fix: resolve critical deadlocks and infinite loops

[renich]

Description

This PR addresses several fundamental stability issues that caused the Crystalline server to hang indefinitely or become unresponsive to SIGINT (Ctrl+C). These fixes are critical for the reliability of the server, especially in single-threaded environments or when used with diverse LSP clients.

Key Changes

1. Infinite Loop in Workspace Completion

• Problem: In Workspace#completion, the lexer loop was comparing token.type (an Enum) to a symbol (:EOF). This comparison always returned false, causing the server to spin indefinitely when lexing comments.
• Fix: Updated the comparison to use the idiomatic Crystal enum predicate methods (.eof? and .comment?).

2. Deadlock in Single-Threaded Mode (-Dpreview_mt absent)

• Problem: Analysis.spawn_dedicated enqueued a fiber on the current thread and then immediately blocked the main fiber on a channel. In single-threaded mode, the scheduler never had a chance to switch to the compilation fiber, leading to a permanent deadlock.
• Fix: Refactored spawn_dedicated to execute the compilation block immediately (synchronously) when multithreading is disabled, ensuring the channel is populated before the main fiber waits.

3. Progress Report Hang

• Problem: Progress#report assumed all clients would respond to a workDoneProgress/create request. If a client (or a test mock) didn't support progress or didn't send a response, the server would hang waiting for an on_response callback.
• Fix: Added a capability check for work_done_progress. If unsupported, the report executes the block immediately rather than waiting for a client handshake.

4. Buffered Sync Channel

• Problem: The compilation synchronization channel was unbuffered, which could lead to blocking during synchronous execution paths.
• Fix: Introduced a buffer of 1 to the sync_channel to ensure non-blocking completion of the compilation block.

Verification

• New Spec: Added spec/reproduction_76_spec.cr which empirically reproduces the comment-completion hang and verifies the fix.
• Cross-Platform: Verified that the test suite passes with 100% success in both Single-Threaded and Multi-Threaded (-Dpreview_mt) modes.
• Responsiveness: Confirmed that the server now correctly handles SIGINT even during heavy compilation tasks.

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Maintainer Note

These stability fixes are prerequisites for running the full test suite reliably. Without them, specific edge cases in comment lexing or single-threaded execution can cause the test runner itself to hang.

Assisted-by: Gemini gemini@google.com

[renich]

This PR addresses and fixes issues #76 and #20. (Foundational stability fixes for hangs and infinite loops).