discussions, with a minimum voting period of 1 week.
• Once the vote passes, link the completed vote in this PR. It should not be
  merged until the vote is linked.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

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Run ID: 8ccaaa69-b5fb-418a-857b-13a1946eae68

📥 Commits

Reviewing files that changed from the base of the PR and between 9225744 and 5f72270.

📒 Files selected for processing (3)

• AGENTS.md
• docs/src/format/CLAUDE.md
• rust/CLAUDE.md

💤 Files with no reviewable changes (1)

• AGENTS.md

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📝 Walkthrough

Walkthrough

The Architecture section was removed from AGENTS.md. The format and Rust CLAUDE.md files now symbolically link to AGENTS.md.

Changes

Guidance consolidation

Layer / File(s)	Summary
Update root guidance AGENTS.md	Removes the Rust workspace Architecture section.
Link subordinate guidance docs/src/format/CLAUDE.md, rust/CLAUDE.md	Replaces independent guidance content with symbolic links to AGENTS.md.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• lance-format/lance#7779: Updates related AGENTS.md guidance and the linked CLAUDE.md files.

Suggested labels: documentation, A-format

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main changes: adding agent guide entry points and removing the outdated root AGENTS.md list.
Description check	✅ Passed	The description is clearly related to the PR and explains the nested guide entry points and root AGENTS.md cleanup.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch xuanwo/agents-md-nested-guide-loading

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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