feat(skills): add per-task skill spec auto-detection and injection

Replace external inject-spec.py hook with built-in zero-config skill
detection in codeagent-wrapper. The system auto-detects project type
from fingerprint files (go.mod, package.json, etc.), maps to installed
skills, and injects SKILL.md content directly into sub-agent prompts.

Key changes:
- Add DetectProjectSkills/ResolveSkillContent in executor/prompt.go
- Add Skills field to TaskSpec with parallel config parsing
- Add --skills CLI flag for explicit override
- Update /do SKILL.md Phase 4 with per-task skill examples
- Remove on-stop.py global hook (not needed)
- Replace inject-spec.py with no-op (detection now internal)
- Add 20 unit tests covering detection, resolution, budget, security

Security: path traversal protection via validSkillName regex,
16K char budget with tag overhead accounting, CRLF normalization.

Generated with SWE-Agent.ai

Co-Authored-By: SWE-Agent.ai <noreply@swe-agent.ai>

codeagent-wrapper/internal/app/cli.go

@@ -29,6 +29,7 @@ type cliOptions struct {
 	ReasoningEffort string
 	Agent           string
 	PromptFile      string
+	Skills          string
 	SkipPermissions bool
 	Worktree        bool
 
@@ -134,6 +135,7 @@ func addRootFlags(fs *pflag.FlagSet, opts *cliOptions) {
 	fs.StringVar(&opts.ReasoningEffort, "reasoning-effort", "", "Reasoning effort (backend-specific)")
 	fs.StringVar(&opts.Agent, "agent", "", "Agent preset name (from ~/.codeagent/models.json)")
 	fs.StringVar(&opts.PromptFile, "prompt-file", "", "Prompt file path")
+	fs.StringVar(&opts.Skills, "skills", "", "Comma-separated skill names for spec injection")
 
 	fs.BoolVar(&opts.SkipPermissions, "skip-permissions", false, "Skip permissions prompts (also via CODEAGENT_SKIP_PERMISSIONS)")
 	fs.BoolVar(&opts.SkipPermissions, "dangerously-skip-permissions", false, "Alias for --skip-permissions")
@@ -339,6 +341,16 @@ func buildSingleConfig(cmd *cobra.Command, args []string, rawArgv []string, opts
 		return nil, fmt.Errorf("task required")
 	}
 
+	var skills []string
+	if cmd.Flags().Changed("skills") {
+		for _, s := range strings.Split(opts.Skills, ",") {
+			s = strings.TrimSpace(s)
+			if s != "" {
+				skills = append(skills, s)
+			}
+		}
+	}
+
 	cfg := &Config{
 		WorkDir:            defaultWorkdir,
 		Backend:            backendName,
@@ -352,6 +364,7 @@ func buildSingleConfig(cmd *cobra.Command, args []string, rawArgv []string, opts
 		MaxParallelWorkers: config.ResolveMaxParallelWorkers(),
 		AllowedTools:       resolvedAllowedTools,
 		DisallowedTools:    resolvedDisallowedTools,
+		Skills:             skills,
 		Worktree:           opts.Worktree,
 	}
 
@@ -418,7 +431,7 @@ func runParallelMode(cmd *cobra.Command, args []string, opts *cliOptions, v *vip
 		return 1
 	}
 
-	if cmd.Flags().Changed("agent") || cmd.Flags().Changed("prompt-file") || cmd.Flags().Changed("reasoning-effort") {
+	if cmd.Flags().Changed("agent") || cmd.Flags().Changed("prompt-file") || cmd.Flags().Changed("reasoning-effort") || cmd.Flags().Changed("skills") {
 		fmt.Fprintln(os.Stderr, "ERROR: --parallel reads its task configuration from stdin; only --backend, --model, --full-output and --skip-permissions are allowed.")
 		return 1
 	}
@@ -585,6 +598,17 @@ func runSingleMode(cfg *Config, name string) int {
 		taskText = wrapTaskWithAgentPrompt(prompt, taskText)
 	}
 
+	// Resolve skills: explicit > auto-detect from workdir
+	skills := cfg.Skills
+	if len(skills) == 0 {
+		skills = detectProjectSkills(cfg.WorkDir)
+	}
+	if len(skills) > 0 {
+		if content := resolveSkillContent(skills, 0); content != "" {
+			taskText = taskText + "\n\n# Domain Best Practices\n\n" + content
+		}
+	}
+
 	useStdin := cfg.ExplicitStdin || shouldUseStdin(taskText, piped)
 
 	targetArg := taskText

codeagent-wrapper/internal/app/executor_alias.go

@@ -52,3 +52,11 @@ func runCodexProcess(parentCtx context.Context, codexArgs []string, taskText str
 func runCodexTaskWithContext(parentCtx context.Context, taskSpec TaskSpec, backend Backend, customArgs []string, useCustomArgs bool, silent bool, timeoutSec int) TaskResult {
 	return executor.RunCodexTaskWithContext(parentCtx, taskSpec, backend, codexCommand, buildCodexArgsFn, customArgs, useCustomArgs, silent, timeoutSec)
 }
+
+func detectProjectSkills(workDir string) []string {
+	return executor.DetectProjectSkills(workDir)
+}
+
+func resolveSkillContent(skills []string, maxBudget int) string {
+	return executor.ResolveSkillContent(skills, maxBudget)
+}