refactor: major codebase cleanup - BDD comments, file splitting, bug fixes (#1350)

* style(tests): normalize BDD comments from '// #given' to '// given'

- Replace 4,668 Python-style BDD comments across 107 test files
- Patterns changed: // #given -> // given, // #when -> // when, // #then -> // then
- Also handles no-space variants: //#given -> // given

* fix(rules-injector): prefer output.metadata.filePath over output.title

- Extract file path resolution to dedicated output-path.ts module
- Prefer metadata.filePath which contains actual file path
- Fall back to output.title only when metadata unavailable
- Fixes issue where rules weren't injected when tool output title was a label

* feat(slashcommand): add optional user_message parameter

- Add user_message optional parameter for command arguments
- Model can now call: command='publish' user_message='patch'
- Improves error messages with clearer format guidance
- Helps LLMs understand correct parameter usage

* feat(hooks): restore compaction-context-injector hook

- Restore hook deleted in cbbc7bd0 for session compaction context
- Injects 7 mandatory sections: User Requests, Final Goal, Work Completed,
  Remaining Tasks, Active Working Context, MUST NOT Do, Agent Verification State
- Re-register in hooks/index.ts and main plugin entry

* refactor(background-agent): split manager.ts into focused modules

- Extract constants.ts for TTL values and internal types (52 lines)
- Extract state.ts for TaskStateManager class (204 lines)
- Extract spawner.ts for task creation logic (244 lines)
- Extract result-handler.ts for completion handling (265 lines)
- Reduce manager.ts from 1377 to 755 lines (45% reduction)
- Maintain backward compatible exports

* refactor(agents): split prometheus-prompt.ts into subdirectory

- Move 1196-line prometheus-prompt.ts to prometheus/ subdirectory
- Organize prompt sections into separate files for maintainability
- Update agents/index.ts exports

* refactor(delegate-task): split tools.ts into focused modules

- Extract categories.ts for category definitions and routing
- Extract executor.ts for task execution logic
- Extract helpers.ts for utility functions
- Extract prompt-builder.ts for prompt construction
- Reduce tools.ts complexity with cleaner separation of concerns

* refactor(builtin-skills): split skills.ts into individual skill files

- Move each skill to dedicated file in skills/ subdirectory
- Create barrel export for backward compatibility
- Improve maintainability with focused skill modules

* chore: update import paths and lockfile

- Update prometheus import path after refactor
- Update bun.lock

* fix(tests): complete BDD comment normalization

- Fix remaining #when/#then patterns missed by initial sed
- Affected: state.test.ts, events.test.ts

---------

Co-authored-by: justsisyphus <justsisyphus@users.noreply.github.com>

src/tools/delegate-task/helpers.ts

@@ -0,0 +1,100 @@
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
+import { MESSAGE_STORAGE } from "../../features/hook-message-injector"
+import type { DelegateTaskArgs } from "./types"
+
+/**
+ * Parse a model string in "provider/model" format.
+ */
+export function parseModelString(model: string): { providerID: string; modelID: string } | undefined {
+  const parts = model.split("/")
+  if (parts.length >= 2) {
+    return { providerID: parts[0], modelID: parts.slice(1).join("/") }
+  }
+  return undefined
+}
+
+/**
+ * Get the message directory for a session, checking both direct and nested paths.
+ */
+export function getMessageDir(sessionID: string): string | null {
+  if (!existsSync(MESSAGE_STORAGE)) return null
+
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) return directPath
+
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) return sessionPath
+  }
+
+  return null
+}
+
+/**
+ * Format a duration between two dates as a human-readable string.
+ */
+export function formatDuration(start: Date, end?: Date): string {
+  const duration = (end ?? new Date()).getTime() - start.getTime()
+  const seconds = Math.floor(duration / 1000)
+  const minutes = Math.floor(seconds / 60)
+  const hours = Math.floor(minutes / 60)
+
+  if (hours > 0) return `${hours}h ${minutes % 60}m ${seconds % 60}s`
+  if (minutes > 0) return `${minutes}m ${seconds % 60}s`
+  return `${seconds}s`
+}
+
+/**
+ * Context for error formatting.
+ */
+export interface ErrorContext {
+  operation: string
+  args?: DelegateTaskArgs
+  sessionID?: string
+  agent?: string
+  category?: string
+}
+
+/**
+ * Format an error with detailed context for debugging.
+ */
+export function formatDetailedError(error: unknown, ctx: ErrorContext): string {
+  const message = error instanceof Error ? error.message : String(error)
+  const stack = error instanceof Error ? error.stack : undefined
+
+  const lines: string[] = [
+    `${ctx.operation} failed`,
+    "",
+    `**Error**: ${message}`,
+  ]
+
+  if (ctx.sessionID) {
+    lines.push(`**Session ID**: ${ctx.sessionID}`)
+  }
+
+  if (ctx.agent) {
+    lines.push(`**Agent**: ${ctx.agent}${ctx.category ? ` (category: ${ctx.category})` : ""}`)
+  }
+
+  if (ctx.args) {
+    lines.push("", "**Arguments**:")
+    lines.push(`- description: "${ctx.args.description}"`)
+    lines.push(`- category: ${ctx.args.category ?? "(none)"}`)
+    lines.push(`- subagent_type: ${ctx.args.subagent_type ?? "(none)"}`)
+    lines.push(`- run_in_background: ${ctx.args.run_in_background}`)
+    lines.push(`- load_skills: [${ctx.args.load_skills?.join(", ") ?? ""}]`)
+    if (ctx.args.session_id) {
+      lines.push(`- session_id: ${ctx.args.session_id}`)
+    }
+  }
+
+  if (stack) {
+    lines.push("", "**Stack Trace**:")
+    lines.push("```")
+    lines.push(stack.split("\n").slice(0, 10).join("\n"))
+    lines.push("```")
+  }
+
+  return lines.join("\n")
+}