fix: avoid panic when range starts past object end

[shikhar]

Summary

• guard page slicing when range starts beyond object end
• return RangeNotSatisfied instead of panicking
• add unit test covering out-of-bounds start within last page

Testing

• cargo +nightly fmt
• cargo clippy --all-features --all-targets -- -D warnings --allow deprecated
• cargo nextest run

Closes #54

[greptile-apps]

Greptile Overview

Greptile Summary

Refactored page slicing logic to properly handle out-of-bounds range requests instead of panicking.

• Extracted inline slicing code into dedicated slice_page_data function
• Added bounds check: returns RangeNotSatisfied error when range start exceeds page data length
• Changed stream combinator from map_ok to and_then to propagate errors
• Added unit test slice_page_data_rejects_range_start_past_object_end covering the edge case

The fix follows Rust best practices from CLAUDE.md by using explicit error handling with Result<T, E> instead of allowing panics on out-of-bounds slice operations.

Confidence Score: 5/5

• Safe to merge - critical bug fix with proper error handling and test coverage
• Addresses a panic scenario with idiomatic Rust error handling, includes comprehensive unit test, follows project style guide, and maintains existing behavior for valid ranges
• No files require special attention

Important Files Changed

Filename	Overview
src/service/mod.rs	extracted panic-prone slicing logic into slice_page_data with bounds checking, added test coverage

Sequence Diagram

sequenceDiagram
    participant Client
    participant CacheyService
    participant Stream
    participant slice_page_data
    participant Cache

    Client->>CacheyService: get(range)
    CacheyService->>Stream: iter pages in range
    loop for each page
        Stream->>Cache: fetch page
        Cache-->>Stream: (page_id, value)
        Stream->>slice_page_data: validate & slice(page_id, range, value)
        alt start_offset >= data_len
            slice_page_data-->>Stream: RangeNotSatisfied error
            Stream-->>Client: 416 Range Not Satisfiable
        else valid range
            slice_page_data-->>Stream: (sliced_data, range)
            Stream-->>Client: Chunk
        end
    end

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