fix(Bot): Recover stalled taxi flights - #2865

Pull Request Description

Fixes random bots becoming permanently stuck in taxi state when their flight movement spline stops progressing.

Taxi recovery is moved into PlayerbotAI, where it runs consistently for every bot currently marked as in flight instead of depending on the New RPG travel action being selected.

The watchdog:

• Tracks changes in map, taxi route node, spline index, and physical position.
• Continues valid taxi routes across map boundaries.
• Attempts one controlled restart when a same-map flight spline stalls.
• After 15 seconds without progress, safely cleans up the taxi state.
• Teleports the bot to the route’s validated final taxi node when recovery cannot resume.
• Leaves normal maintenance and stuck recovery to handle the bot when no valid final destination is available.

Healthy taxi flights retain their existing behavior.

Closes #2863

Feature Evaluation

• Describe the minimum logic required to achieve the intended behavior.

  A small per-bot watchdog records the most recent taxi progress indicators. Recovery is attempted only when the bot is currently in flight and the spline has stopped progressing. It first attempts to resume the existing route, then uses a bounded cleanup fallback.

• Describe the processing cost when this logic executes across many bots.

  All bots perform a cheap IsInFlight() check during their normal AI update. Bots that are not flying immediately bypass the remaining logic. Flying bots perform a small number of integer comparisons and a squared-distance calculation. There are no database queries, path searches, or unbounded loops. Recovery and destination lookups occur only while handling a taxi flight.

How to Test the Changes

1. Build and start the server with random Playerbots enabled.
2. Allow bots to use normal taxi routes, including routes that cross map boundaries.
3. Confirm healthy taxi flights continue and finish normally.
4. Observe a bot whose flight spline becomes finalized or stops moving while it remains in taxi state.
5. Confirm the watchdog attempts one route or spline recovery.
6. If the flight still makes no progress for 15 seconds, confirm that:
   • The flight movement generator is removed.
   • Taxi state and flags are cleared.
   • The bot is placed at the validated final taxi node when one is available.
   • The bot resumes normal AI behavior instead of remaining permanently stuck.
7. Review the playerbots log messages for cross-map continuation, restart attempts, and fallback cleanup.

The change was exercised on a live local realm during two approximately 24-hour soak test. Follow-up checks did not find bots remaining indefinitely stuck in taxi state.

Impact Assessment

• Does this change increase per-bot/per-tick processing or risk scaling poorly with thousands of bots?

  • • No, not at all
  • • Minimal impact (explain below)
  • • Moderate impact (explain below)

  The normal per-bot cost is an IsInFlight() check. Additional progress comparisons run only for bots actively using a taxi. The watchdog has a fixed amount of state and all recovery attempts are bounded.

• Does this change modify default bot behavior?

  • • No
  • • Yes (explain why)

  It changes failure handling for bots whose taxi movement stops progressing. Normal, progressing taxi flights are not intentionally changed.

• Does this change add new decision branches or increase maintenance complexity?

  • • No
  • • Yes (explain below)

  It adds a contained taxi-recovery state machine to PlayerbotAI. The additional branches distinguish healthy progress, cross-map continuation, one restart attempt, and final cleanup. Recovery is bounded to keep its behavior predictable.

AI Assistance

Was AI assistance used while working on this change?

• • No
• • Yes (explain below)

I used GPT-5.6 Sol High to assist in investigating the flight failures and architecting a solution for flight recovery. I also utilized it's assistance in implementation, monitoring bot health after the changes over two 24 hour peroids, and making sure I had everything lined up to try to contribute back in the least headache inducing way possible for the team.

Code Provenance / Attribution

Was any code in this PR copied or adapted from a sister / upstream project (e.g. CMaNGOS playerbots, MaNGOS, another module)?

• • No, all code in this PR is original
• • Yes (name the project and the original author(s) below)

Final Checklist

• • Changes are understood and tested for server stability and performance impact.
• • Any new bot dialogue lines are translated. (No dialogue was added.)
• • New source files use the GPLv2 header. (No new source files were added.)
• • Documentation updated if needed. (No configuration, commands, or user-facing behavior require documentation changes.)
• • New and modified files do not introduce new compiler warnings.

Notes for Reviewers

• Is PlayerbotAI::UpdateAI the appropriate centralized location for taxi recovery?
• Are the 15-second timeout and single restart attempt are suitable defaults?
• Does the final taxi-node validation and cleanup sequence cover all expected incomplete-route states?