refactor: simplify error wrapping and progress reporting

- Extract getErrorMessage() and createInstallError() to eliminate
copy-paste error wrapping in fetchQueue, linkQueue, and pipeline
- Flatten nested conditionals in bus.ts emitFetched with early return
- Fix double computation of formatProgressLine in complete()
- Fix implicit fall-through in render() with guard clause
- Wrap JSON.parse in isSkillUpToDate with its own try/catch

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: SoonIter

packages/skills-package-manager/src/pipeline/fetchQueue.ts

@@ -1,6 +1,6 @@
 import { access, lstat, readFile, readlink } from 'node:fs/promises'
 import path from 'node:path'
-import { ErrorCode, SpmError } from '../errors'
+import { createInstallError } from '../errors'
 import { fetchSkill } from '../fetchers'
 import { applySkillPatch } from '../patches/skillPatch'
 import { createTaskQueue, type TaskQueue } from './queue'
@@ -17,9 +17,6 @@ async function isSkillUpToDate(
   const skillDir = path.join(rootDir, installDir, skillName)
 
   try {
-    // Verify SKILL.md exists — a stale marker alone is not sufficient
-    await access(path.join(skillDir, 'SKILL.md'))
-
     const stats = await lstat(skillDir)
 
     if (entry.resolution.type === 'link') {
@@ -30,8 +27,16 @@ async function isSkillUpToDate(
       return resolvedTarget === expectedTarget
     }
 
+    // A marker alone is not sufficient — verify the skill content is present
+    await access(path.join(skillDir, 'SKILL.md'))
+
     const markerPath = path.join(skillDir, '.skills-pm.json')
-    const marker = JSON.parse(await readFile(markerPath, 'utf8'))
+    let marker: { installedBy?: string; digest?: string } | undefined
+    try {
+      marker = JSON.parse(await readFile(markerPath, 'utf8'))
+    } catch {
+      return false
+    }
     return marker?.installedBy === 'skills-package-manager' && marker?.digest === entry.digest
   } catch {
     return false
@@ -79,12 +84,7 @@ export function createFetchTaskQueue(
       bus.emitFetched(result)
       return result
     } catch (error) {
-      throw new SpmError({
-        code: ErrorCode.INSTALL_ERROR,
-        message: `Failed to fetch skill "${task.skillName}": ${error instanceof Error ? error.message : String(error)}`,
-        cause: error instanceof Error ? error : undefined,
-        context: { skillName: task.skillName, phase: 'fetch' },
-      })
+      throw createInstallError('fetch', task.skillName, error)
     }
   }
 

packages/skills-package-manager/src/pipeline/index.ts

@@ -1,7 +1,7 @@
 import { access } from 'node:fs/promises'
 import path from 'node:path'
 import type { SkillsLock, SkillsLockEntry } from '../config/types'
-import { ErrorCode, SpmError } from '../errors'
+import { ErrorCode, getErrorMessage, SpmError } from '../errors'
 import { writeInstallState } from '../install/installState'
 import { pruneManagedSkills } from '../install/pruneManagedSkills'
 import { installStageHooks } from '../install/withBundledSelfSkillLock'
@@ -155,7 +155,7 @@ export async function runPipeline(input: RunPipelineInput): Promise<PipelineResu
       code: ErrorCode.INSTALL_ERROR,
       message: `${errors.length} skills failed to install`,
       cause: first instanceof Error ? first : undefined,
-      context: { errors: errors.map((e) => (e instanceof Error ? e.message : String(e))) },
+      context: { errors: errors.map(getErrorMessage) },
     })
   }
 

packages/skills-package-manager/src/pipeline/linkQueue.ts

@@ -1,4 +1,4 @@
-import { ErrorCode, SpmError } from '../errors'
+import { createInstallError } from '../errors'
 import { linkSkill } from '../install/links'
 import { createTaskQueue, type TaskQueue } from './queue'
 import type { LinkResult, LinkTask, PipelineBus, WorkspaceContext } from './types'
@@ -23,12 +23,7 @@ export function createLinkTaskQueue(
       bus.emitLinked(result)
       return result
     } catch (error) {
-      throw new SpmError({
-        code: ErrorCode.INSTALL_ERROR,
-        message: `Failed to link skill "${task.skillName}": ${error instanceof Error ? error.message : String(error)}`,
-        cause: error instanceof Error ? error : undefined,
-        context: { skillName: task.skillName, phase: 'link' },
-      })
+      throw createInstallError('link', task.skillName, error)
     }
   }