fix: remove dead delete+recreate and pin code, add poll fallback test

Phase 1 cleanup:
- Remove deletePost() method (dead code, replaced by PUT in-place updates)
- Remove _postInfo Map tracking (no longer needed)
- Remove pin/unpin API calls from watcher-manager.js (incompatible with PUT updates)
- Add JSDoc note on (edited) label limitation in _flushUpdate()
- Add integration test: test/integration/poll-fallback.test.js
- Fix addSession() lastOffset===0 falsy bug (0 was treated as 'no offset')
- Fix pre-existing test failures: add lastOffset:0 where tests expect backlog reads
- Fix pre-existing session-monitor test: create stub transcript files
- Fix pre-existing status-formatter test: update indent check for blockquote format
- Format plugin/ files with Prettier (pre-existing formatting drift)

plugin/server/configuration.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"fmt"
+)
+
+// Configuration holds the plugin settings from the Admin Console.
+type Configuration struct {
+	SharedSecret      string `json:"SharedSecret"`
+	MaxActiveSessions int    `json:"MaxActiveSessions"`
+	MaxStatusLines    int    `json:"MaxStatusLines"`
+}
+
+// Clone returns a shallow copy of the configuration.
+func (c *Configuration) Clone() *Configuration {
+	var clone Configuration
+	clone = *c
+	return &clone
+}
+
+// IsValid checks if the configuration is valid.
+func (c *Configuration) IsValid() error {
+	if c.SharedSecret == "" {
+		return fmt.Errorf("SharedSecret must not be empty")
+	}
+	if c.MaxActiveSessions <= 0 {
+		c.MaxActiveSessions = 20
+	}
+	if c.MaxStatusLines <= 0 {
+		c.MaxStatusLines = 30
+	}
+	return nil
+}
+
+// getConfiguration retrieves the active configuration under lock.
+func (p *Plugin) getConfiguration() *Configuration {
+	p.configurationLock.RLock()
+	defer p.configurationLock.RUnlock()
+
+	if p.configuration == nil {
+		return &Configuration{
+			MaxActiveSessions: 20,
+			MaxStatusLines:    30,
+		}
+	}
+
+	return p.configuration
+}
+
+// OnConfigurationChange is invoked when configuration changes may have been made.
+func (p *Plugin) OnConfigurationChange() error {
+	var configuration = new(Configuration)
+
+	if err := p.API.LoadPluginConfiguration(configuration); err != nil {
+		return fmt.Errorf("failed to load plugin configuration: %w", err)
+	}
+
+	// Apply defaults
+	if configuration.MaxActiveSessions <= 0 {
+		configuration.MaxActiveSessions = 20
+	}
+	if configuration.MaxStatusLines <= 0 {
+		configuration.MaxStatusLines = 30
+	}
+
+	p.configurationLock.Lock()
+	p.configuration = configuration
+	p.configurationLock.Unlock()
+
+	return nil
+}