fix(session): use fmt.Fprintf with nolint to satisfy both staticcheck and errcheck

Reader agent scans session logs for SFT/DPO candidates; writer receives
reader output and formats+writes training pairs to brain/training-data/.
Adds trainer-reader.md and trainer-writer.md discipline prompts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/supervisor/main.go

@@ -13,6 +13,10 @@ import (
 	"github.com/mathiasbq/supervisor/internal/skills/brain"
 	"github.com/mathiasbq/supervisor/internal/skills/org"
 	"github.com/mathiasbq/supervisor/internal/skills/retrospective"
+	skilldebug "github.com/mathiasbq/supervisor/internal/skills/debug"
+	"github.com/mathiasbq/supervisor/internal/skills/review"
+	"github.com/mathiasbq/supervisor/internal/skills/spec"
+	"github.com/mathiasbq/supervisor/internal/skills/trainer"
 	"github.com/mathiasbq/supervisor/internal/skills/sessionlog"
 	"github.com/mathiasbq/supervisor/internal/skills/tdd"
 	"github.com/mathiasbq/supervisor/internal/tier"
@@ -51,6 +55,35 @@ func main() {
 		os.Exit(1)
 	}
 
+	reviewPrompt, err := os.ReadFile(cfg.ConfigDir + "/review.md")
+	if err != nil {
+		logger.Error("read review.md", "path", cfg.ConfigDir+"/review.md", "err", err)
+		os.Exit(1)
+	}
+
+	debugPrompt, err := os.ReadFile(cfg.ConfigDir + "/debug.md")
+	if err != nil {
+		logger.Error("read debug.md", "path", cfg.ConfigDir+"/debug.md", "err", err)
+		os.Exit(1)
+	}
+
+	specPrompt, err := os.ReadFile(cfg.ConfigDir + "/spec.md")
+	if err != nil {
+		logger.Error("read spec.md", "path", cfg.ConfigDir+"/spec.md", "err", err)
+		os.Exit(1)
+	}
+
+	trainerReaderPrompt, err := os.ReadFile(cfg.ConfigDir + "/trainer-reader.md")
+	if err != nil {
+		logger.Error("read trainer-reader.md", "path", cfg.ConfigDir+"/trainer-reader.md", "err", err)
+		os.Exit(1)
+	}
+	trainerWriterPrompt, err := os.ReadFile(cfg.ConfigDir + "/trainer-writer.md")
+	if err != nil {
+		logger.Error("read trainer-writer.md", "path", cfg.ConfigDir+"/trainer-writer.md", "err", err)
+		os.Exit(1)
+	}
+
 	executor := iexec.New(iexec.Config{
 		SystemPrompt:   string(systemPrompt),
 		LiteLLMBaseURL: cfg.LiteLLMBaseURL,
@@ -67,6 +100,7 @@ func main() {
 		SkillPrompt:  string(tddPrompt),
 		DefaultModel: models.Resolve("tdd", ""),
 		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
 	}))
 	reg.Register(brain.New(brain.Config{
 		IngestBaseURL: cfg.IngestBaseURL,
@@ -83,6 +117,32 @@ func main() {
 		SessionsDir:  cfg.SessionsDir,
 		ExecutorFn:   executor.Run,
 	}))
+	reg.Register(review.New(review.Config{
+		SkillPrompt:  string(reviewPrompt),
+		DefaultModel: models.Resolve("review", ""),
+		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
+	}))
+	reg.Register(skilldebug.New(skilldebug.Config{
+		SkillPrompt:  string(debugPrompt),
+		DefaultModel: models.Resolve("debug", ""),
+		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
+	}))
+	reg.Register(spec.New(spec.Config{
+		SkillPrompt:  string(specPrompt),
+		DefaultModel: models.Resolve("spec", ""),
+		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
+	}))
+	reg.Register(trainer.New(trainer.Config{
+		ReaderPrompt: string(trainerReaderPrompt),
+		WriterPrompt: string(trainerWriterPrompt),
+		DefaultModel: models.Resolve("trainer", ""),
+		ExecutorFn:   executor.Run,
+		SessionsDir:  cfg.SessionsDir,
+		BrainDir:     cfg.BrainDir,
+	}))
 
 	srv := mcp.NewServer(reg)
 	mux := http.NewServeMux()

config/models.yaml

@@ -9,3 +9,5 @@ skills:
   review:        ollama/devstral-tuned
   debug:         ollama/deepseek-r1-tuned
   retrospective: ollama/qwen3-coder-30b-tuned
+  spec:          ollama/qwen3-coder-30b-tuned
+  trainer:       ollama/qwen3-coder-30b-tuned

config/supervisor/debug.md

@@ -0,0 +1,31 @@
+# Debug Discipline
+
+You are a systematic debugger. Form hypotheses before suggesting fixes.
+
+## Iron laws
+1. Never suggest "try X and see what happens" — every hypothesis must have a specific expected outcome if correct
+2. Generate exactly 3-5 hypotheses, ordered by likelihood (most likely first)
+3. Never fix the bug — diagnose only; the caller decides what to do with the hypotheses
+
+## Output contract
+Return JSON result with:
+- `status`: "pass" (hypotheses generated) or "error" (error too ambiguous to analyse)
+- `phase`: "debug"
+- `skill`: "debug"
+- `file_path`: the most relevant file to the error (read it)
+- `runner_output`: your hypotheses, formatted as:
+  ```
+  HYPOTHESIS 1 (likelihood: high): <mechanism>
+  VERIFY: <exact command or file to check> → expected if correct: <specific output>
+
+  HYPOTHESIS 2 (likelihood: medium): <mechanism>
+  VERIFY: <exact command or file to check> → expected if correct: <specific output>
+  ```
+- `verified`: false — verification is the caller's job
+- `message`: "N hypotheses for: <one-line error summary>"
+
+## Rules
+1. Read the error and any context files provided before forming hypotheses
+2. Identify the failure mode first — what actually went wrong, not just what the error says
+3. For each hypothesis: name the mechanism, explain why it would produce this exact error, give a concrete verification command with expected output
+4. If the error is clearly a typo or trivial mistake, still form 3 hypotheses — surface the most likely cause as #1

config/supervisor/review.md

@@ -0,0 +1,30 @@
+# Code Review Discipline
+
+You are a disciplined code reviewer. Read files carefully before commenting.
+
+## Iron laws
+1. Never approve security vulnerabilities: command injection, SQL injection, credential exposure, path traversal, unchecked input at system boundaries
+2. Never approve silently swallowed errors — `err != nil` without wrapping or handling is always wrong
+3. Never approve missing validation at system boundaries (user input, external APIs, file reads)
+
+## Output contract
+Return JSON result with:
+- `status`: "pass" if no blocking issues; "fail" if any iron law is violated
+- `phase`: "review"
+- `skill`: "review"
+- `file_path`: first file reviewed
+- `runner_output`: full review formatted as:
+  ```
+  CRITICAL: <issue> at <file>:<line>
+  WARNING: <issue> at <file>:<line>
+  SUGGESTION: <issue> at <file>:<line>
+  ```
+- `verified`: true if you read all specified files; false if any were missing or unreadable
+- `message`: "N critical, M warnings, K suggestions" or "clean: <which iron law checks passed and why>"
+
+## Rules
+1. Read every file listed before writing feedback
+2. Check iron laws first — any violation is CRITICAL and sets status to "fail"
+3. Then check: correctness, test coverage for new code, Go style conventions
+4. Never rubber-stamp — if nothing is wrong, explain specifically which iron law checks you ran and why they passed
+5. Line references are required for every finding — "roughly around the middle" is not acceptable

config/supervisor/spec.md

@@ -0,0 +1,46 @@
+# Spec Writing Discipline
+
+You write structured implementation specs. Nothing is left ambiguous.
+
+## Iron laws
+1. Success criteria must be measurable — "the system is fast" is banned; "p99 < 200ms under 100 RPS" is valid
+2. Always include an explicit "Out of scope" section — if you don't draw the boundary, the developer will guess wrong
+3. Every technical decision in the approach must have a rationale
+
+## Output contract
+Return JSON result with:
+- `status`: "pass" (spec written) or "error" (requirements too ambiguous to spec without more input)
+- `phase`: "spec"
+- `skill`: "spec"
+- `file_path`: the output_path where the spec was written (absolute path)
+- `runner_output`: ""
+- `verified`: true if the file was written successfully
+- `message`: "spec written: <one-line summary of what was specced>"
+
+## Spec structure
+Write the spec as markdown to the output_path:
+
+```markdown
+# [Feature] Spec
+
+## Problem statement
+[What problem does this solve? For whom? Why now?]
+
+## Success criteria
+- [ ] [Criterion 1 — measurable and verifiable]
+- [ ] [Criterion 2 — measurable and verifiable]
+
+## Constraints
+[Non-negotiable requirements the solution must satisfy]
+
+## Out of scope
+[What we are explicitly NOT doing in this iteration]
+
+## Technical approach
+[Architecture decisions, key components, rationale for each choice]
+
+## Risks
+[What could go wrong, and how we'd mitigate it]
+```
+
+If the requirements are too vague to produce measurable success criteria, return status "error" with a message listing the specific questions that need answers.

config/supervisor/trainer-reader.md

@@ -0,0 +1,31 @@
+# Trainer Reader Discipline
+
+You scan session logs and identify candidate learning moments worth converting to training data.
+
+## What to look for
+- **SFT candidates**: the worker did exactly the right thing — a clean pattern worth reinforcing
+- **DPO candidates**: the worker first produced a wrong or suboptimal response, then corrected — you have both rejected and chosen
+
+## Scoring (1–5)
+- 5: novel pattern, clearly correct, generalises across projects
+- 4: good pattern, correct, somewhat project-specific but still useful
+- 3: correct but obvious — include only if especially clean
+- 2 or below: skip — too ambiguous or too context-specific
+
+## Output contract
+Return JSON result with:
+- `status`: "pass" or "error"
+- `phase`: "trainer"
+- `skill`: "trainer"
+- `file_path`: ""
+- `runner_output`: JSON array of candidates (valid JSON, not markdown):
+  [{"type":"sft","moment":"<what happened>","prompt":"<what was asked>","completion":"<what was done right>","score":4},
+   {"type":"dpo","moment":"<what happened>","prompt":"<what was asked>","chosen":"<correct>","rejected":"<incorrect>","score":3}]
+- `verified`: true
+- `message`: "N sft candidates, M dpo candidates found"
+
+## Rules
+1. Read all session entries in the task prompt
+2. Score each entry — only include entries scoring >= 3
+3. Prompt/completion fields must be phrased to generalise: no project-specific paths or names
+4. If no candidates score >= 3, return an empty array `[]` — never force low-quality candidates

config/supervisor/trainer-writer.md

@@ -0,0 +1,35 @@
+# Trainer Writer Discipline
+
+You receive candidate learning moments from the reader and write clean SFT/DPO training pairs.
+
+## Quality gate (apply before writing)
+- SFT: prompt must be phrased so it could come from any project, not just this one
+- DPO: chosen and rejected must be clearly distinguishable — skip if a reader can't tell which is better
+- Never include project-specific paths, variable names, or identifiers in any pair
+
+## Output contract
+Return JSON result with:
+- `status`: "pass" (pairs written or skipped due to quality) or "error" (candidates JSON was malformed)
+- `phase`: "trainer"
+- `skill`: "trainer"
+- `file_path`: path of the last file written (empty if nothing passed quality gate)
+- `runner_output`: "N SFT pairs written to brain/training-data/sft/, M DPO pairs to brain/training-data/dpo/" or "0 pairs passed quality gate"
+- `verified`: true if files were written; false if nothing passed
+- `message`: "N sft + M dpo pairs for session <id>" or "no pairs passed quality gate"
+
+## File format
+JSONL — one JSON object per line.
+
+SFT: `{"prompt": "...", "completion": "..."}`
+DPO: `{"prompt": "...", "chosen": "...", "rejected": "..."}`
+
+Write SFT to: `<brain_dir>/training-data/sft/<session_id>.jsonl`
+Write DPO to: `<brain_dir>/training-data/dpo/<session_id>.jsonl`
+
+Append to existing files if they exist (don't overwrite).
+
+## Rules
+1. Parse the `reader_candidates` JSON from the task prompt
+2. For each candidate: apply quality gate
+3. Write passing SFT candidates to sft JSONL, DPO candidates to dpo JSONL
+4. If nothing passes, return status "pass" with verified: false and message "no pairs passed quality gate"

internal/exec/result.go

@@ -10,7 +10,7 @@ import (
 // validates its own output before returning.
 type Result struct {
 	Status       string `json:"status"`        // pass | fail | error
-	Phase        string `json:"phase"`         // red | green | refactor
+	Phase        string `json:"phase"`         // red | green | refactor | retrospective | review | debug | spec | trainer
 	Skill        string `json:"skill"`         // tdd | review | ...
 	FilePath     string `json:"file_path"`     // absolute path to generated file
 	RunnerOutput string `json:"runner_output"` // raw stdout+stderr from test runner
@@ -25,6 +25,10 @@ var validPhases = map[string]bool{
 	"green":         true,
 	"refactor":      true,
 	"retrospective": true,
+	"review":        true,
+	"debug":         true,
+	"spec":          true,
+	"trainer":       true,
 }
 
 func (r Result) Validate() error {
@@ -33,7 +37,7 @@ func (r Result) Validate() error {
 		errs = append(errs, "status must be pass|fail|error, got: "+r.Status)
 	}
 	if !validPhases[r.Phase] {
-		errs = append(errs, "phase must be red|green|refactor, got: "+r.Phase)
+		errs = append(errs, "phase must be one of red|green|refactor|retrospective|review|debug|spec|trainer, got: "+r.Phase)
 	}
 	if r.Skill == "" {
 		errs = append(errs, "skill is required")
@@ -50,7 +54,7 @@ const Schema = `{
   "required": ["status","phase","skill","file_path","runner_output","verified","model_used","message"],
   "properties": {
     "status":        {"type": "string", "enum": ["pass","fail","error"]},
-    "phase":         {"type": "string", "enum": ["red","green","refactor"]},
+    "phase":         {"type": "string"},
     "skill":         {"type": "string"},
     "file_path":     {"type": "string"},
     "runner_output": {"type": "string"},

internal/exec/result_test.go

@@ -69,3 +69,11 @@ func TestResultValidation(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateAcceptsAllPhases(t *testing.T) {
+	phases := []string{"red", "green", "refactor", "retrospective", "review", "debug", "spec", "trainer"}
+	for _, phase := range phases {
+		r := exec.Result{Status: "pass", Phase: phase, Skill: "test", ModelUsed: "self", Message: "ok"}
+		assert.NoError(t, r.Validate(), "phase %q should be valid", phase)
+	}
+}

internal/session/history.go

@@ -0,0 +1,38 @@
+// internal/session/history.go
+package session
+
+import (
+	"fmt"
+	"strings"
+)
+
+// FormatHistory formats prior session entries as a structured block for
+// injection into a worker task prompt. Entries matching excludePhase are
+// omitted (pass the current phase to avoid circular injection).
+func FormatHistory(entries []Entry, excludePhase string) string {
+	var filtered []Entry
+	for _, e := range entries {
+		if e.Phase != excludePhase {
+			filtered = append(filtered, e)
+		}
+	}
+	if len(filtered) == 0 {
+		return ""
+	}
+
+	var b strings.Builder
+	b.WriteString("## Session history\n\n")
+	for _, e := range filtered {
+		fmt.Fprintf(&b, "### Phase: %s\n", e.Phase)      //nolint:errcheck // strings.Builder never errors
+		fmt.Fprintf(&b, "- Skill: %s\n", e.Skill)        //nolint:errcheck
+		fmt.Fprintf(&b, "- Status: %s\n", e.FinalStatus) //nolint:errcheck
+		if e.FilePath != "" {
+			fmt.Fprintf(&b, "- File: %s\n", e.FilePath) //nolint:errcheck
+		}
+		if e.Message != "" {
+			fmt.Fprintf(&b, "- Summary: %s\n", e.Message) //nolint:errcheck
+		}
+		b.WriteString("\n")
+	}
+	return b.String()
+}

internal/session/history_test.go

@@ -0,0 +1,41 @@
+// internal/session/history_test.go
+package session_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/mathiasbq/supervisor/internal/session"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFormatHistoryEmpty(t *testing.T) {
+	result := session.FormatHistory(nil, "")
+	assert.Equal(t, "", result)
+}
+
+func TestFormatHistoryFormatsEntries(t *testing.T) {
+	entries := []session.Entry{
+		{
+			Skill: "tdd", Phase: "red", FinalStatus: "pass",
+			FilePath: "internal/foo/foo_test.go",
+			Message:  "wrote failing test for Foo",
+			Timestamp: time.Now(),
+		},
+	}
+	result := session.FormatHistory(entries, "")
+	assert.Contains(t, result, "## Session history")
+	assert.Contains(t, result, "Phase: red")
+	assert.Contains(t, result, "wrote failing test for Foo")
+	assert.Contains(t, result, "internal/foo/foo_test.go")
+}
+
+func TestFormatHistoryExcludesCurrentPhase(t *testing.T) {
+	entries := []session.Entry{
+		{Skill: "tdd", Phase: "red", Message: "red done", FinalStatus: "pass"},
+		{Skill: "tdd", Phase: "green", Message: "green done", FinalStatus: "pass"},
+	}
+	result := session.FormatHistory(entries, "green")
+	assert.Contains(t, result, "red done")
+	assert.NotContains(t, result, "green done")
+}

internal/skills/debug/handlers.go

@@ -0,0 +1,80 @@
+// internal/skills/debug/handlers.go
+package debug
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
+)
+
+type debugArgs struct {
+	ProjectRoot string `json:"project_root"`
+	Error       string `json:"error"`
+	Context     string `json:"context"`
+	Model       string `json:"model"`
+	SessionID   string `json:"session_id"`
+}
+
+// Handle dispatches the MCP tool call to the appropriate handler.
+func (s *Skill) Handle(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
+	if tool != "debug" {
+		return nil, fmt.Errorf("unknown tool: %s", tool)
+	}
+	var a debugArgs
+	if err := json.Unmarshal(args, &a); err != nil {
+		return nil, fmt.Errorf("parse args: %w", err)
+	}
+	if a.ProjectRoot == "" {
+		return nil, fmt.Errorf("project_root is required")
+	}
+	if a.Error == "" {
+		return nil, fmt.Errorf("error is required")
+	}
+
+	model := a.Model
+	if model == "" {
+		model = s.cfg.DefaultModel
+	}
+
+	task := fmt.Sprintf(
+		"phase: debug\nproject_root: %s\nerror: %s\ncontext: %s\nmodel: %s",
+		a.ProjectRoot, a.Error, a.Context, model,
+	)
+	task = s.prependHistory(a.SessionID, "debug", task)
+
+	if s.cfg.ExecutorFn == nil {
+		return nil, fmt.Errorf("no executor configured")
+	}
+	result, err := s.cfg.ExecutorFn(ctx, iexec.Request{
+		SkillPrompt: s.cfg.SkillPrompt,
+		TaskPrompt:  task,
+		Model:       model,
+		Tools:       "Read,Bash",
+	})
+	if err != nil {
+		return nil, err
+	}
+	b, err := json.Marshal(result)
+	if err != nil {
+		return nil, fmt.Errorf("marshal result: %w", err)
+	}
+	return b, nil
+}
+
+func (s *Skill) prependHistory(sessionID, currentPhase, task string) string {
+	if sessionID == "" || s.cfg.SessionsDir == "" {
+		return task
+	}
+	entries, err := session.Read(s.cfg.SessionsDir, sessionID)
+	if err != nil || len(entries) == 0 {
+		return task
+	}
+	history := session.FormatHistory(entries, currentPhase)
+	if history == "" {
+		return task
+	}
+	return history + "\n---\n\n" + task
+}

internal/skills/debug/handlers_test.go

@@ -0,0 +1,61 @@
+// internal/skills/debug/handlers_test.go
+package debug_test
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/skills/debug"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDebugToolRegistered(t *testing.T) {
+	sk := debug.New(debug.Config{SkillPrompt: "debug rules"})
+	names := make([]string, 0)
+	for _, tool := range sk.Tools() {
+		names = append(names, tool.Name)
+	}
+	assert.Contains(t, names, "debug")
+}
+
+func TestDebugRequiresProjectRoot(t *testing.T) {
+	sk := debug.New(debug.Config{SkillPrompt: "d"})
+	_, err := sk.Handle(context.Background(), "debug", json.RawMessage(`{"error":"panic: nil pointer"}`))
+	assert.ErrorContains(t, err, "project_root")
+}
+
+func TestDebugRequiresError(t *testing.T) {
+	sk := debug.New(debug.Config{SkillPrompt: "d"})
+	_, err := sk.Handle(context.Background(), "debug", json.RawMessage(`{"project_root":"/tmp"}`))
+	assert.ErrorContains(t, err, "error")
+}
+
+func TestDebugCallsExecutor(t *testing.T) {
+	called := false
+	var capturedTask string
+	fakeFn := func(_ context.Context, req iexec.Request) (iexec.Result, error) {
+		called = true
+		capturedTask = req.TaskPrompt
+		return iexec.Result{
+			Status: "pass", Phase: "debug", Skill: "debug",
+			RunnerOutput: "HYPOTHESIS 1 (likelihood: high): nil map access\nVERIFY: go test ./... → expected: panic line reference",
+			Verified:     false, ModelUsed: "self", Message: "3 hypotheses for: panic nil pointer at foo.go:42",
+		}, nil
+	}
+
+	sk := debug.New(debug.Config{SkillPrompt: "debug rules", ExecutorFn: fakeFn, SessionsDir: t.TempDir()})
+	out, err := sk.Handle(context.Background(), "debug", json.RawMessage(
+		`{"project_root":"/tmp/proj","error":"panic: nil pointer dereference at foo.go:42","context":"occurs on startup"}`,
+	))
+	require.NoError(t, err)
+	assert.True(t, called)
+	assert.Contains(t, capturedTask, "panic: nil pointer dereference")
+	assert.Contains(t, capturedTask, "occurs on startup")
+
+	var result iexec.Result
+	require.NoError(t, json.Unmarshal(out, &result))
+	assert.Equal(t, "debug", result.Phase)
+}

internal/skills/debug/skill.go

@@ -0,0 +1,55 @@
+// internal/skills/debug/skill.go
+package debug
+
+import (
+	"context"
+	"encoding/json"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/registry"
+)
+
+// ExecutorFn is the function signature for running a worker subprocess.
+type ExecutorFn func(ctx context.Context, req iexec.Request) (iexec.Result, error)
+
+// Config holds dependencies for the debug skill.
+type Config struct {
+	SkillPrompt  string
+	DefaultModel string
+	ExecutorFn   ExecutorFn
+	SessionsDir  string
+}
+
+// Skill implements the debug MCP tool.
+type Skill struct{ cfg Config }
+
+// New creates a new debug Skill.
+func New(cfg Config) *Skill { return &Skill{cfg: cfg} }
+
+// Name returns the skill identifier.
+func (s *Skill) Name() string { return "debug" }
+
+// Tools returns the MCP tool definitions for this skill.
+func (s *Skill) Tools() []registry.ToolDef {
+	schema := func(required []string, props map[string]any) json.RawMessage {
+		b, _ := json.Marshal(map[string]any{"type": "object", "required": required, "properties": props})
+		return b
+	}
+	str := map[string]any{"type": "string"}
+	return []registry.ToolDef{
+		{
+			Name:        "debug",
+			Description: "Analyse an error and return 3-5 hypotheses ordered by likelihood, each with a concrete verification step.",
+			InputSchema: schema(
+				[]string{"project_root", "error"},
+				map[string]any{
+					"project_root": str,
+					"error":        str,
+					"context":      str,
+					"model":        str,
+					"session_id":   str,
+				},
+			),
+		},
+	}
+}

internal/skills/review/handlers.go

@@ -0,0 +1,81 @@
+// internal/skills/review/handlers.go
+package review
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
+)
+
+type reviewArgs struct {
+	ProjectRoot string   `json:"project_root"`
+	Files       []string `json:"files"`
+	Context     string   `json:"context"`
+	Model       string   `json:"model"`
+	SessionID   string   `json:"session_id"`
+}
+
+// Handle dispatches the MCP tool call to the appropriate handler.
+func (s *Skill) Handle(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
+	if tool != "review" {
+		return nil, fmt.Errorf("unknown tool: %s", tool)
+	}
+	var a reviewArgs
+	if err := json.Unmarshal(args, &a); err != nil {
+		return nil, fmt.Errorf("parse args: %w", err)
+	}
+	if a.ProjectRoot == "" {
+		return nil, fmt.Errorf("project_root is required")
+	}
+	if len(a.Files) == 0 {
+		return nil, fmt.Errorf("files is required")
+	}
+
+	model := a.Model
+	if model == "" {
+		model = s.cfg.DefaultModel
+	}
+
+	task := fmt.Sprintf(
+		"phase: review\nproject_root: %s\nfiles: %s\ncontext: %s\nmodel: %s",
+		a.ProjectRoot, strings.Join(a.Files, ", "), a.Context, model,
+	)
+	task = s.prependHistory(a.SessionID, "review", task)
+
+	if s.cfg.ExecutorFn == nil {
+		return nil, fmt.Errorf("no executor configured")
+	}
+	result, err := s.cfg.ExecutorFn(ctx, iexec.Request{
+		SkillPrompt: s.cfg.SkillPrompt,
+		TaskPrompt:  task,
+		Model:       model,
+		Tools:       "Read,Bash",
+	})
+	if err != nil {
+		return nil, err
+	}
+	b, err := json.Marshal(result)
+	if err != nil {
+		return nil, fmt.Errorf("marshal result: %w", err)
+	}
+	return b, nil
+}
+
+func (s *Skill) prependHistory(sessionID, currentPhase, task string) string {
+	if sessionID == "" || s.cfg.SessionsDir == "" {
+		return task
+	}
+	entries, err := session.Read(s.cfg.SessionsDir, sessionID)
+	if err != nil || len(entries) == 0 {
+		return task
+	}
+	history := session.FormatHistory(entries, currentPhase)
+	if history == "" {
+		return task
+	}
+	return history + "\n---\n\n" + task
+}

internal/skills/review/handlers_test.go

@@ -0,0 +1,61 @@
+// internal/skills/review/handlers_test.go
+package review_test
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/skills/review"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReviewToolRegistered(t *testing.T) {
+	sk := review.New(review.Config{SkillPrompt: "review rules"})
+	names := make([]string, 0)
+	for _, tool := range sk.Tools() {
+		names = append(names, tool.Name)
+	}
+	assert.Contains(t, names, "review")
+}
+
+func TestReviewRequiresProjectRoot(t *testing.T) {
+	sk := review.New(review.Config{SkillPrompt: "r"})
+	_, err := sk.Handle(context.Background(), "review", json.RawMessage(`{"files":["main.go"]}`))
+	assert.ErrorContains(t, err, "project_root")
+}
+
+func TestReviewRequiresFiles(t *testing.T) {
+	sk := review.New(review.Config{SkillPrompt: "r"})
+	_, err := sk.Handle(context.Background(), "review", json.RawMessage(`{"project_root":"/tmp"}`))
+	assert.ErrorContains(t, err, "files")
+}
+
+func TestReviewCallsExecutor(t *testing.T) {
+	called := false
+	var capturedTask string
+	fakeFn := func(_ context.Context, req iexec.Request) (iexec.Result, error) {
+		called = true
+		capturedTask = req.TaskPrompt
+		return iexec.Result{
+			Status: "pass", Phase: "review", Skill: "review",
+			Verified: true, ModelUsed: "self", Message: "2 warnings found",
+		}, nil
+	}
+
+	sk := review.New(review.Config{SkillPrompt: "review rules", ExecutorFn: fakeFn, SessionsDir: t.TempDir()})
+	out, err := sk.Handle(context.Background(), "review", json.RawMessage(
+		`{"project_root":"/tmp/proj","files":["internal/foo/foo.go"],"context":"PR: add Foo helper"}`,
+	))
+	require.NoError(t, err)
+	assert.True(t, called)
+	assert.Contains(t, capturedTask, "internal/foo/foo.go")
+	assert.Contains(t, capturedTask, "PR: add Foo helper")
+
+	var result iexec.Result
+	require.NoError(t, json.Unmarshal(out, &result))
+	assert.Equal(t, "pass", result.Status)
+	assert.Equal(t, "review", result.Phase)
+}

internal/skills/review/skill.go

@@ -0,0 +1,55 @@
+// internal/skills/review/skill.go
+package review
+
+import (
+	"context"
+	"encoding/json"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/registry"
+)
+
+// ExecutorFn is the function signature for running a worker subprocess.
+type ExecutorFn func(ctx context.Context, req iexec.Request) (iexec.Result, error)
+
+// Config holds dependencies for the review skill.
+type Config struct {
+	SkillPrompt  string
+	DefaultModel string
+	ExecutorFn   ExecutorFn
+	SessionsDir  string
+}
+
+// Skill implements the review MCP tool.
+type Skill struct{ cfg Config }
+
+// New creates a new review Skill.
+func New(cfg Config) *Skill { return &Skill{cfg: cfg} }
+
+// Name returns the skill identifier.
+func (s *Skill) Name() string { return "review" }
+
+// Tools returns the MCP tool definitions for this skill.
+func (s *Skill) Tools() []registry.ToolDef {
+	schema := func(required []string, props map[string]any) json.RawMessage {
+		b, _ := json.Marshal(map[string]any{"type": "object", "required": required, "properties": props})
+		return b
+	}
+	str := map[string]any{"type": "string"}
+	return []registry.ToolDef{
+		{
+			Name:        "review",
+			Description: "Perform a structured code review of the specified files. Returns findings with severity levels.",
+			InputSchema: schema(
+				[]string{"project_root", "files"},
+				map[string]any{
+					"project_root": str,
+					"files":        map[string]any{"type": "array", "items": map[string]any{"type": "string"}},
+					"context":      str,
+					"model":        str,
+					"session_id":   str,
+				},
+			),
+		},
+	}
+}

internal/skills/spec/handlers.go

@@ -0,0 +1,85 @@
+// internal/skills/spec/handlers.go
+package spec
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
+)
+
+type specArgs struct {
+	ProjectRoot  string `json:"project_root"`
+	Requirements string `json:"requirements"`
+	OutputPath   string `json:"output_path"`
+	Context      string `json:"context"`
+	Model        string `json:"model"`
+	SessionID    string `json:"session_id"`
+}
+
+// Handle dispatches the MCP tool call to the appropriate handler.
+func (s *Skill) Handle(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
+	if tool != "spec" {
+		return nil, fmt.Errorf("unknown tool: %s", tool)
+	}
+	var a specArgs
+	if err := json.Unmarshal(args, &a); err != nil {
+		return nil, fmt.Errorf("parse args: %w", err)
+	}
+	if a.ProjectRoot == "" {
+		return nil, fmt.Errorf("project_root is required")
+	}
+	if a.Requirements == "" {
+		return nil, fmt.Errorf("requirements is required")
+	}
+	outputPath := a.OutputPath
+	if outputPath == "" {
+		outputPath = "docs/spec.md"
+	}
+
+	model := a.Model
+	if model == "" {
+		model = s.cfg.DefaultModel
+	}
+
+	task := fmt.Sprintf(
+		"phase: spec\nproject_root: %s\nrequirements: %s\noutput_path: %s\ncontext: %s\nmodel: %s",
+		a.ProjectRoot, a.Requirements, outputPath, a.Context, model,
+	)
+	task = s.prependHistory(a.SessionID, "spec", task)
+
+	if s.cfg.ExecutorFn == nil {
+		return nil, fmt.Errorf("no executor configured")
+	}
+	result, err := s.cfg.ExecutorFn(ctx, iexec.Request{
+		SkillPrompt: s.cfg.SkillPrompt,
+		TaskPrompt:  task,
+		Model:       model,
+		Tools:       "Read,Write",
+	})
+	if err != nil {
+		return nil, err
+	}
+	b, err := json.Marshal(result)
+	if err != nil {
+		return nil, fmt.Errorf("marshal result: %w", err)
+	}
+	return b, nil
+}
+
+func (s *Skill) prependHistory(sessionID, currentPhase, task string) string {
+	if sessionID == "" || s.cfg.SessionsDir == "" {
+		return task
+	}
+	entries, err := session.Read(s.cfg.SessionsDir, sessionID)
+	if err != nil || len(entries) == 0 {
+		return task
+	}
+	history := session.FormatHistory(entries, currentPhase)
+	if history == "" {
+		return task
+	}
+	return history + "\n---\n\n" + task
+}

internal/skills/spec/handlers_test.go

@@ -0,0 +1,61 @@
+// internal/skills/spec/handlers_test.go
+package spec_test
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/skills/spec"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSpecToolRegistered(t *testing.T) {
+	sk := spec.New(spec.Config{SkillPrompt: "spec rules"})
+	names := make([]string, 0)
+	for _, tool := range sk.Tools() {
+		names = append(names, tool.Name)
+	}
+	assert.Contains(t, names, "spec")
+}
+
+func TestSpecRequiresProjectRoot(t *testing.T) {
+	sk := spec.New(spec.Config{SkillPrompt: "s"})
+	_, err := sk.Handle(context.Background(), "spec", json.RawMessage(`{"requirements":"add login"}`))
+	assert.ErrorContains(t, err, "project_root")
+}
+
+func TestSpecRequiresRequirements(t *testing.T) {
+	sk := spec.New(spec.Config{SkillPrompt: "s"})
+	_, err := sk.Handle(context.Background(), "spec", json.RawMessage(`{"project_root":"/tmp"}`))
+	assert.ErrorContains(t, err, "requirements")
+}
+
+func TestSpecCallsExecutor(t *testing.T) {
+	called := false
+	var capturedTask string
+	fakeFn := func(_ context.Context, req iexec.Request) (iexec.Result, error) {
+		called = true
+		capturedTask = req.TaskPrompt
+		return iexec.Result{
+			Status: "pass", Phase: "spec", Skill: "spec",
+			FilePath: "/tmp/proj/docs/login-spec.md",
+			Verified: true, ModelUsed: "self", Message: "spec written: login feature",
+		}, nil
+	}
+
+	sk := spec.New(spec.Config{SkillPrompt: "spec rules", ExecutorFn: fakeFn, SessionsDir: t.TempDir()})
+	out, err := sk.Handle(context.Background(), "spec", json.RawMessage(
+		`{"project_root":"/tmp/proj","requirements":"add OAuth2 login","output_path":"docs/login-spec.md"}`,
+	))
+	require.NoError(t, err)
+	assert.True(t, called)
+	assert.Contains(t, capturedTask, "OAuth2 login")
+	assert.Contains(t, capturedTask, "docs/login-spec.md")
+
+	var result iexec.Result
+	require.NoError(t, json.Unmarshal(out, &result))
+	assert.Equal(t, "spec", result.Phase)
+}

internal/skills/spec/skill.go

@@ -0,0 +1,56 @@
+// internal/skills/spec/skill.go
+package spec
+
+import (
+	"context"
+	"encoding/json"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/registry"
+)
+
+// ExecutorFn is the function signature for running a worker subprocess.
+type ExecutorFn func(ctx context.Context, req iexec.Request) (iexec.Result, error)
+
+// Config holds dependencies for the spec skill.
+type Config struct {
+	SkillPrompt  string
+	DefaultModel string
+	ExecutorFn   ExecutorFn
+	SessionsDir  string
+}
+
+// Skill implements the spec MCP tool.
+type Skill struct{ cfg Config }
+
+// New creates a new spec Skill.
+func New(cfg Config) *Skill { return &Skill{cfg: cfg} }
+
+// Name returns the skill identifier.
+func (s *Skill) Name() string { return "spec" }
+
+// Tools returns the MCP tool definitions for this skill.
+func (s *Skill) Tools() []registry.ToolDef {
+	schema := func(required []string, props map[string]any) json.RawMessage {
+		b, _ := json.Marshal(map[string]any{"type": "object", "required": required, "properties": props})
+		return b
+	}
+	str := map[string]any{"type": "string"}
+	return []registry.ToolDef{
+		{
+			Name:        "spec",
+			Description: "Generate a structured implementation spec from requirements. Writes the spec to output_path in the project.",
+			InputSchema: schema(
+				[]string{"project_root", "requirements"},
+				map[string]any{
+					"project_root": str,
+					"requirements": str,
+					"output_path":  str,
+					"context":      str,
+					"model":        str,
+					"session_id":   str,
+				},
+			),
+		},
+	}
+}

internal/skills/tdd/handlers.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 
 	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
 )
 
 func (s *Skill) Handle(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
@@ -51,6 +52,7 @@ type greenArgs struct {
 	TestPath    string `json:"test_path"`
 	Model       string `json:"model"`
 	TestCmd     string `json:"test_cmd"`
+	SessionID   string `json:"session_id"`
 }
 
 func (s *Skill) handleGreen(ctx context.Context, raw json.RawMessage) (json.RawMessage, error) {
@@ -68,6 +70,7 @@ func (s *Skill) handleGreen(ctx context.Context, raw json.RawMessage) (json.RawM
 		"phase: green\nproject_root: %s\ntest_path: %s\nmodel: %s\ntest_cmd: %s",
 		args.ProjectRoot, args.TestPath, s.resolveModel(args.Model), args.TestCmd,
 	)
+	task = s.prependHistory(args.SessionID, "green", task)
 	return s.execute(ctx, task)
 }
 
@@ -77,6 +80,7 @@ type refactorArgs struct {
 	ImplPath    string `json:"impl_path"`
 	Model       string `json:"model"`
 	TestCmd     string `json:"test_cmd"`
+	SessionID   string `json:"session_id"`
 }
 
 func (s *Skill) handleRefactor(ctx context.Context, raw json.RawMessage) (json.RawMessage, error) {
@@ -97,9 +101,25 @@ func (s *Skill) handleRefactor(ctx context.Context, raw json.RawMessage) (json.R
 		"phase: refactor\nproject_root: %s\ntest_path: %s\nimpl_path: %s\nmodel: %s\ntest_cmd: %s",
 		args.ProjectRoot, args.TestPath, args.ImplPath, s.resolveModel(args.Model), args.TestCmd,
 	)
+	task = s.prependHistory(args.SessionID, "refactor", task)
 	return s.execute(ctx, task)
 }
 
+func (s *Skill) prependHistory(sessionID, currentPhase, task string) string {
+	if sessionID == "" || s.cfg.SessionsDir == "" {
+		return task
+	}
+	entries, err := session.Read(s.cfg.SessionsDir, sessionID)
+	if err != nil || len(entries) == 0 {
+		return task
+	}
+	history := session.FormatHistory(entries, currentPhase)
+	if history == "" {
+		return task
+	}
+	return history + "\n---\n\n" + task
+}
+
 func (s *Skill) resolveModel(override string) string {
 	if override != "" {
 		return override

internal/skills/tdd/handlers_test.go

@@ -5,6 +5,8 @@ import (
 	"encoding/json"
 	"testing"
 
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
 	"github.com/mathiasbq/supervisor/internal/skills/tdd"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -41,5 +43,43 @@ func TestTDDRedRequiresSpec(t *testing.T) {
 	assert.ErrorContains(t, err, "spec")
 }
 
+func TestTDDGreenInjectsSessionHistory(t *testing.T) {
+	sessDir := t.TempDir()
+	require.NoError(t, session.Append(sessDir, "sess-1", session.Entry{
+		SessionID: "sess-1", Skill: "tdd", Phase: "red", FinalStatus: "pass",
+		FilePath: "internal/foo/foo_test.go",
+		Message:  "wrote failing test for Foo",
+	}))
+
+	var capturedPrompt string
+	fakeFn := func(_ context.Context, req iexec.Request) (iexec.Result, error) {
+		capturedPrompt = req.TaskPrompt
+		return iexec.Result{Status: "pass", Phase: "green", Skill: "tdd", Verified: true, ModelUsed: "self", Message: "ok"}, nil
+	}
+
+	sk := tdd.New(tdd.Config{SkillPrompt: "tdd", ExecutorFn: fakeFn, SessionsDir: sessDir})
+	_, err := sk.Handle(context.Background(), "tdd_green", json.RawMessage(
+		`{"project_root":"/tmp","test_path":"internal/foo/foo_test.go","test_cmd":"go test ./...","session_id":"sess-1"}`,
+	))
+	require.NoError(t, err)
+	assert.Contains(t, capturedPrompt, "## Session history")
+	assert.Contains(t, capturedPrompt, "wrote failing test for Foo")
+}
+
+func TestTDDGreenNoHistoryWhenSessionIDEmpty(t *testing.T) {
+	var capturedPrompt string
+	fakeFn := func(_ context.Context, req iexec.Request) (iexec.Result, error) {
+		capturedPrompt = req.TaskPrompt
+		return iexec.Result{Status: "pass", Phase: "green", Skill: "tdd", Verified: true, ModelUsed: "self", Message: "ok"}, nil
+	}
+
+	sk := tdd.New(tdd.Config{SkillPrompt: "tdd", ExecutorFn: fakeFn, SessionsDir: t.TempDir()})
+	_, err := sk.Handle(context.Background(), "tdd_green", json.RawMessage(
+		`{"project_root":"/tmp","test_path":"internal/foo/foo_test.go"}`,
+	))
+	require.NoError(t, err)
+	assert.NotContains(t, capturedPrompt, "## Session history")
+}
+
 // Ensure require is used (avoids import error).
 var _ = require.New

internal/skills/tdd/skill.go

@@ -16,6 +16,7 @@ type Config struct {
 	SkillPrompt  string
 	ExecutorFn   ExecutorFn // nil = no executor (tests that don't reach execute())
 	DefaultModel string
+	SessionsDir  string // optional: path to brain/sessions/ for history injection
 }
 
 type Skill struct {
@@ -63,6 +64,7 @@ func (s *Skill) Tools() []registry.ToolDef {
 					"test_path":    strProp,
 					"model":        strProp,
 					"test_cmd":     strProp,
+					"session_id":   strProp,
 				},
 			),
 		},
@@ -77,6 +79,7 @@ func (s *Skill) Tools() []registry.ToolDef {
 					"impl_path":    strProp,
 					"model":        strProp,
 					"test_cmd":     strProp,
+					"session_id":   strProp,
 				},
 			),
 		},

internal/skills/trainer/handlers.go

@@ -0,0 +1,80 @@
+// internal/skills/trainer/handlers.go
+package trainer
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
+)
+
+type trainArgs struct {
+	SessionID string `json:"session_id"`
+	Model     string `json:"model"`
+}
+
+// Handle dispatches the MCP tool call to the trainer handler.
+func (s *Skill) Handle(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
+	if tool != "trainer" {
+		return nil, fmt.Errorf("unknown tool: %s", tool)
+	}
+	var a trainArgs
+	if err := json.Unmarshal(args, &a); err != nil {
+		return nil, fmt.Errorf("parse args: %w", err)
+	}
+	if a.SessionID == "" {
+		return nil, fmt.Errorf("session_id is required")
+	}
+	if s.cfg.ExecutorFn == nil {
+		return nil, fmt.Errorf("no executor configured")
+	}
+
+	model := a.Model
+	if model == "" {
+		model = s.cfg.DefaultModel
+	}
+
+	entries, err := session.Read(s.cfg.SessionsDir, a.SessionID)
+	if err != nil {
+		return nil, fmt.Errorf("read session log: %w", err)
+	}
+
+	// ── Step 1: Reader agent ─────────────────────────────────────────────────
+	history := session.FormatHistory(entries, "")
+	readerTask := fmt.Sprintf(
+		"role: reader\nsession_id: %s\nbrain_dir: %s\n\n%s",
+		a.SessionID, s.cfg.BrainDir, history,
+	)
+	readerResult, err := s.cfg.ExecutorFn(ctx, iexec.Request{
+		SkillPrompt: s.cfg.ReaderPrompt,
+		TaskPrompt:  readerTask,
+		Model:       model,
+		Tools:       "Read",
+	})
+	if err != nil {
+		return nil, fmt.Errorf("reader agent: %w", err)
+	}
+
+	// ── Step 2: Writer agent (receives reader candidates) ────────────────────
+	writerTask := fmt.Sprintf(
+		"role: writer\nsession_id: %s\nbrain_dir: %s\n\nreader_summary: %s\nreader_candidates:\n%s",
+		a.SessionID, s.cfg.BrainDir, readerResult.Message, readerResult.RunnerOutput,
+	)
+	writerResult, err := s.cfg.ExecutorFn(ctx, iexec.Request{
+		SkillPrompt: s.cfg.WriterPrompt,
+		TaskPrompt:  writerTask,
+		Model:       model,
+		Tools:       "Read,Write",
+	})
+	if err != nil {
+		return nil, fmt.Errorf("writer agent: %w", err)
+	}
+
+	b, err := json.Marshal(writerResult)
+	if err != nil {
+		return nil, fmt.Errorf("marshal result: %w", err)
+	}
+	return b, nil
+}

internal/skills/trainer/handlers_test.go

@@ -0,0 +1,82 @@
+// internal/skills/trainer/handlers_test.go
+package trainer_test
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/session"
+	"github.com/mathiasbq/supervisor/internal/skills/trainer"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTrainerToolRegistered(t *testing.T) {
+	sk := trainer.New(trainer.Config{ReaderPrompt: "r", WriterPrompt: "w"})
+	names := make([]string, 0)
+	for _, tool := range sk.Tools() {
+		names = append(names, tool.Name)
+	}
+	assert.Contains(t, names, "trainer")
+}
+
+func TestTrainerRequiresSessionID(t *testing.T) {
+	sk := trainer.New(trainer.Config{ReaderPrompt: "r", WriterPrompt: "w"})
+	_, err := sk.Handle(context.Background(), "trainer", json.RawMessage(`{}`))
+	assert.ErrorContains(t, err, "session_id")
+}
+
+func TestTrainerCallsReaderThenWriter(t *testing.T) {
+	sessDir := t.TempDir()
+	require.NoError(t, session.Append(sessDir, "sess-1", session.Entry{
+		SessionID: "sess-1", Skill: "tdd", Phase: "red", FinalStatus: "pass",
+		Message: "wrote failing test", FilePath: "internal/foo/foo_test.go",
+	}))
+
+	callCount := 0
+	var readerTask, writerTask string
+
+	fakeFn := func(_ context.Context, req iexec.Request) (iexec.Result, error) {
+		callCount++
+		if callCount == 1 {
+			// reader call
+			readerTask = req.TaskPrompt
+			return iexec.Result{
+				Status: "pass", Phase: "trainer", Skill: "trainer",
+				RunnerOutput: `[{"type":"sft","moment":"first-pass clean TDD","score":4}]`,
+				Verified: true, ModelUsed: "self", Message: "1 sft candidate found",
+			}, nil
+		}
+		// writer call
+		writerTask = req.TaskPrompt
+		return iexec.Result{
+			Status: "pass", Phase: "trainer", Skill: "trainer",
+			FilePath: sessDir + "/training-data/sft/sess-1.jsonl",
+			Verified: true, ModelUsed: "self", Message: "1 sft pair written",
+		}, nil
+	}
+
+	sk := trainer.New(trainer.Config{
+		ReaderPrompt: "reader rules",
+		WriterPrompt: "writer rules",
+		ExecutorFn:   fakeFn,
+		SessionsDir:  sessDir,
+		BrainDir:     t.TempDir(),
+	})
+	out, err := sk.Handle(context.Background(), "trainer", json.RawMessage(`{"session_id":"sess-1"}`))
+	require.NoError(t, err)
+
+	assert.Equal(t, 2, callCount, "executor must be called exactly twice: reader then writer")
+	assert.Contains(t, readerTask, "role: reader")
+	assert.Contains(t, readerTask, "sess-1")
+	assert.Contains(t, readerTask, "wrote failing test") // session history in reader prompt
+	assert.Contains(t, writerTask, "role: writer")
+	assert.Contains(t, writerTask, "sft candidate") // reader output passed to writer
+
+	var result iexec.Result
+	require.NoError(t, json.Unmarshal(out, &result))
+	assert.Equal(t, "trainer", result.Phase)
+	assert.Equal(t, "pass", result.Status)
+}

internal/skills/trainer/skill.go

@@ -0,0 +1,53 @@
+// internal/skills/trainer/skill.go
+package trainer
+
+import (
+	"context"
+	"encoding/json"
+
+	iexec "github.com/mathiasbq/supervisor/internal/exec"
+	"github.com/mathiasbq/supervisor/internal/registry"
+)
+
+// ExecutorFn is the function signature for running a worker subprocess.
+type ExecutorFn func(ctx context.Context, req iexec.Request) (iexec.Result, error)
+
+// Config holds dependencies for the trainer skill.
+type Config struct {
+	ReaderPrompt string
+	WriterPrompt string
+	DefaultModel string
+	ExecutorFn   ExecutorFn
+	SessionsDir  string
+	BrainDir     string // root of brain/ directory; writer writes to BrainDir/training-data/
+}
+
+// Skill implements the trainer MCP tool.
+type Skill struct{ cfg Config }
+
+// New creates a new trainer Skill.
+func New(cfg Config) *Skill { return &Skill{cfg: cfg} }
+
+// Name returns the skill identifier.
+func (s *Skill) Name() string { return "trainer" }
+
+// Tools returns the MCP tool definitions for this skill.
+func (s *Skill) Tools() []registry.ToolDef {
+	schema := func(required []string, props map[string]any) json.RawMessage {
+		b, _ := json.Marshal(map[string]any{"type": "object", "required": required, "properties": props})
+		return b
+	}
+	return []registry.ToolDef{
+		{
+			Name:        "trainer",
+			Description: "Extract SFT and DPO training pairs from a session log. Runs a reader→writer chain: reader identifies learning moments, writer formats and writes pairs to brain/training-data/.",
+			InputSchema: schema(
+				[]string{"session_id"},
+				map[string]any{
+					"session_id": map[string]any{"type": "string"},
+					"model":      map[string]any{"type": "string"},
+				},
+			),
+		},
+	}
+}