feat: add a helper for the most recent entries

[HadesArchitect]

Several places want to show only the tail of a list — the last few keyspaces touched, the last few ids in a debug line. Pull that out so it is written once.

Call sites follow in the next PR.

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Summary by CodeRabbit

• Bug Fixes
  • Improved handling of recent item lists by safely limiting results to the requested number while preserving their order.

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Walkthrough

The Cassandra session package adds a private lastN helper for returning up to the last n string-slice entries.

Changes

Cassandra session utility

Layer / File(s)	Summary
Add lastN slice helper pkg/cassandra/session.go	Adds handling for non-positive limits, short slices, and suffix extraction while preserving entry order.

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

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Title check	✅ Passed	The title clearly describes the addition of a helper for retrieving the most recent entries.

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@pkg/cassandra/session.go`:
- Line 195: Resolve the unused private helper lastN before merging: either add
an appropriate caller in the same package or add a same-package test that
exercises it; if neither is needed, remove or defer lastN until a caller is
ready so the unused lint check passes.
- Line 203: Update the suffix slice expression in the surrounding session method
to start at len(s)-n rather than len(s)-n-1, ensuring it returns exactly n
entries when the slice contains more than n elements.

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• pkg/cassandra/session.go

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pkg/**

⚙️ CodeRabbit configuration file

Go backend using the Grafana backend plugin SDK and the gocql driver. Check for Cassandra query safety, connection/session lifecycle, and TLS handling.

Files:

• pkg/cassandra/session.go

🪛 golangci-lint (2.12.2)

pkg/cassandra/session.go

[error] 195-195: func lastN is unused

(unused)

[coderabbitai]

🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

Fix the suffix start index.

Use len(s)-n, not len(s)-n-1. The current code returns n+1 entries when the slice is longer than n.

Proposed fix

-	return s[len(s)-n-1:]
+	return s[len(s)-n:]

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	return s[len(s)-n-1:]
	return s[len(s)-n:]

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@pkg/cassandra/session.go` at line 203, Update the suffix slice expression in
the surrounding session method to start at len(s)-n rather than len(s)-n-1,
ensuring it returns exactly n entries when the slice contains more than n
elements.