Reset Hot Reload _disabled flag when a new debug session starts

[noiseonwires]

ManagedHotReloadLanguageServiceImpl._disabled is set to true whenever an unexpected exception is caught StartSessionAsync, BreakStateOrCapabilitiesChangedAsync, EndSessionAsync. Once set, the flag is never cleared - EndSessionAsync does not reset it and StartSessionAsync early-returns when it is true. This means a single failure permanently disables Hot Reload for the lifetime of the Roslyn process, even across debug session restarts. Users have to restart Visual Studio / the Roslyn LSP server to recover.

As discussed with @tmat some time ago, this change clears _disabled at the start of StartSessionAsync so that a fresh debug session is always given a chance to initialize. Any exception that flipped the flag is still a product bug worth fixing on its own, but this avoids a confusing and unrecoverable user-facing state where Hot Reload silently does nothing for the rest of the IDE session.

Investigated as part of a report where Hot Reload worked exactly once per Roslyn process and then stopped responding until the process was restarted.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Resets the Managed Hot Reload service’s _disabled flag on each new debug session so prior session failures don’t permanently disable Hot Reload.

Changes:

• Removed the early-return when _disabled is set at session start.
• Added logic to always reset _disabled to false at the beginning of StartSessionAsync, with explanatory comments.