fix: revert to per-resource watcher + increase FD limit at startup

[johnlanni]

Problem

PR #236's shared watcher approach causes runtime failure:

command failed err="failed to create shared file watcher: too many open files"

Root Cause Analysis

The shared watcher design has fundamental architectural flaws:

1. Event channel conflict: Each fileREST instance starts a goroutine reading from the same watcher.Events channel

   • Multiple goroutines competing for events
   • Events are distributed randomly (only one goroutine receives each event)
   • Resources miss their own file change events

2. Directory watch conflicts: Each resource calls dirWatcher.Add(objRootPath) on different subdirectories

   • Potentially causes fsnotify internal issues

3. Still hits FD limit: Even with shared watcher, other initialization steps may consume FDs before watcher creation

Solution

Revert to per-resource watcher (simpler & correct) + increase system FD limit early:

Changes

1. main.go: Add init() to increase FD limit to 65535 before any initialization

   • Runs before any watcher/file operations
   • Logs current and updated limits for debugging
   • Gracefully handles permission errors

2. file_rest.go: Restore per-resource watcher creation

   • Each resource gets isolated event stream (correct behavior)
   • Add resource name to error messages for debugging
   • Properly close watcher in Destroy()

3. apiserver.go: Remove shared watcher logic

   • Simplify code
   • Remove fsnotify import

Why This Works

• FD limit increased early: Before any file operations
• Proper event isolation: Each resource processes only its own events
• Simpler architecture: Less complexity = fewer bugs
• Typical deployments have <50 resources: Even at 1 watcher/resource, well under 65535 limit

Testing

• Compiles successfully
• FD limit increased at startup (logged)
• Each resource independently watches its directory
• No event distribution conflicts

Alternative Considered

A truly shared watcher would require:

• Single goroutine reading events
• Event dispatcher routing to correct resource based on file path
• Complex synchronization

This adds significant complexity for minimal benefit given FD limits are easily increased.

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Supersedes #236 and #237

[lingma-agents]

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🔄 分支流向: fix/centralized-watcher-dispatcher ➜ main

📦 提交: 审查当前PR从a67f011到87d6aae的提交。

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📒 文件清单 （3 个文件）

📝 变更: 3 个文件

📝 变更文件:

• src/apiserver/main.go
• src/apiserver/pkg/apiserver/apiserver.go
• src/apiserver/pkg/registry/file_rest.go

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