fix: fold in PR #5 review findings (thinking-env test + keep-list)

The swarm reviewed PR #5 (8 reviewers; the telemetry fix from #4 is now
live, so only 13 findings vs 43 on the comparably-clean #4 — the fix
works). Folded in the two warranted ones:

- engine: keep MAX_THINKING_TOKENS in claudeEnv() so a globally-set value
  reaches the CLI too (not just the per-spec :max append). (minimax)
- test: TestRunPassInjectsThinkingTokens verifies runPass actually puts
  MAX_THINKING_TOKENS in the subprocess env (31999 for :max, unset for a
  plain spec) — the parse was tested, the injection wasn't. (minimax)

The MAX_THINKING_TOKENS-is-unverified concern (minimax, qwen) is the same
caveat already documented; left as-is. gofmt/vet/test -race green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/gadfly/engine.go

@@ -221,7 +221,7 @@ func (e *claudeCodeEngine) runPass(ctx context.Context, system, task string, _ i
 func claudeEnv() []string {
 	keep := func(k string) bool {
 		switch k {
-		case "PATH", "HOME", "USER", "LOGNAME", "TMPDIR", "LANG", "TERM", "SHELL":
+		case "PATH", "HOME", "USER", "LOGNAME", "TMPDIR", "LANG", "TERM", "SHELL", "MAX_THINKING_TOKENS":
 			return true
 		}
 		return strings.HasPrefix(k, "LC_") ||

cmd/gadfly/engine_test.go

@@ -252,3 +252,30 @@ func TestClaudeCodeThinkingEnvOverrideKeepsSuffix(t *testing.T) {
 		t.Errorf("thinkingTokens = %d, want %d (suffix still applies)", e.thinkingTokens, maxThinkingTokens)
 	}
 }
+
+// TestRunPassInjectsThinkingTokens verifies the engine actually puts
+// MAX_THINKING_TOKENS into the subprocess env for a ":max" spec (and not for a
+// plain spec). The stub echoes the value it received back as the result.
+func TestRunPassInjectsThinkingTokens(t *testing.T) {
+	t.Setenv("GADFLY_CLAUDE_MODEL", "")
+	t.Setenv("MAX_THINKING_TOKENS", "") // not in the test's own env
+	dir := t.TempDir()
+	stub := dir + "/claude-stub.sh"
+	// Report the env var the CLI was launched with.
+	script := "#!/bin/sh\nprintf '{\"result\":\"MTT=%s\",\"is_error\":false}' \"${MAX_THINKING_TOKENS:-unset}\"\n"
+	if err := os.WriteFile(stub, []byte(script), 0o755); err != nil {
+		t.Fatal(err)
+	}
+
+	maxEng := newClaudeCodeEngine("claude-code/opus:max", dir)
+	maxEng.bin = stub
+	if out, err := maxEng.runPass(context.Background(), "s", "t", 0); err != nil || out != "MTT=31999" {
+		t.Fatalf(":max run: got (%q, %v), want (MTT=31999, nil)", out, err)
+	}
+
+	plainEng := newClaudeCodeEngine("claude-code/opus", dir)
+	plainEng.bin = stub
+	if out, err := plainEng.runPass(context.Background(), "s", "t", 0); err != nil || out != "MTT=unset" {
+		t.Fatalf("plain run: got (%q, %v), want (MTT=unset, nil)", out, err)
+	}
+}